Chapter 24 MySQL Performance Schema

Table of Contents

24.1 Performance Schema Quick Start
24.2 Performance Schema Build and Startup Configuration
24.2.1 Performance Schema Build Configuration
24.2.2 Performance Schema Startup Configuration
24.3 Performance Schema Runtime Configuration
24.3.1 Performance Schema Event Timing
24.3.2 Performance Schema Event Filtering
24.3.3 Event Pre-Filtering
24.3.4 Pre-Filtering by Instrument
24.3.5 Pre-Filtering by Object
24.3.6 Pre-Filtering by Thread
24.3.7 Pre-Filtering by Consumer
24.3.8 Example Consumer Configurations
24.3.9 Naming Instruments or Consumers for Filtering Operations
24.3.10 Determining What Is Instrumented
24.4 Performance Schema Queries
24.5 Performance Schema Instrument Naming Conventions
24.6 Performance Schema Status Monitoring
24.7 Performance Schema Atom and Molecule Events
24.8 Performance Schema Statement Digests
24.9 Performance Schema General Table Characteristics
24.10 Performance Schema Table Descriptions
24.10.1 Performance Schema Table Index
24.10.2 Performance Schema Setup Tables
24.10.3 Performance Schema Instance Tables
24.10.4 Performance Schema Wait Event Tables
24.10.5 Performance Schema Stage Event Tables
24.10.6 Performance Schema Statement Event Tables
24.10.7 Performance Schema Transaction Tables
24.10.8 Performance Schema Connection Tables
24.10.9 Performance Schema Connection Attribute Tables
24.10.10 Performance Schema User Variable Tables
24.10.11 Performance Schema Replication Tables
24.10.12 Performance Schema Lock Tables
24.10.13 Performance Schema System Variable Tables
24.10.14 Performance Schema Status Variable Tables
24.10.15 Performance Schema Summary Tables
24.10.16 Performance Schema Miscellaneous Tables
24.11 Performance Schema Option and Variable Reference
24.12 Performance Schema Command Options
24.13 Performance Schema System Variables
24.14 Performance Schema Status Variables
24.15 The Performance Schema Memory-Allocation Model
24.16 Performance Schema and Plugins
24.17 Using the Performance Schema to Diagnose Problems
24.17.1 Query Profiling Using Performance Schema
24.18 Migrating to Performance Schema System and Status Variable Tables

The MySQL Performance Schema is a feature for monitoring MySQL Server execution at a low level. The Performance Schema has these characteristics:

  • The Performance Schema provides a way to inspect internal execution of the server at runtime. It is implemented using the PERFORMANCE_SCHEMA storage engine and the performance_schema database. The Performance Schema focuses primarily on performance data. This differs from INFORMATION_SCHEMA, which serves for inspection of metadata.

  • The Performance Schema monitors server events. An event is anything the server does that takes time and has been instrumented so that timing information can be collected. In general, an event could be a function call, a wait for the operating system, a stage of an SQL statement execution such as parsing or sorting, or an entire statement or group of statements. Event collection provides access to information about synchronization calls (such as for mutexes) file and table I/O, table locks, and so forth for the server and for several storage engines.

  • Performance Schema events are distinct from events written to the server's binary log (which describe data modifications) and Event Scheduler events (which are a type of stored program).

  • Performance Schema events are specific to a given instance of the MySQL Server. Performance Schema tables are considered local to the server, and changes to them are not replicated or written to the binary log.

  • Current events are available, as well as event histories and summaries. This enables you to determine how many times instrumented activities were performed and how much time they took. Event information is available to show the activities of specific threads, or activity associated with particular objects such as a mutex or file.

  • The PERFORMANCE_SCHEMA storage engine collects event data using instrumentation points in server source code.

  • Collected events are stored in tables in the performance_schema database. These tables can be queried using SELECT statements like other tables.

  • Performance Schema configuration can be modified dynamically by updating tables in the performance_schema database through SQL statements. Configuration changes affect data collection immediately.

  • Tables in the Performance Schema are in-memory tables that use no persistent on-disk storage. The contents are repopulated beginning at server startup and discarded at server shutdown.

  • Monitoring is available on all platforms supported by MySQL.

    Some limitations might apply: The types of timers might vary per platform. Instruments that apply to storage engines might not be implemented for all storage engines. Instrumentation of each third-party engine is the responsibility of the engine maintainer. See also Section C.8, “Restrictions on Performance Schema”.

  • Data collection is implemented by modifying the server source code to add instrumentation. There are no separate threads associated with the Performance Schema, unlike other features such as replication or the Event Scheduler.

The Performance Schema is intended to provide access to useful information about server execution while having minimal impact on server performance. The implementation follows these design goals:

  • Activating the Performance Schema causes no changes in server behavior. For example, it does not cause thread scheduling to change, and it does not cause query execution plans (as shown by EXPLAIN) to change.

  • Server monitoring occurs continuously and unobtrusively with very little overhead. Activating the Performance Schema does not make the server unusable.

  • The parser is unchanged. There are no new keywords or statements.

  • Execution of server code proceeds normally even if the Performance Schema fails internally.

  • When there is a choice between performing processing during event collection initially or during event retrieval later, priority is given to making collection faster. This is because collection is ongoing whereas retrieval is on demand and might never happen at all.

  • It is easy to add new instrumentation points.

  • Instrumentation is versioned. If the instrumentation implementation changes, previously instrumented code will continue to work. This benefits developers of third-party plugins because it is not necessary to upgrade each plugin to stay synchronized with the latest Performance Schema changes.

Note

The MySQL sys schema is a set of objects that provides convenient access to data collected by the Performance Schema. The sys schema is installed by default as of MySQL 5.7.7. For usage instructions, see Chapter 25, MySQL sys Schema.

24.1 Performance Schema Quick Start

This section briefly introduces the Performance Schema with examples that show how to use it. For additional examples, see Section 24.17, “Using the Performance Schema to Diagnose Problems”.

For the Performance Schema to be available, support for it must have been configured when MySQL was built. You can verify whether this is the case by checking the server's help output. If the Performance Schema is available, the output will mention several variables with names that begin with performance_schema:

shell> mysqld --verbose --help
...
  --performance_schema
                      Enable the performance schema.
  --performance_schema_events_waits_history_long_size=#
                      Number of rows in events_waits_history_long.
...

If such variables do not appear in the output, your server has not been built to support the Performance Schema. In this case, see Section 24.2, “Performance Schema Build and Startup Configuration”.

Assuming that the Performance Schema is available, it is enabled by default. To enable or disable it explicitly, start the server with the performance_schema variable set to an appropriate value. For example, use these lines in your my.cnf file:

[mysqld]
performance_schema=ON

When the server starts, it sees performance_schema and attempts to initialize the Performance Schema. To verify successful initialization, use this statement:

mysql> SHOW VARIABLES LIKE 'performance_schema';
+--------------------+-------+
| Variable_name      | Value |
+--------------------+-------+
| performance_schema | ON    |
+--------------------+-------+

A value of ON means that the Performance Schema initialized successfully and is ready for use. A value of OFF means that some error occurred. Check the server error log for information about what went wrong.

The Performance Schema is implemented as a storage engine. If this engine is available (which you should already have checked earlier), you should see it listed with a SUPPORT value of YES in the output from the INFORMATION_SCHEMA.ENGINES table or the SHOW ENGINES statement:

mysql> SELECT * FROM INFORMATION_SCHEMA.ENGINES
       WHERE ENGINE='PERFORMANCE_SCHEMA'\G
*************************** 1. row ***************************
      ENGINE: PERFORMANCE_SCHEMA
     SUPPORT: YES
     COMMENT: Performance Schema
TRANSACTIONS: NO
          XA: NO
  SAVEPOINTS: NO

mysql> SHOW ENGINES\G
...
      Engine: PERFORMANCE_SCHEMA
     Support: YES
     Comment: Performance Schema
Transactions: NO
          XA: NO
  Savepoints: NO
...

The PERFORMANCE_SCHEMA storage engine operates on tables in the performance_schema database. You can make performance_schema the default database so that references to its tables need not be qualified with the database name:

mysql> USE performance_schema;

Many examples in this chapter assume performance_schema as the default database.

Performance Schema tables are stored in the performance_schema database. Information about the structure of this database and its tables can be obtained, as for any other database, by selecting from the INFORMATION_SCHEMA database or by using SHOW statements. For example, use either of these statements to see what Performance Schema tables exist:

mysql> SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES
       WHERE TABLE_SCHEMA = 'performance_schema';
+------------------------------------------------------+
| TABLE_NAME                                           |
+------------------------------------------------------+
| accounts                                             |
| cond_instances                                       |
...
| events_stages_current                                |
| events_stages_history                                |
| events_stages_history_long                           |
| events_stages_summary_by_account_by_event_name       |
| events_stages_summary_by_host_by_event_name          |
| events_stages_summary_by_thread_by_event_name        |
| events_stages_summary_by_user_by_event_name          |
| events_stages_summary_global_by_event_name           |
| events_statements_current                            |
| events_statements_history                            |
| events_statements_history_long                       |
...
| file_instances                                       |
| file_summary_by_event_name                           |
| file_summary_by_instance                             |
| host_cache                                           |
| hosts                                                |
| memory_summary_by_account_by_event_name              |
| memory_summary_by_host_by_event_name                 |
| memory_summary_by_thread_by_event_name               |
| memory_summary_by_user_by_event_name                 |
| memory_summary_global_by_event_name                  |
| metadata_locks                                       |
| mutex_instances                                      |
| objects_summary_global_by_type                       |
| performance_timers                                   |
| replication_connection_configuration                 |
| replication_connection_status                        |
| replication_applier_configuration                    |
| replication_applier_status                           |
| replication_applier_status_by_coordinator            |
| replication_applier_status_by_worker                 |
| rwlock_instances                                     |
| session_account_connect_attrs                        |
| session_connect_attrs                                |
| setup_actors                                         |
| setup_consumers                                      |
| setup_instruments                                    |
| setup_objects                                        |
| setup_timers                                         |
| socket_instances                                     |
| socket_summary_by_event_name                         |
| socket_summary_by_instance                           |
| table_handles                                        |
| table_io_waits_summary_by_index_usage                |
| table_io_waits_summary_by_table                      |
| table_lock_waits_summary_by_table                    |
| threads                                              |
| users                                                |
+------------------------------------------------------+

mysql> SHOW TABLES FROM performance_schema;
+------------------------------------------------------+
| Tables_in_performance_schema                         |
+------------------------------------------------------+
| accounts                                             |
| cond_instances                                       |
| events_stages_current                                |
| events_stages_history                                |
| events_stages_history_long                           |
...

The number of Performance Schema tables increases over time as implementation of additional instrumentation proceeds.

The name of the performance_schema database is lowercase, as are the names of tables within it. Queries should specify the names in lowercase.

To see the structure of individual tables, use SHOW CREATE TABLE:

mysql> SHOW CREATE TABLE setup_timers\G
*************************** 1. row ***************************
       Table: setup_timers
Create Table: CREATE TABLE `setup_timers` (
  `NAME` varchar(64) NOT NULL,
  `TIMER_NAME` enum('CYCLE','NANOSECOND','MICROSECOND','MILLISECOND','TICK')
   NOT NULL
) ENGINE=PERFORMANCE_SCHEMA DEFAULT CHARSET=utf8

Table structure is also available by selecting from tables such as INFORMATION_SCHEMA.COLUMNS or by using statements such as SHOW COLUMNS.

Tables in the performance_schema database can be grouped according to the type of information in them: Current events, event histories and summaries, object instances, and setup (configuration) information. The following examples illustrate a few uses for these tables. For detailed information about the tables in each group, see Section 24.10, “Performance Schema Table Descriptions”.

Initially, not all instruments and consumers are enabled, so the performance schema does not collect all events. To turn all of these on and enable event timing, execute two statements (the row counts may differ depending on MySQL version):

mysql> UPDATE setup_instruments SET ENABLED = 'YES', TIMED = 'YES';
Query OK, 560 rows affected (0.04 sec)
mysql> UPDATE setup_consumers SET ENABLED = 'YES';
Query OK, 10 rows affected (0.00 sec)

To see what the server is doing at the moment, examine the events_waits_current table. It contains one row per thread showing each thread's most recent monitored event:

mysql> SELECT * FROM events_waits_current\G
*************************** 1. row ***************************
            THREAD_ID: 0
             EVENT_ID: 5523
         END_EVENT_ID: 5523
           EVENT_NAME: wait/synch/mutex/mysys/THR_LOCK::mutex
               SOURCE: thr_lock.c:525
          TIMER_START: 201660494489586
            TIMER_END: 201660494576112
           TIMER_WAIT: 86526
                SPINS: NULL
        OBJECT_SCHEMA: NULL
          OBJECT_NAME: NULL
           INDEX_NAME: NULL
          OBJECT_TYPE: NULL
OBJECT_INSTANCE_BEGIN: 142270668
     NESTING_EVENT_ID: NULL
   NESTING_EVENT_TYPE: NULL
            OPERATION: lock
      NUMBER_OF_BYTES: NULL
                FLAGS: 0
...

This event indicates that thread 0 was waiting for 86,526 picoseconds to acquire a lock on THR_LOCK::mutex, a mutex in the mysys subsystem. The first few columns provide the following information:

  • The ID columns indicate which thread the event comes from and the event number.

  • EVENT_NAME indicates what was instrumented and SOURCE indicates which source file contains the instrumented code.

  • The timer columns show when the event started and stopped and how long it took. If an event is still in progress, the TIMER_END and TIMER_WAIT values are NULL. Timer values are approximate and expressed in picoseconds. For information about timers and event time collection, see Section 24.3.1, “Performance Schema Event Timing”.

The history tables contain the same kind of rows as the current-events table but have more rows and show what the server has been doing recently rather than currently. The events_waits_history and events_waits_history_long tables contain the most recent 10 events per thread and most recent 10,000 events, respectively. For example, to see information for recent events produced by thread 13, do this:

mysql> SELECT EVENT_ID, EVENT_NAME, TIMER_WAIT
       FROM events_waits_history WHERE THREAD_ID = 13
       ORDER BY EVENT_ID;
+----------+-----------------------------------------+------------+
| EVENT_ID | EVENT_NAME                              | TIMER_WAIT |
+----------+-----------------------------------------+------------+
|       86 | wait/synch/mutex/mysys/THR_LOCK::mutex  |     686322 |
|       87 | wait/synch/mutex/mysys/THR_LOCK_malloc  |     320535 |
|       88 | wait/synch/mutex/mysys/THR_LOCK_malloc  |     339390 |
|       89 | wait/synch/mutex/mysys/THR_LOCK_malloc  |     377100 |
|       90 | wait/synch/mutex/sql/LOCK_plugin        |     614673 |
|       91 | wait/synch/mutex/sql/LOCK_open          |     659925 |
|       92 | wait/synch/mutex/sql/THD::LOCK_thd_data |     494001 |
|       93 | wait/synch/mutex/mysys/THR_LOCK_malloc  |     222489 |
|       94 | wait/synch/mutex/mysys/THR_LOCK_malloc  |     214947 |
|       95 | wait/synch/mutex/mysys/LOCK_alarm       |     312993 |
+----------+-----------------------------------------+------------+

As new events are added to a history table, older events are discarded if the table is full.

Summary tables provide aggregated information for all events over time. The tables in this group summarize event data in different ways. To see which instruments have been executed the most times or have taken the most wait time, sort the events_waits_summary_global_by_event_name table on the COUNT_STAR or SUM_TIMER_WAIT column, which correspond to a COUNT(*) or SUM(TIMER_WAIT) value, respectively, calculated over all events:

mysql> SELECT EVENT_NAME, COUNT_STAR
       FROM events_waits_summary_global_by_event_name
       ORDER BY COUNT_STAR DESC LIMIT 10;
+---------------------------------------------------+------------+
| EVENT_NAME                                        | COUNT_STAR |
+---------------------------------------------------+------------+
| wait/synch/mutex/mysys/THR_LOCK_malloc            |       6419 |
| wait/io/file/sql/FRM                              |        452 |
| wait/synch/mutex/sql/LOCK_plugin                  |        337 |
| wait/synch/mutex/mysys/THR_LOCK_open              |        187 |
| wait/synch/mutex/mysys/LOCK_alarm                 |        147 |
| wait/synch/mutex/sql/THD::LOCK_thd_data           |        115 |
| wait/io/file/myisam/kfile                         |        102 |
| wait/synch/mutex/sql/LOCK_global_system_variables |         89 |
| wait/synch/mutex/mysys/THR_LOCK::mutex            |         89 |
| wait/synch/mutex/sql/LOCK_open                    |         88 |
+---------------------------------------------------+------------+

mysql> SELECT EVENT_NAME, SUM_TIMER_WAIT
       FROM events_waits_summary_global_by_event_name
       ORDER BY SUM_TIMER_WAIT DESC LIMIT 10;
+----------------------------------------+----------------+
| EVENT_NAME                             | SUM_TIMER_WAIT |
+----------------------------------------+----------------+
| wait/io/file/sql/MYSQL_LOG             |     1599816582 |
| wait/synch/mutex/mysys/THR_LOCK_malloc |     1530083250 |
| wait/io/file/sql/binlog_index          |     1385291934 |
| wait/io/file/sql/FRM                   |     1292823243 |
| wait/io/file/myisam/kfile              |      411193611 |
| wait/io/file/myisam/dfile              |      322401645 |
| wait/synch/mutex/mysys/LOCK_alarm      |      145126935 |
| wait/io/file/sql/casetest              |      104324715 |
| wait/synch/mutex/sql/LOCK_plugin       |       86027823 |
| wait/io/file/sql/pid                   |       72591750 |
+----------------------------------------+----------------+

These results show that the THR_LOCK_malloc mutex is hot, both in terms of how often it is used and amount of time that threads wait attempting to acquire it.

Note

The THR_LOCK_malloc mutex is used only in debug builds. In production builds it is not hot because it is nonexistent.

Instance tables document what types of objects are instrumented. An instrumented object, when used by the server, produces an event. These tables provide event names and explanatory notes or status information. For example, the file_instances table lists instances of instruments for file I/O operations and their associated files:

mysql> SELECT * FROM file_instances\G
*************************** 1. row ***************************
 FILE_NAME: /opt/mysql-log/60500/binlog.000007
EVENT_NAME: wait/io/file/sql/binlog
OPEN_COUNT: 0
*************************** 2. row ***************************
 FILE_NAME: /opt/mysql/60500/data/mysql/tables_priv.MYI
EVENT_NAME: wait/io/file/myisam/kfile
OPEN_COUNT: 1
*************************** 3. row ***************************
 FILE_NAME: /opt/mysql/60500/data/mysql/columns_priv.MYI
EVENT_NAME: wait/io/file/myisam/kfile
OPEN_COUNT: 1
...

Setup tables are used to configure and display monitoring characteristics. For example, to see which event timers are selected, query the setup_timers tables:

mysql> SELECT * FROM setup_timers;
+-------------+-------------+
| NAME        | TIMER_NAME  |
+-------------+-------------+
| idle        | MICROSECOND |
| wait        | CYCLE       |
| stage       | NANOSECOND  |
| statement   | NANOSECOND  |
| transaction | NANOSECOND  |
+-------------+-------------+

setup_instruments lists the set of instruments for which events can be collected and shows which of them are enabled:

mysql> SELECT * FROM setup_instruments;
+------------------------------------------------------------+---------+-------+
| NAME                                                       | ENABLED | TIMED |
+------------------------------------------------------------+---------+-------+
...
| wait/synch/mutex/sql/LOCK_global_read_lock                 | YES     | YES   |
| wait/synch/mutex/sql/LOCK_global_system_variables          | YES     | YES   |
| wait/synch/mutex/sql/LOCK_lock_db                          | YES     | YES   |
| wait/synch/mutex/sql/LOCK_manager                          | YES     | YES   |
...
| wait/synch/rwlock/sql/LOCK_grant                           | YES     | YES   |
| wait/synch/rwlock/sql/LOGGER::LOCK_logger                  | YES     | YES   |
| wait/synch/rwlock/sql/LOCK_sys_init_connect                | YES     | YES   |
| wait/synch/rwlock/sql/LOCK_sys_init_slave                  | YES     | YES   |
...
| wait/io/file/sql/binlog                                    | YES     | YES   |
| wait/io/file/sql/binlog_index                              | YES     | YES   |
| wait/io/file/sql/casetest                                  | YES     | YES   |
| wait/io/file/sql/dbopt                                     | YES     | YES   |
...

To understand how to interpret instrument names, see Section 24.5, “Performance Schema Instrument Naming Conventions”.

To control whether events are collected for an instrument, set its ENABLED value to YES or NO. For example:

mysql> UPDATE setup_instruments SET ENABLED = 'NO'
       WHERE NAME = 'wait/synch/mutex/sql/LOCK_mysql_create_db';

The Performance Schema uses collected events to update tables in the performance_schema database, which act as consumers of event information. The setup_consumers table lists the available consumers and which are enabled:

mysql> SELECT * FROM setup_consumers;
+----------------------------------+---------+
| NAME                             | ENABLED |
+----------------------------------+---------+
| events_stages_current            | NO      |
| events_stages_history            | NO      |
| events_stages_history_long       | NO      |
| events_statements_current        | YES     |
| events_statements_history        | YES     |
| events_statements_history_long   | NO      |
| events_transactions_current      | NO      |
| events_transactions_history      | NO      |
| events_transactions_history_long | NO      |
| events_waits_current             | NO      |
| events_waits_history             | NO      |
| events_waits_history_long        | NO      |
| global_instrumentation           | YES     |
| thread_instrumentation           | YES     |
| statements_digest                | YES     |
+----------------------------------+---------+

To control whether the Performance Schema maintains a consumer as a destination for event information, set its ENABLED value.

For more information about the setup tables and how to use them to control event collection, see Section 24.3.2, “Performance Schema Event Filtering”.

There are some miscellaneous tables that do not fall into any of the previous groups. For example, performance_timers lists the available event timers and their characteristics. For information about timers, see Section 24.3.1, “Performance Schema Event Timing”.

24.2 Performance Schema Build and Startup Configuration

To use the MySQL Performance Schema, these configuration considerations apply:

24.2.1 Performance Schema Build Configuration

For the Performance Schema to be available, it must be configured into the MySQL server at build time. Binary MySQL distributions provided by Oracle Corporation are configured to support the Performance Schema. If you use a binary MySQL distribution from another provider, check with the provider whether the distribution has been appropriately configured.

As of MySQL 5.7.9, the Performance Schema is mandatory and always compiled in. Before 5.7.9, if you build MySQL from a source distribution, enable the Performance Schema by running CMake with the WITH_PERFSCHEMA_STORAGE_ENGINE option enabled:

shell> cmake . -DWITH_PERFSCHEMA_STORAGE_ENGINE=1

Configuring MySQL with the -DWITHOUT_PERFSCHEMA_STORAGE_ENGINE=1 option prevents inclusion of the Performance Schema, so if you want it included, do not use this option.

As of MySQL 5.7.3, it is possible to enable the Performance Schema but exclude certain parts of the instrumentation. For example, to enable the Performance Schema but exclude stage and statement instrumentation, do this:

shell> cmake . -DWITH_PERFSCHEMA_STORAGE_ENGINE=1 \
        -DDISABLE_PSI_STAGE=1 \
        -DDISABLE_PSI_STATEMENT=1

For more information, see the descriptions of the DISABLE_PSI_XXX CMake options in Section 2.9.4, “MySQL Source-Configuration Options”.

If you install MySQL over a previous installation that was configured without the Performance Schema (or with an older version of the Performance Schema that may not have all the current tables), run mysql_upgrade after starting the server to ensure that the performance_schema database exists with all current tables. Then restart the server. One indication that you need to do this is the presence of messages such as the following in the error log:

[ERROR] Native table 'performance_schema'.'events_waits_history'
has the wrong structure
[ERROR] Native table 'performance_schema'.'events_waits_history_long'
has the wrong structure
...

To verify whether a server was built with Performance Schema support, check its help output. If the Performance Schema is available, the output will mention several variables with names that begin with performance_schema:

shell> mysqld --verbose --help
...
  --performance_schema
                      Enable the performance schema.
  --performance_schema_events_waits_history_long_size=#
                      Number of rows in events_waits_history_long.
...

You can also connect to the server and look for a line that names the PERFORMANCE_SCHEMA storage engine in the output from SHOW ENGINES:

mysql> SHOW ENGINES\G
...
      Engine: PERFORMANCE_SCHEMA
     Support: YES
     Comment: Performance Schema
Transactions: NO
          XA: NO
  Savepoints: NO
...

If the Performance Schema was not configured into the server at build time, no row for PERFORMANCE_SCHEMA will appear in the output from SHOW ENGINES. You might see performance_schema listed in the output from SHOW DATABASES, but it will have no tables and you will not be able to use it.

A line for PERFORMANCE_SCHEMA in the SHOW ENGINES output means that the Performance Schema is available, not that it is enabled. To enable it, you must do so at server startup, as described in the next section.

24.2.2 Performance Schema Startup Configuration

Assuming that the Performance Schema is available, it is enabled by default. To enable or disable it explicitly, start the server with the performance_schema variable set to an appropriate value. For example, use these lines in your my.cnf file:

[mysqld]
performance_schema=ON

If the server is unable to allocate any internal buffer during Performance Schema initialization, the Performance Schema disables itself and sets performance_schema to OFF, and the server runs without instrumentation.

The Performance Schema also permits instrument and consumer configuration at server startup.

To control an instrument at server startup, use an option of this form:

--performance-schema-instrument='instrument_name=value'

Here, instrument_name is an instrument name such as wait/synch/mutex/sql/LOCK_open, and value is one of these values:

  • OFF, FALSE, or 0: Disable the instrument

  • ON, TRUE, or 1: Enable and time the instrument

  • COUNTED: Enable and count (rather than time) the instrument

Each --performance-schema-instrument option can specify only one instrument name, but multiple instances of the option can be given to configure multiple instruments. In addition, patterns are permitted in instrument names to configure instruments that match the pattern. To configure all condition synchronization instruments as enabled and counted, use this option:

--performance-schema-instrument='wait/synch/cond/%=COUNTED'

To disable all instruments, use this option:

--performance-schema-instrument='%=OFF'

Exception: The memory/performance_schema/% instruments are built in and cannot be disabled at startup.

Longer instrument name strings take precedence over shorter pattern names, regardless of order. For information about specifying patterns to select instruments, see Section 24.3.9, “Naming Instruments or Consumers for Filtering Operations”.

An unrecognized instrument name is ignored. It is possible that a plugin installed later may create the instrument, at which time the name is recognized and configured.

To control a consumer at server startup, use an option of this form:

--performance-schema-consumer-consumer_name=value

Here, consumer_name is a consumer name such as events_waits_history, and value is one of these values:

  • OFF, FALSE, or 0: Do not collect events for the consumer

  • ON, TRUE, or 1: Collect events for the consumer

For example, to enable the events_waits_history consumer, use this option:

--performance-schema-consumer-events-waits-history=ON

The permitted consumer names can be found by examining the setup_consumers table. Patterns are not permitted. Consumer names in the setup_consumers table use underscores, but for consumers set at startup, dashes and underscores within the name are equivalent.

The Performance Schema includes several system variables that provide configuration information:

mysql> SHOW VARIABLES LIKE 'perf%';
+--------------------------------------------------------+---------+
| Variable_name                                          | Value   |
+--------------------------------------------------------+---------+
| performance_schema                                     | ON      |
| performance_schema_accounts_size                       | 100     |
| performance_schema_digests_size                        | 200     |
| performance_schema_events_stages_history_long_size     | 10000   |
| performance_schema_events_stages_history_size          | 10      |
| performance_schema_events_statements_history_long_size | 10000   |
| performance_schema_events_statements_history_size      | 10      |
| performance_schema_events_waits_history_long_size      | 10000   |
| performance_schema_events_waits_history_size           | 10      |
| performance_schema_hosts_size                          | 100     |
| performance_schema_max_cond_classes                    | 80      |
| performance_schema_max_cond_instances                  | 1000    |
...

The performance_schema variable is ON or OFF to indicate whether the Performance Schema is enabled or disabled. The other variables indicate table sizes (number of rows) or memory allocation values.

Note

With the Performance Schema enabled, the number of Performance Schema instances affects the server memory footprint, perhaps to a large extent. Before MySQL 5.7.6, it may be necessary to tune the values of Performance Schema system variables to find the number of instances that balances insufficient instrumentation against excessive memory consumption. As of MySQL 5.7.6, the Performance Schema autoscales many parameters to use memory only as required; see Section 24.15, “The Performance Schema Memory-Allocation Model”.

To change the value of Performance Schema system variables, set them at server startup. For example, put the following lines in a my.cnf file to change the sizes of the history tables for wait events:

[mysqld]
performance_schema
performance_schema_events_waits_history_size=20
performance_schema_events_waits_history_long_size=15000

The Performance Schema automatically sizes the values of several of its parameters at server startup if they are not set explicitly. For example, it sizes the parameters that control the sizes of the events waits tables this way. As of MySQL 5.7.6, the Performance Schema allocates memory incrementally, scaling its memory use to actual server load, instead of allocating all the memory it needs during server startup. Consequently, many sizing parameters need not be set at all. To see which parameters are autosized or autoscaled, use mysqld --verbose --help and examine the option descriptions, or see Section 24.13, “Performance Schema System Variables”.

For each autosized parameter that is not set at server startup (or is set to −1), the Performance Schema determines how to set its value based on the value of the following system values, which are considered as hints about how you have configured your MySQL server:

max_connections
open_files_limit
table_definition_cache
table_open_cache

To override autosizing or autoscaling for a given parameter, set it to a value other than −1 at startup. In this case, the Performance Schema assigns it the specified value.

At runtime, SHOW VARIABLES displays the actual values that autosized parameters were set to. Autoscaled parameters display with a value of −1.

If the Performance Schema is disabled, its autosized and autoscaled parameters remain set to −1 and SHOW VARIABLES displays −1.

24.3 Performance Schema Runtime Configuration

Performance Schema setup tables contain information about monitoring configuration:

mysql> SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES
       WHERE TABLE_SCHEMA = 'performance_schema'
       AND TABLE_NAME LIKE 'setup%';
+-------------------+
| TABLE_NAME        |
+-------------------+
| setup_actors      |
| setup_consumers   |
| setup_instruments |
| setup_objects     |
| setup_timers      |
+-------------------+

You can examine the contents of these tables to obtain information about Performance Schema monitoring characteristics. If you have the UPDATE privilege, you can change Performance Schema operation by modifying setup tables to affect how monitoring occurs. For additional details about these tables, see Section 24.10.2, “Performance Schema Setup Tables”.

To see which event timers are selected, query the setup_timers tables:

mysql> SELECT * FROM setup_timers;
+-------------+-------------+
| NAME        | TIMER_NAME  |
+-------------+-------------+
| idle        | MICROSECOND |
| wait        | CYCLE       |
| stage       | NANOSECOND  |
| statement   | NANOSECOND  |
| transaction | NANOSECOND  |
+-------------+-------------+

The NAME value indicates the type of instrument to which the timer applies, and TIMER_NAME indicates which timer applies to those instruments. The timer applies to instruments where their name begins with a component matching the NAME value.

To change the timer, update the NAME value. For example, to use the NANOSECOND timer for the wait timer:

mysql> UPDATE setup_timers SET TIMER_NAME = 'NANOSECOND'
       WHERE NAME = 'wait';
mysql> SELECT * FROM setup_timers;
+-------------+-------------+
| NAME        | TIMER_NAME  |
+-------------+-------------+
| idle        | MICROSECOND |
| wait        | NANOSECOND  |
| stage       | NANOSECOND  |
| statement   | NANOSECOND  |
| transaction | NANOSECOND  |
+-------------+-------------+

For discussion of timers, see Section 24.3.1, “Performance Schema Event Timing”.

The setup_instruments and setup_consumers tables list the instruments for which events can be collected and the types of consumers for which event information actually is collected, respectively. Other setup tables enable further modification of the monitoring configuration. Section 24.3.2, “Performance Schema Event Filtering”, discusses how you can modify these tables to affect event collection.

If there are Performance Schema configuration changes that must be made at runtime using SQL statements and you would like these changes to take effect each time the server starts, put the statements in a file and start the server with the --init-file=file_name option. This strategy can also be useful if you have multiple monitoring configurations, each tailored to produce a different kind of monitoring, such as casual server health monitoring, incident investigation, application behavior troubleshooting, and so forth. Put the statements for each monitoring configuration into their own file and specify the appropriate file as the --init-file argument when you start the server.

24.3.1 Performance Schema Event Timing

Events are collected by means of instrumentation added to the server source code. Instruments time events, which is how the Performance Schema provides an idea of how long events take. It is also possible to configure instruments not to collect timing information. This section discusses the available timers and their characteristics, and how timing values are represented in events.

Performance Schema Timers

Two Performance Schema tables provide timer information:

Each timer row in setup_timers must refer to one of the timers listed in performance_timers.

Timers vary in precision and amount of overhead. To see what timers are available and their characteristics, check the performance_timers table:

mysql> SELECT * FROM performance_timers;
+-------------+-----------------+------------------+----------------+
| TIMER_NAME  | TIMER_FREQUENCY | TIMER_RESOLUTION | TIMER_OVERHEAD |
+-------------+-----------------+------------------+----------------+
| CYCLE       |      2389029850 |                1 |             72 |
| NANOSECOND  |      1000000000 |                1 |            112 |
| MICROSECOND |         1000000 |                1 |            136 |
| MILLISECOND |            1036 |                1 |            168 |
| TICK        |             105 |                1 |           2416 |
+-------------+-----------------+------------------+----------------+

The columns have these meanings:

  • The TIMER_NAME column shows the names of the available timers. CYCLE refers to the timer that is based on the CPU (processor) cycle counter. The timers in setup_timers that you can use are those that do not have NULL in the other columns. If the values associated with a given timer name are NULL, that timer is not supported on your platform.

  • TIMER_FREQUENCY indicates the number of timer units per second. For a cycle timer, the frequency is generally related to the CPU speed. The value shown was obtained on a system with a 2.4GHz processor. The other timers are based on fixed fractions of seconds. For TICK, the frequency may vary by platform (for example, some use 100 ticks/second, others 1000 ticks/second).

  • TIMER_RESOLUTION indicates the number of timer units by which timer values increase at a time. If a timer has a resolution of 10, its value increases by 10 each time.

  • TIMER_OVERHEAD is the minimal number of cycles of overhead to obtain one timing with the given timer. The overhead per event is twice the value displayed because the timer is invoked at the beginning and end of the event.

To see which timers are in effect or to change timers, access the setup_timers table:

mysql> SELECT * FROM setup_timers;
+-------------+-------------+
| NAME        | TIMER_NAME  |
+-------------+-------------+
| idle        | MICROSECOND |
| wait        | CYCLE       |
| stage       | NANOSECOND  |
| statement   | NANOSECOND  |
| transaction | NANOSECOND  |
+-------------+-------------+

mysql> UPDATE setup_timers SET TIMER_NAME = 'MICROSECOND'
       WHERE NAME = 'idle';
mysql> SELECT * FROM setup_timers;
+-------------+-------------+
| NAME        | TIMER_NAME  |
+-------------+-------------+
| idle        | MICROSECOND |
| wait        | CYCLE       |
| stage       | NANOSECOND  |
| statement   | NANOSECOND  |
| transaction | NANOSECOND  |
+-------------+-------------+

By default, the Performance Schema uses the best timer available for each instrument type, but you can select a different one.

To time wait events, the most important criterion is to reduce overhead, at the possible expense of the timer accuracy, so using the CYCLE timer is the best.

The time a statement (or stage) takes to execute is in general orders of magnitude larger than the time it takes to execute a single wait. To time statements, the most important criterion is to have an accurate measure, which is not affected by changes in processor frequency, so using a timer which is not based on cycles is the best. The default timer for statements is NANOSECOND. The extra overhead compared to the CYCLE timer is not significant, because the overhead caused by calling a timer twice (once when the statement starts, once when it ends) is orders of magnitude less compared to the CPU time used to execute the statement itself. Using the CYCLE timer has no benefit here, only drawbacks.

The precision offered by the cycle counter depends on processor speed. If the processor runs at 1 GHz (one billion cycles/second) or higher, the cycle counter delivers sub-nanosecond precision. Using the cycle counter is much cheaper than getting the actual time of day. For example, the standard gettimeofday() function can take hundreds of cycles, which is an unacceptable overhead for data gathering that may occur thousands or millions of times per second.

Cycle counters also have disadvantages:

  • End users expect to see timings in wall-clock units, such as fractions of a second. Converting from cycles to fractions of seconds can be expensive. For this reason, the conversion is a quick and fairly rough multiplication operation.

  • Processor cycle rate might change, such as when a laptop goes into power-saving mode or when a CPU slows down to reduce heat generation. If a processor's cycle rate fluctuates, conversion from cycles to real-time units is subject to error.

  • Cycle counters might be unreliable or unavailable depending on the processor or the operating system. For example, on Pentiums, the instruction is RDTSC (an assembly-language rather than a C instruction) and it is theoretically possible for the operating system to prevent user-mode programs from using it.

  • Some processor details related to out-of-order execution or multiprocessor synchronization might cause the counter to seem fast or slow by up to 1000 cycles.

MySQL works with cycle counters on x386 (Windows, OS X, Linux, Solaris, and other Unix flavors), PowerPC, and IA-64.

Performance Schema Timer Representation in Events

Rows in Performance Schema tables that store current events and historical events have three columns to represent timing information: TIMER_START and TIMER_END indicate when an event started and finished, and TIMER_WAIT indicates event duration.

The setup_instruments table has an ENABLED column to indicate the instruments for which to collect events. The table also has a TIMED column to indicate which instruments are timed. If an instrument is not enabled, it produces no events. If an enabled instrument is not timed, events produced by the instrument have NULL for the TIMER_START, TIMER_END, and TIMER_WAIT timer values. This in turn causes those values to be ignored when calculating the sum, minimum, maximum, and average time values in summary tables.

Internally, times within events are stored in units given by the timer in effect when event timing begins. For display when events are retrieved from Performance Schema tables, times are shown in picoseconds (trillionths of a second) to normalize them to a standard unit, regardless of which timer is selected.

Modifications to the setup_timers table affect monitoring immediately. Events already in progress may use the original timer for the begin time and the new timer for the end time. To avoid unpredictable results after you make timer changes, use TRUNCATE TABLE to reset Performance Schema statistics.

The timer baseline (time zero) occurs at Performance Schema initialization during server startup. TIMER_START and TIMER_END values in events represent picoseconds since the baseline. TIMER_WAIT values are durations in picoseconds.

Picosecond values in events are approximate. Their accuracy is subject to the usual forms of error associated with conversion from one unit to another. If the CYCLE timer is used and the processor rate varies, there might be drift. For these reasons, it is not reasonable to look at the TIMER_START value for an event as an accurate measure of time elapsed since server startup. On the other hand, it is reasonable to use TIMER_START or TIMER_WAIT values in ORDER BY clauses to order events by start time or duration.

The choice of picoseconds in events rather than a value such as microseconds has a performance basis. One implementation goal was to show results in a uniform time unit, regardless of the timer. In an ideal world this time unit would look like a wall-clock unit and be reasonably precise; in other words, microseconds. But to convert cycles or nanoseconds to microseconds, it would be necessary to perform a division for every instrumentation. Division is expensive on many platforms. Multiplication is not expensive, so that is what is used. Therefore, the time unit is an integer multiple of the highest possible TIMER_FREQUENCY value, using a multiplier large enough to ensure that there is no major precision loss. The result is that the time unit is picoseconds. This precision is spurious, but the decision enables overhead to be minimized.

Before MySQL 5.7.8, while a wait, stage, statement, or transaction event is executing, the respective current-event tables display the event with TIMER_START populated, but with TIMER_END and TIMER_WAIT set to NULL:

events_waits_current
events_stages_current
events_statements_current
events_transactions_current

As of MySQL 5.7.8, current-event timing provides more information. To make it possible to determine how how long a not-yet-completed event has been running, the timer columns are set as follows:

  • TIMER_START is populated (unchanged from previous behavior)

  • TIMER_END is populated with the current timer value

  • TIMER_WAIT is populated with the time elapsed so far (TIMER_ENDTIMER_START)

Events that have not yet completed have an END_EVENT_ID value of NULL. To assess time elapsed so far for an event, use the TIMER_WAIT column. Therefore, to identify events that have not yet completed and have taken longer than N picoseconds thus far, monitoring applications can use this expression in queries:

WHERE END_EVENT_ID IS NULL AND TIMER_WAIT > N

Event identification as just described assumes that the corresponding instruments have ENABLED and TIMED set to YES and that the relevent consumers are enabled.

24.3.2 Performance Schema Event Filtering

Events are processed in a producer/consumer fashion:

  • Instrumented code is the source for events and produces events to be collected. The setup_instruments table lists the instruments for which events can be collected, whether they are enabled, and (for enabled instruments) whether to collect timing information:

    mysql> SELECT * FROM setup_instruments;
    +------------------------------------------------------------+---------+-------+
    | NAME                                                       | ENABLED | TIMED |
    +------------------------------------------------------------+---------+-------+
    ...
    | wait/synch/mutex/sql/LOCK_global_read_lock                 | YES     | YES   |
    | wait/synch/mutex/sql/LOCK_global_system_variables          | YES     | YES   |
    | wait/synch/mutex/sql/LOCK_lock_db                          | YES     | YES   |
    | wait/synch/mutex/sql/LOCK_manager                          | YES     | YES   |
    ...
    

    The setup_instruments table provides the most basic form of control over event production. To further refine event production based on the type of object or thread being monitored, other tables may be used as described in Section 24.3.3, “Event Pre-Filtering”.

  • Performance Schema tables are the destinations for events and consume events. The setup_consumers table lists the types of consumers to which event information can be sent and whether they are enabled:

    mysql> SELECT * FROM setup_consumers;
    +----------------------------------+---------+
    | NAME                             | ENABLED |
    +----------------------------------+---------+
    | events_stages_current            | NO      |
    | events_stages_history            | NO      |
    | events_stages_history_long       | NO      |
    | events_statements_current        | YES     |
    | events_statements_history        | YES     |
    | events_statements_history_long   | NO      |
    | events_transactions_current      | NO      |
    | events_transactions_history      | NO      |
    | events_transactions_history_long | NO      |
    | events_waits_current             | NO      |
    | events_waits_history             | NO      |
    | events_waits_history_long        | NO      |
    | global_instrumentation           | YES     |
    | thread_instrumentation           | YES     |
    | statements_digest                | YES     |
    +----------------------------------+---------+
    

Filtering can be done at different stages of performance monitoring:

  • Pre-filtering. This is done by modifying Performance Schema configuration so that only certain types of events are collected from producers, and collected events update only certain consumers. To do this, enable or disable instruments or consumers. Pre-filtering is done by the Performance Schema and has a global effect that applies to all users.

    Reasons to use pre-filtering:

    • To reduce overhead. Performance Schema overhead should be minimal even with all instruments enabled, but perhaps you want to reduce it further. Or you do not care about timing events and want to disable the timing code to eliminate timing overhead.

    • To avoid filling the current-events or history tables with events in which you have no interest. Pre-filtering leaves more room in these tables for instances of rows for enabled instrument types. If you enable only file instruments with pre-filtering, no rows are collected for nonfile instruments. With post-filtering, nonfile events are collected, leaving fewer rows for file events.

    • To avoid maintaining some kinds of event tables. If you disable a consumer, the server does not spend time maintaining destinations for that consumer. For example, if you do not care about event histories, you can disable the history table consumers to improve performance.

  • Post-filtering. This involves the use of WHERE clauses in queries that select information from Performance Schema tables, to specify which of the available events you want to see. Post-filtering is performed on a per-user basis because individual users select which of the available events are of interest.

    Reasons to use post-filtering:

    • To avoid making decisions for individual users about which event information is of interest.

    • To use the Performance Schema to investigate a performance issue when the restrictions to impose using pre-filtering are not known in advance.

The following sections provide more detail about pre-filtering and provide guidelines for naming instruments or consumers in filtering operations. For information about writing queries to retrieve information (post-filtering), see Section 24.4, “Performance Schema Queries”.

24.3.3 Event Pre-Filtering

Pre-filtering is done by the Performance Schema and has a global effect that applies to all users. Pre-filtering can be applied to either the producer or consumer stage of event processing:

  • To configure pre-filtering at the producer stage, several tables can be used:

    • setup_instruments indicates which instruments are available. An instrument disabled in this table produces no events regardless of the contents of the other production-related setup tables. An instrument enabled in this table is permitted to produce events, subject to the contents of the other tables.

    • setup_objects controls whether the Performance Schema monitors particular table and stored program objects.

    • threads indicates whether monitoring is enabled for each server thread.

    • setup_actors determines the initial monitoring state for new foreground threads.

  • To configure pre-filtering at the consumer stage, modify the setup_consumers table. This determines the destinations to which events are sent. setup_consumers also implicitly affects event production. If a given event will not be sent to any destination (that is, will not be consumed), the Performance Schema does not produce it.

Modifications to any of these tables affect monitoring immediately, with some exceptions:

  • Modifications to some instruments in the setup_instruments table are effective only at server startup; changing them at runtime has no effect. This affects primarily mutexes, conditions, and rwlocks in the server, although there may be other instruments for which this is true. This restriction is lifted as of MySQL 5.7.12.

  • Modifications to the setup_actors table affect only foreground threads created subsequent to the modification, not existing threads.

When you change the monitoring configuration, the Performance Schema does not flush the history tables. Events already collected remain in the current-events and history tables until displaced by newer events. If you disable instruments, you might need to wait a while before events for them are displaced by newer events of interest. Alternatively, use TRUNCATE TABLE to empty the history tables.

After making instrumentation changes, you might want to truncate the summary tables. Generally, the effect is to reset the summary columns to 0 or NULL, not to remove rows. This enables you to clear collected values and restart aggregation. That might be useful, for example, after you have made a runtime configuration change. Exceptions to this truncation behavior are noted in individual summary table sections.

The following sections describe how to use specific tables to control Performance Schema pre-filtering.

24.3.4 Pre-Filtering by Instrument

The setup_instruments table lists the available instruments:

mysql> SELECT * FROM setup_instruments;
+------------------------------------------------------------+---------+-------+
| NAME                                                       | ENABLED | TIMED |
+------------------------------------------------------------+---------+-------+
...
| wait/synch/mutex/sql/LOCK_global_read_lock                 | YES     | YES   |
| wait/synch/mutex/sql/LOCK_global_system_variables          | YES     | YES   |
| wait/synch/mutex/sql/LOCK_lock_db                          | YES     | YES   |
| wait/synch/mutex/sql/LOCK_manager                          | YES     | YES   |
...
| wait/synch/rwlock/sql/LOCK_grant                           | YES     | YES   |
| wait/synch/rwlock/sql/LOGGER::LOCK_logger                  | YES     | YES   |
| wait/synch/rwlock/sql/LOCK_sys_init_connect                | YES     | YES   |
| wait/synch/rwlock/sql/LOCK_sys_init_slave                  | YES     | YES   |
...
| wait/io/file/sql/binlog                                    | YES     | YES   |
| wait/io/file/sql/binlog_index                              | YES     | YES   |
| wait/io/file/sql/casetest                                  | YES     | YES   |
| wait/io/file/sql/dbopt                                     | YES     | YES   |
...

To control whether an instrument is enabled, set its ENABLED column to YES or NO. To configure whether to collect timing information for an enabled instrument, set its TIMED value to YES or NO. Setting the TIMED column affects Performance Schema table contents as described in Section 24.3.1, “Performance Schema Event Timing”.

Modifications to most setup_instruments rows affect monitoring immediately. For some instruments, modifications are effective only at server startup; changing them at runtime has no effect. This affects primarily mutexes, conditions, and rwlocks in the server, although there may be other instruments for which this is true.

The setup_instruments table provides the most basic form of control over event production. To further refine event production based on the type of object or thread being monitored, other tables may be used as described in Section 24.3.3, “Event Pre-Filtering”.

The following examples demonstrate possible operations on the setup_instruments table. These changes, like other pre-filtering operations, affect all users. Some of these queries use the LIKE operator and a pattern match instrument names. For additional information about specifying patterns to select instruments, see Section 24.3.9, “Naming Instruments or Consumers for Filtering Operations”.

  • Disable all instruments:

    mysql> UPDATE setup_instruments SET ENABLED = 'NO';
    

    Now no events will be collected.

  • Disable all file instruments, adding them to the current set of disabled instruments:

    mysql> UPDATE setup_instruments SET ENABLED = 'NO'
           WHERE NAME LIKE 'wait/io/file/%';
    
  • Disable only file instruments, enable all other instruments:

    mysql> UPDATE setup_instruments
           SET ENABLED = IF(NAME LIKE 'wait/io/file/%', 'NO', 'YES');
    
  • Enable all but those instruments in the mysys library:

    mysql> UPDATE setup_instruments
           SET ENABLED = CASE WHEN NAME LIKE '%/mysys/%' THEN 'YES' ELSE 'NO' END;
    
  • Disable a specific instrument:

    mysql> UPDATE setup_instruments SET ENABLED = 'NO'
           WHERE NAME = 'wait/synch/mutex/mysys/TMPDIR_mutex';
    
  • To toggle the state of an instrument, flip its ENABLED value:

    mysql> UPDATE setup_instruments
           SET ENABLED = IF(ENABLED = 'YES', 'NO', 'YES')
           WHERE NAME = 'wait/synch/mutex/mysys/TMPDIR_mutex';
    
  • Disable timing for all events:

    mysql> UPDATE setup_instruments SET TIMED = 'NO';
    

24.3.5 Pre-Filtering by Object

The setup_objects table controls whether the Performance Schema monitors particular table and stored program objects. The initial setup_objects contents look like this:

mysql> SELECT * FROM setup_objects;
+-------------+--------------------+-------------+---------+-------+
| OBJECT_TYPE | OBJECT_SCHEMA      | OBJECT_NAME | ENABLED | TIMED |
+-------------+--------------------+-------------+---------+-------+
| EVENT       | mysql              | %           | NO      | NO    |
| EVENT       | performance_schema | %           | NO      | NO    |
| EVENT       | information_schema | %           | NO      | NO    |
| EVENT       | %                  | %           | YES     | YES   |
| FUNCTION    | mysql              | %           | NO      | NO    |
| FUNCTION    | performance_schema | %           | NO      | NO    |
| FUNCTION    | information_schema | %           | NO      | NO    |
| FUNCTION    | %                  | %           | YES     | YES   |
| PROCEDURE   | mysql              | %           | NO      | NO    |
| PROCEDURE   | performance_schema | %           | NO      | NO    |
| PROCEDURE   | information_schema | %           | NO      | NO    |
| PROCEDURE   | %                  | %           | YES     | YES   |
| TABLE       | mysql              | %           | NO      | NO    |
| TABLE       | performance_schema | %           | NO      | NO    |
| TABLE       | information_schema | %           | NO      | NO    |
| TABLE       | %                  | %           | YES     | YES   |
| TRIGGER     | mysql              | %           | NO      | NO    |
| TRIGGER     | performance_schema | %           | NO      | NO    |
| TRIGGER     | information_schema | %           | NO      | NO    |
| TRIGGER     | %                  | %           | YES     | YES   |
+-------------+--------------------+-------------+---------+-------+

Modifications to the setup_objects table affect object monitoring immediately.

The OBJECT_TYPE column indicates the type of object to which a row applies. TABLE filtering affects table I/O events (wait/io/table/sql/handler instrument) and table lock events (wait/lock/table/sql/handler instrument).

The OBJECT_SCHEMA and OBJECT_NAME columns should contain a literal schema or object name, or '%' to match any name.

The ENABLED column indicates whether matching objects are monitored, and TIMED indicates whether to collect timing information. Setting the TIMED column affects Performance Schema table contents as described in Section 24.3.1, “Performance Schema Event Timing”.

The effect of the default object configuration is to instrument all objects except those in the mysql, INFORMATION_SCHEMA, and performance_schema databases. (Tables in the INFORMATION_SCHEMA database are not instrumented regardless of the contents of setup_objects; the row for information_schema.% simply makes this default explicit.)

When the Performance Schema checks for a match in setup_objects, it tries to find more specific matches first. For rows that match a given OBJECT_TYPE, the Performance Schema checks rows in this order:

  • Rows with OBJECT_SCHEMA='literal' and OBJECT_NAME='literal'.

  • Rows with OBJECT_SCHEMA='literal' and OBJECT_NAME='%'.

  • Rows with OBJECT_SCHEMA='%' and OBJECT_NAME='%'.

For example, with a table db1.t1, the Performance Schema looks in TABLE rows for a match for 'db1' and 't1', then for 'db1' and '%', then for '%' and '%'. The order in which matching occurs matters because different matching setup_objects rows can have different ENABLED and TIMED values.

For table-related events, the Performance Schema combines the contents of setup_objects with setup_instruments to determine whether to enable instruments and whether to time enabled instruments:

  • For tables that match a row in setup_objects, table instruments produce events only if ENABLED is YES in both setup_instruments and setup_objects.

  • The TIMED values in the two tables are combined, so that timing information is collected only when both values are YES.

For stored program objects, the Performance Schema takes the ENABLED and TIMED columns directly from the setup_objects row. There is no combining of values with setup_instruments.

Suppose that setup_objects contains the following TABLE rows that apply to db1, db2, and db3:

+-------------+---------------+-------------+---------+-------+
| OBJECT_TYPE | OBJECT_SCHEMA | OBJECT_NAME | ENABLED | TIMED |
+-------------+---------------+-------------+---------+-------+
| TABLE       | db1           | t1          | YES     | YES   |
| TABLE       | db1           | t2          | NO      | NO    |
| TABLE       | db2           | %           | YES     | YES   |
| TABLE       | db3           | %           | NO      | NO    |
| TABLE       | %             | %           | YES     | YES   |
+-------------+---------------+-------------+---------+-------+

If an object-related instrument in setup_instruments has an ENABLED value of NO, events for the object are not monitored. If the ENABLED value is YES, event monitoring occurs according to the ENABLED value in the relevant setup_objects row:

  • db1.t1 events are monitored

  • db1.t2 events are not monitored

  • db2.t3 events are monitored

  • db3.t4 events are not monitored

  • db4.t5 events are monitored

Similar logic applies for combining the TIMED columns from the setup_instruments and setup_objects tables to determine whether to collect event timing information.

If a persistent table and a temporary table have the same name, matching against setup_objects rows occurs the same way for both. It is not possible to enable monitoring for one table but not the other. However, each table is instrumented separately.

24.3.6 Pre-Filtering by Thread

The threads table contains a row for each server thread. Each row contains information about a thread and indicates whether monitoring is enabled for it. For the Performance Schema to monitor a thread, these things must be true:

  • The thread_instrumentation consumer in the setup_consumers table must be YES.

  • The threads.INSTRUMENTED column must be YES.

  • Monitoring occurs only for those thread events produced from instruments that are enabled in the setup_instruments table.

The threads table also indicates for each server thread whether to perform historical event logging. This includes wait, stage, statement, and transaction events and affects logging to these tables:

events_waits_history
events_waits_history_long
events_stages_history
events_stages_history_long
events_statements_history
events_statements_history_long
events_transactions_history
events_transactions_history_long

For historical event logging to occur, these things must be true:

  • The appropriate history-related consumers in the setup_consumers table must be enabled. For example, wait event logging in the events_waits_history and events_waits_history_long tables requires the corresponding events_waits_history and events_waits_history_long consumers to be YES.

  • The threads.HISTORY column must be YES.

  • Logging occurs only for those thread events produced from instruments that are enabled in the setup_instruments table.

For foreground threads (resulting from client connections), the initial values of the INSTRUMENTED and HISTORY columns in threads table rows are determined by whether the user account associated with a thread matches any row in the setup_actors table. The values come from the ENABLED and HISTORY columns of the matching setup_actors table row.

For background threads, there is no associated user. INSTRUMENTED and HISTORY are YES by default and setup_actors is not consulted.

The initial setup_actors contents look like this:

mysql> SELECT * FROM setup_actors;
+------+------+------+---------+---------+
| HOST | USER | ROLE | ENABLED | HISTORY |
+------+------+------+---------+---------+
| %    | %    | %    | YES     | YES     |
+------+------+------+---------+---------+

The HOST and USER columns should contain a literal host or user name, or '%' to match any name.

The ENABLED and HISTORY columns indicate whether to enable instrumentation and historical event logging for matching threads, subject to the other conditions described previously.

When the Performance Schema checks for a match for each new foreground thread in setup_actors, it tries to find more specific matches first, using the USER and HOST columns (ROLE is unused):

  • Rows with USER='literal' and HOST='literal'.

  • Rows with USER='literal' and HOST='%'.

  • Rows with USER='%' and HOST='literal'.

  • Rows with USER='%' and HOST='%'.

The order in which matching occurs matters because different matching setup_actors rows can have different USER and HOST values. This enables instrumenting and historical event logging to be applied selectively per host, user, or account (user and host combination), based on the ENABLED and HISTORY column values:

  • When the best match is a row with ENABLED=YES, the INSTRUMENTED value for the thread becomes YES. When the best match is a row with HISTORY=YES, the HISTORY value for the thread becomes YES.

  • When the best match is a row with ENABLED=NO, the INSTRUMENTED value for the thread becomes NO. When the best match is a row with HISTORY=NO, the HISTORY value for the thread becomes NO.

  • When no match is found, the INSTRUMENTED and HISTORY values for the thread become NO.

The ENABLED and HISTORY columns in setup_actors rows can be set to YES or NO independent of one another. This means you can enable instrumentation separately from whether you collect historical events.

Before MySQL 5.7.6, there is no ENABLED column. The INSTRUMENTED value for the thread becomes YES if any row matches, NO otherwise.

Before MySQL 5.7.8, there is no HISTORY column. The Performance Schema logs historical events either for all threads or no threads, depending on which history consumers are enabled or disabled.

By default, monitoring and historical event collection are enabled for all new foreground threads because the setup_actors table initially contains a row with '%' for both HOST and USER. To perform more limited matching such as to enable monitoring only for some foreground threads, you must change this row because it matches any connection, and add rows for more specific HOST/USER combinations.

Suppose that you modify setup_actors as follows:

UPDATE setup_actors SET ENABLED = 'NO', HISTORY = 'NO'
WHERE HOST = '%' AND USER = '%';
INSERT INTO setup_actors (HOST,USER,ROLE,ENABLED,HISTORY)
VALUES('localhost','joe','%','YES','YES');
INSERT INTO setup_actors (HOST,USER,ROLE,ENABLED,HISTORY)
VALUES('hosta.example.com','joe','%','YES','NO');
INSERT INTO setup_actors (HOST,USER,ROLE,ENABLED,HISTORY)
VALUES('%','sam','%','NO','YES');

The UPDATE statement changes the default match to disable instrumentation and historical event collection. The INSERT statements add rows for more specific matches.

Now the Performance Schema determines how to set the INSTRUMENTED and HISTORY values for new connection threads as follows:

  • If joe connects from the local host, the connection matches the first inserted row. The INSTRUMENTED and HISTORY values for the thread become YES.

  • If joe connects from hosta.example.com, the connection matches the second inserted row. The INSTRUMENTED value for the thread becomes YES and the HISTORY value becomes NO.

  • If joe connects from any other host, there is no match. The INSTRUMENTED and HISTORY values for the thread become NO.

  • If sam connects from any host, the connection matches the third inserted row. The INSTRUMENTED value for the thread becomes NO and the HISTORY value becomes YES.

  • For any other connection, the row with HOST and USER set to '%' matches. This row now has ENABLED and HISTORY set to NO, so the INSTRUMENTED and HISTORY values for the thread become NO.

Modifications to the setup_actors table affect only foreground threads created subsequent to the modification, not existing threads. To affect existing threads, modify the INSTRUMENTED and HISTORY columns of threads table rows.

24.3.7 Pre-Filtering by Consumer

The setup_consumers table lists the available consumer types and which are enabled:

mysql> SELECT * FROM setup_consumers;
+----------------------------------+---------+
| NAME                             | ENABLED |
+----------------------------------+---------+
| events_stages_current            | NO      |
| events_stages_history            | NO      |
| events_stages_history_long       | NO      |
| events_statements_current        | YES     |
| events_statements_history        | YES     |
| events_statements_history_long   | NO      |
| events_transactions_current      | NO      |
| events_transactions_history      | NO      |
| events_transactions_history_long | NO      |
| events_waits_current             | NO      |
| events_waits_history             | NO      |
| events_waits_history_long        | NO      |
| global_instrumentation           | YES     |
| thread_instrumentation           | YES     |
| statements_digest                | YES     |
+----------------------------------+---------+

Modify the setup_consumers table to affect pre-filtering at the consumer stage and determine the destinations to which events are sent. To enable or disable a consumer, set its ENABLED value to YES or NO.

Modifications to the setup_consumers table affect monitoring immediately.

If you disable a consumer, the server does not spend time maintaining destinations for that consumer. For example, if you do not care about historical event information, disable the history consumers:

mysql> UPDATE setup_consumers
       SET ENABLED = 'NO' WHERE NAME LIKE '%history%';

The consumer settings in the setup_consumers table form a hierarchy from higher levels to lower. The following principles apply:

  • Destinations associated with a consumer receive no events unless the Performance Schema checks the consumer and the consumer is enabled.

  • A consumer is checked only if all consumers it depends on (if any) are enabled.

  • If a consumer is not checked, or is checked but is disabled, other consumers that depend on it are not checked.

  • Dependent consumers may have their own dependent consumers.

  • If an event would not be sent to any destination, the Performance Schema does not produce it.

The following lists describe the available consumer values. For discussion of several representative consumer configurations and their effect on instrumentation, see Section 24.3.8, “Example Consumer Configurations”.

Global and Thread Consumers

  • global_instrumentation is the highest level consumer. If global_instrumentation is NO, it disables global instrumentation. All other settings are lower level and are not checked; it does not matter what they are set to. No global or per thread information is maintained and no individual events are collected in the current-events or event-history tables. If global_instrumentation is YES, the Performance Schema maintains information for global states and also checks the thread_instrumentation consumer.

  • thread_instrumentation is checked only if global_instrumentation is YES. Otherwise, if thread_instrumentation is NO, it disables thread-specific instrumentation and all lower-level settings are ignored. No information is maintained per thread and no individual events are collected in the current-events or event-history tables. If thread_instrumentation is YES, the Performance Schema maintains thread-specific information and also checks events_xxx_current consumers.

Wait Event Consumers

These consumers require both global_instrumentation and thread_instrumentation to be YES or they are not checked. If checked, they act as follows:

  • events_waits_current, if NO, disables collection of individual wait events in the events_waits_current table. If YES, it enables wait event collection and the Performance Schema checks the events_waits_history and events_waits_history_long consumers.

  • events_waits_history is not checked if event_waits_current is NO. Otherwise, an events_waits_history value of NO or YES disables or enables collection of wait events in the events_waits_history table.

  • events_waits_history_long is not checked if event_waits_current is NO. Otherwise, an events_waits_history_long value of NO or YES disables or enables collection of wait events in the events_waits_history_long table.

Stage Event Consumers

These consumers require both global_instrumentation and thread_instrumentation to be YES or they are not checked. If checked, they act as follows:

  • events_stages_current, if NO, disables collection of individual stage events in the events_stages_current table. If YES, it enables stage event collection and the Performance Schema checks the events_stages_history and events_stages_history_long consumers.

  • events_stages_history is not checked if event_stages_current is NO. Otherwise, an events_stages_history value of NO or YES disables or enables collection of stage events in the events_stages_history table.

  • events_stages_history_long is not checked if event_stages_current is NO. Otherwise, an events_stages_history_long value of NO or YES disables or enables collection of stage events in the events_stages_history_long table.

Statement Event Consumers

These consumers require both global_instrumentation and thread_instrumentation to be YES or they are not checked. If checked, they act as follows:

  • events_statements_current, if NO, disables collection of individual statement events in the events_statements_current table. If YES, it enables statement event collection and the Performance Schema checks the events_statements_history and events_statements_history_long consumers.

  • events_statements_history is not checked if events_statements_current is NO. Otherwise, an events_statements_history value of NO or YES disables or enables collection of statement events in the events_statements_history table.

  • events_statements_history_long is not checked if events_statements_current is NO. Otherwise, an events_statements_history_long value of NO or YES disables or enables collection of statement events in the events_statements_history_long table.

Transaction Event Consumers

These consumers require both global_instrumentation and thread_instrumentation to be YES or they are not checked. If checked, they act as follows:

  • events_transactions_current, if NO, disables collection of individual transaction events in the events_transactions_current table. If YES, it enables transaction event collection and the Performance Schema checks the events_transactions_history and events_transactions_history_long consumers.

  • events_transactions_history is not checked if events_transactions_current is NO. Otherwise, an events_transactions_history value of NO or YES disables or enables collection of transaction events in the events_transactions_history table.

  • events_transactions_history_long is not checked if events_transactions_current is NO. Otherwise, an events_transactions_history_long value of NO or YES disables or enables collection of transaction events in the events_transactions_history_long table.

Statement Digest Consumer

This consumer requires global_instrumentation to be YES or it is not checked. There is no dependency on the statement event consumers, so you can obtain statistics per digest without having to collect statistics in events_statements_current, which is advantageous in terms of overhead. Conversely, you can get detailed statements in events_statements_current without digests (the DIGEST and DIGEST_TEXT columns will be NULL).

24.3.8 Example Consumer Configurations

The consumer settings in the setup_consumers table form a hierarchy from higher levels to lower. The following discussion describes how consumers work, showing specific configurations and their effects as consumer settings are enabled progressively from high to low. The consumer values shown are representative. The general principles described here apply to other consumer values that may be available.

The configuration descriptions occur in order of increasing functionality and overhead. If you do not need the information provided by enabling lower-level settings, disable them and the Performance Schema will execute less code on your behalf and you will have less information to sift through.

The setup_consumers table contains the following hierarchy of values:

global_instrumentation
 thread_instrumentation
   events_waits_current
     events_waits_history
     events_waits_history_long
   events_stages_current
     events_stages_history
     events_stages_history_long
   events_statements_current
     events_statements_history
     events_statements_history_long
   events_transactions_current
     events_transactions_history
     events_transactions_history_long
 statements_digest
Note

In the consumer hierarchy, the consumers for waits, stages, statements, and transactions are all at the same level. This differs from the event nesting hierarchy, for which wait events nest within stage events, which nest within statement events, which nest within transaction events.

If a given consumer setting is NO, the Performance Schema disables the instrumentation associated with the consumer and ignores all lower-level settings. If a given setting is YES, the Performance Schema enables the instrumentation associated with it and checks the settings at the next lowest level. For a description of the rules for each consumer, see Section 24.3.7, “Pre-Filtering by Consumer”.

For example, if global_instrumentation is enabled, thread_instrumentation is checked. If thread_instrumentation is enabled, the events_xxx_current consumers are checked. If of these events_waits_current is enabled, events_waits_history and events_waits_history_long are checked.

Each of the following configuration descriptions indicates which setup elements the Performance Schema checks and which output tables it maintains (that is, for which tables it collects information).

No Instrumentation

Server configuration state:

mysql> SELECT * FROM setup_consumers;
+---------------------------+---------+
| NAME                      | ENABLED |
+---------------------------+---------+
| global_instrumentation    | NO      |
...
+---------------------------+---------+

In this configuration, nothing is instrumented.

Setup elements checked:

Output tables maintained:

  • None

Global Instrumentation Only

Server configuration state:

mysql> SELECT * FROM setup_consumers;
+---------------------------+---------+
| NAME                      | ENABLED |
+---------------------------+---------+
| global_instrumentation    | YES     |
| thread_instrumentation    | NO      |
...
+---------------------------+---------+

In this configuration, instrumentation is maintained only for global states. Per-thread instrumentation is disabled.

Additional setup elements checked, relative to the preceding configuration:

Additional output tables maintained, relative to the preceding configuration:

Global and Thread Instrumentation Only

Server configuration state:

mysql> SELECT * FROM setup_consumers;
+----------------------------------+---------+
| NAME                             | ENABLED |
+----------------------------------+---------+
| global_instrumentation           | YES     |
| thread_instrumentation           | YES     |
| events_waits_current             | NO      |
...
| events_stages_current            | NO      |
...
| events_statements_current        | NO      |
...
| events_transactions_current      | NO      |
...
+----------------------------------+---------+

In this configuration, instrumentation is maintained globally and per thread. No individual events are collected in the current-events or event-history tables.

Additional setup elements checked, relative to the preceding configuration:

  • Table setup_consumers, consumers events_xxx_current, where xxx is waits, stages, statements, transactions

  • Table setup_actors

  • Column threads.instrumented

Additional output tables maintained, relative to the preceding configuration:

  • events_xxx_summary_by_yyy_by_event_name, where xxx is waits, stages, statements, transactions; and yyy is thread, user, host, account

Global, Thread, and Current-Event Instrumentation

Server configuration state:

mysql> SELECT * FROM setup_consumers;
+----------------------------------+---------+
| NAME                             | ENABLED |
+----------------------------------+---------+
| global_instrumentation           | YES     |
| thread_instrumentation           | YES     |
| events_waits_current             | YES     |
| events_waits_history             | NO      |
| events_waits_history_long        | NO      |
| events_stages_current            | YES     |
| events_stages_history            | NO      |
| events_stages_history_long       | NO      |
| events_statements_current        | YES     |
| events_statements_history        | YES     |
| events_statements_history_long   | NO      |
| events_transactions_current      | YES     |
| events_transactions_history      | YES     |
| events_transactions_history_long | NO      |
...
+----------------------------------+---------+

In this configuration, instrumentation is maintained globally and per thread. Individual events are collected in the current-events table, but not in the event-history tables.

Additional setup elements checked, relative to the preceding configuration:

  • Consumers events_xxx_history, where xxx is waits, stages, statements, transactions

  • Consumers events_xxx_history_long, where xxx is waits, stages, statements, transactions

Additional output tables maintained, relative to the preceding configuration:

  • events_xxx_current, where xxx is waits, stages, statements, transactions

Global, Thread, Current-Event, and Event-History instrumentation

The preceding configuration collects no event history because the events_xxx_history and events_xxx_history_long consumers are disabled. Those consumers can be enabled separately or together to collect event history per thread, globally, or both.

This configuration collects event history per thread, but not globally:

mysql> SELECT * FROM setup_consumers;
+----------------------------------+---------+
| NAME                             | ENABLED |
+----------------------------------+---------+
| global_instrumentation           | YES     |
| thread_instrumentation           | YES     |
| events_waits_current             | YES     |
| events_waits_history             | YES     |
| events_waits_history_long        | NO      |
| events_stages_current            | YES     |
| events_stages_history            | YES     |
| events_stages_history_long       | NO      |
| events_statements_current        | YES     |
| events_statements_history        | YES     |
| events_statements_history_long   | NO      |
| events_transactions_current      | YES     |
| events_transactions_history      | YES     |
| events_transactions_history_long | NO      |
...
+----------------------------------+---------+

Event-history tables maintained for this configuration:

  • events_xxx_history, where xxx is waits, stages, statements, transactions

This configuration collects event history globally, but not per thread:

mysql> SELECT * FROM setup_consumers;
+----------------------------------+---------+
| NAME                             | ENABLED |
+----------------------------------+---------+
| global_instrumentation           | YES     |
| thread_instrumentation           | YES     |
| events_waits_current             | YES     |
| events_waits_history             | NO      |
| events_waits_history_long        | YES     |
| events_stages_current            | YES     |
| events_stages_history            | NO      |
| events_stages_history_long       | YES     |
| events_statements_current        | YES     |
| events_statements_history        | YES     |
| events_statements_history_long   | YES     |
| events_transactions_current      | YES     |
| events_transactions_history      | YES     |
| events_transactions_history_long | YES     |
...
+----------------------------------+---------+

Event-history tables maintained for this configuration:

  • events_xxx_history_long, where xxx is waits, stages, statements, transactions

This configuration collects event history per thread and globally:

mysql> SELECT * FROM setup_consumers;
+----------------------------------+---------+
| NAME                             | ENABLED |
+----------------------------------+---------+
| global_instrumentation           | YES     |
| thread_instrumentation           | YES     |
| events_waits_current             | YES     |
| events_waits_history             | YES     |
| events_waits_history_long        | YES     |
| events_stages_current            | YES     |
| events_stages_history            | YES     |
| events_stages_history_long       | YES     |
| events_statements_current        | YES     |
| events_statements_history        | YES     |
| events_statements_history_long   | YES     |
| events_transactions_current      | YES     |
| events_transactions_history      | YES     |
| events_transactions_history_long | YES     |
...
+----------------------------------+---------+

Event-history tables maintained for this configuration:

  • events_xxx_history, where xxx is waits, stages, statements, transactions

  • events_xxx_history_long, where xxx is waits, stages, statements, transactions

24.3.9 Naming Instruments or Consumers for Filtering Operations

Names given for filtering operations can be as specific or general as required. To indicate a single instrument or consumer, specify its name in full:

mysql> UPDATE setup_instruments
       SET ENABLED = 'NO'
       WHERE NAME = 'wait/synch/mutex/myisammrg/MYRG_INFO::mutex';

mysql> UPDATE setup_consumers
       SET ENABLED = 'NO' WHERE NAME = 'events_waits_current';

To specify a group of instruments or consumers, use a pattern that matches the group members:

mysql> UPDATE setup_instruments
       SET ENABLED = 'NO'
       WHERE NAME LIKE 'wait/synch/mutex/%';

mysql> UPDATE setup_consumers
       SET ENABLED = 'NO' WHERE NAME LIKE '%history%';

If you use a pattern, it should be chosen so that it matches all the items of interest and no others. For example, to select all file I/O instruments, it is better to use a pattern that includes the entire instrument name prefix:

... WHERE NAME LIKE 'wait/io/file/%';

A pattern of '%/file/%' will match other instruments that have a component of '/file/' anywhere in the name. Even less suitable is the pattern '%file%' because it will match instruments with 'file' anywhere in the name, such as wait/synch/mutex/sql/LOCK_des_key_file.

To check which instrument or consumer names a pattern matches, perform a simple test:

mysql> SELECT NAME FROM setup_instruments WHERE NAME LIKE 'pattern';

mysql> SELECT NAME FROM setup_consumers WHERE NAME LIKE 'pattern';

For information about the types of names that are supported, see Section 24.5, “Performance Schema Instrument Naming Conventions”.

24.3.10 Determining What Is Instrumented

It is always possible to determine what instruments the Performance Schema includes by checking the setup_instruments table. For example, to see what file-related events are instrumented for the InnoDB storage engine, use this query:

mysql> SELECT * FROM setup_instruments WHERE NAME LIKE 'wait/io/file/innodb/%';
+--------------------------------------+---------+-------+
| NAME                                 | ENABLED | TIMED |
+--------------------------------------+---------+-------+
| wait/io/file/innodb/innodb_data_file | YES     | YES   |
| wait/io/file/innodb/innodb_log_file  | YES     | YES   |
| wait/io/file/innodb/innodb_temp_file | YES     | YES   |
+--------------------------------------+---------+-------+

An exhaustive description of precisely what is instrumented is not given in this documentation, for several reasons:

  • What is instrumented is the server code. Changes to this code occur often, which also affects the set of instruments.

  • It is not practical to list all the instruments because there are hundreds of them.

  • As described earlier, it is possible to find out by querying the setup_instruments table. This information is always up to date for your version of MySQL, also includes instrumentation for instrumented plugins you might have installed that are not part of the core server, and can be used by automated tools.

24.4 Performance Schema Queries

Pre-filtering limits which event information is collected and is independent of any particular user. By contrast, post-filtering is performed by individual users through the use of queries with appropriate WHERE clauses that restrict what event information to select from the events available after pre-filtering has been applied.

In Section 24.3.3, “Event Pre-Filtering”, an example showed how to pre-filter for file instruments. If the event tables contain both file and nonfile information, post-filtering is another way to see information only for file events. Add a WHERE clause to queries to restrict event selection appropriately:

mysql> SELECT THREAD_ID, NUMBER_OF_BYTES
       FROM events_waits_history
       WHERE EVENT_NAME LIKE 'wait/io/file/%'
       AND NUMBER_OF_BYTES IS NOT NULL;
+-----------+-----------------+
| THREAD_ID | NUMBER_OF_BYTES |
+-----------+-----------------+
|        11 |              66 |
|        11 |              47 |
|        11 |             139 |
|         5 |              24 |
|         5 |             834 |
+-----------+-----------------+

24.5 Performance Schema Instrument Naming Conventions

An instrument name consists of a sequence of components separated by '/' characters. Example names:

wait/io/file/myisam/log
wait/io/file/mysys/charset
wait/lock/table/sql/handler
wait/synch/cond/mysys/COND_alarm
wait/synch/cond/sql/BINLOG::update_cond
wait/synch/mutex/mysys/BITMAP_mutex
wait/synch/mutex/sql/LOCK_delete
wait/synch/rwlock/sql/Query_cache_query::lock
stage/sql/closing tables
stage/sql/Sorting result
statement/com/Execute
statement/com/Query
statement/sql/create_table
statement/sql/lock_tables

The instrument name space has a tree-like structure. The components of an instrument name from left to right provide a progression from more general to more specific. The number of components a name has depends on the type of instrument.

The interpretation of a given component in a name depends on the components to the left of it. For example, myisam appears in both of the following names, but myisam in the first name is related to file I/O, whereas in the second it is related to a synchronization instrument:

wait/io/file/myisam/log
wait/synch/cond/myisam/MI_SORT_INFO::cond

Instrument names consist of a prefix with a structure defined by the Performance Schema implementation and a suffix defined by the developer implementing the instrument code. The top-level component of an instrument prefix indicates the type of instrument. This component also determines which event timer in the setup_timers table applies to the instrument. For the prefix part of instrument names, the top level indicates the type of instrument.

The suffix part of instrument names comes from the code for the instruments themselves. Suffixes may include levels such as these:

  • A name for the major component (a server module such as myisam, innodb, mysys, or sql) or a plugin name.

  • The name of a variable in the code, in the form XXX (a global variable) or CCC::MMM (a member MMM in class CCC). Examples: COND_thread_cache, THR_LOCK_myisam, BINLOG::LOCK_index.

Top-Level Instrument Components

  • idle: An instrumented idle event. This instrument has no further components.

  • memory: An instrumented memory event.

  • stage: An instrumented stage event.

  • statement: An instrumented statement event.

  • transaction: An instrumented transaction event. This instrument has no further components.

  • wait: An instrumented wait event.

Idle Instrument Components

The idle instrument is used for idle events, which The Performance Schema generates as discussed in the description of the socket_instances.STATE column in Section 24.10.3.5, “The socket_instances Table”.

Memory Instrument Components

Most memory instrumentation is disabled by default, and can be enabled or disabled dynamically by updating the ENABLED column of the relevant instruments in the setup_instruments table. Memory instruments have names of the form memory/code_area/instrument_name where code_area is a value such as sql or myisam, and instrument_name is the instrument detail.

Instruments named with the prefix memory/performance_schema/ expose how much memory is allocated for internal buffers in the Performance Schema. The memory/performance_schema/ instruments are built in, always enabled, and cannot be disabled at startup or runtime. The built-in memory instruments are displayed only in the memory_summary_global_by_event_name table. For more information, see Section 24.15, “The Performance Schema Memory-Allocation Model”.

Stage Instrument Components

Stage instruments have names of the form stage/code_area/stage_name, where code_area is a value such as sql or myisam, and stage_name indicates the stage of statement processing, such as Sorting result or Sending data. Stages correspond to the thread states displayed by SHOW PROCESSLIST or that are visible in the INFORMATION_SCHEMA.PROCESSLIST table.

Statement Instrument Components

  • statement/abstract/*: An abstract instrument for statement operations. Abstract instruments are used during the early stages of statement classification before the exact statement type is known, then changed to a more specific statement instrument when the type is known. For a description of this process, see Section 24.10.6, “Performance Schema Statement Event Tables”.

  • statement/com: An instrumented command operation. These have names corresponding to COM_xxx operations (see the mysql_com.h header file and sql/sql_parse.cc. For example, the statement/com/Connect and statement/com/Init DB instruments correspond to the COM_CONNECT and COM_INIT_DB commands.

  • statement/scheduler/event: A single instrument to track all events executed by the Event Scheduler. This instrument comes into play when a scheduled event begins executing.

  • statement/sp: An instrumented internal instruction executed by a stored program. For example, the statement/sp/cfetch and statement/sp/freturn instruments are used cursor fetch and function return instructions.

  • statement/sql: An instrumented SQL statement operation. For example, the statement/sql/create_db and statement/sql/select instruments are used for CREATE DATABASE and SELECT statements.

Wait Instrument Components

  • wait/io

    An instrumented I/O operation.

    • wait/io/file

      An instrumented file I/O operation. For files, the wait is the time waiting for the file operation to complete (for example, a call to fwrite()). Due to caching, the physical file I/O on the disk might not happen within this call.

    • wait/io/socket

      An instrumented socket operation. Socket instruments have names of the form wait/io/socket/sql/socket_type. The server has a listening socket for each network protocol that it supports. The instruments associated with listening sockets for TCP/IP or Unix socket file connections have a socket_type value of server_tcpip_socket or server_unix_socket, respectively. When a listening socket detects a connection, the server transfers the connection to a new socket managed by a separate thread. The instrument for the new connection thread has a socket_type value of client_connection.

    • wait/io/table

      An instrumented table I/O operation. These include row-level accesses to persistent base tables or temporary tables. Operations that affect rows are fetch, insert, update, and delete. For a view, waits are associated with base tables referenced by the view.

      Unlike most waits, a table I/O wait can include other waits. For example, table I/O might include file I/O or memory operations. Thus, events_waits_current for a table I/O wait usually has two rows. For more information, see Section 24.7, “Performance Schema Atom and Molecule Events”.

      Some row operations might cause multiple table I/O waits. For example, an insert might activate a trigger that causes an update.

  • wait/lock

    An instrumented lock operation.

    • wait/lock/table

      An instrumented table lock operation.

    • wait/lock/metadata/sql/mdl

      An instrumented metadata lock operation (disabled by default).

  • wait/synch

    An instrumented synchronization object. For synchronization objects, the TIMER_WAIT time includes the amount of time blocked while attempting to acquire a lock on the object, if any.

    • wait/synch/cond

      A condition is used by one thread to signal to other threads that something they were waiting for has happened. If a single thread was waiting for a condition, it can wake up and proceed with its execution. If several threads were waiting, they can all wake up and compete for the resource for which they were waiting.

    • wait/synch/mutex

      A mutual exclusion object used to permit access to a resource (such as a section of executable code) while preventing other threads from accessing the resource.

    • wait/synch/rwlock

      A read/write lock object used to lock a specific variable for access while preventing its use by other threads. A shared read lock can be acquired simultaneously by multiple threads. An exclusive write lock can be acquired by only one thread at a time.

    • wait/synch/sxlock

      A shared-exclusive (SX) lock is a type of rwlock lock object that provides write access to a common resource while permitting inconsistent reads by other threads. sxlocks were introduced in MySQL 5.7 to optimize concurrency and improve scalability for read-write workloads.

24.6 Performance Schema Status Monitoring

There are several status variables associated with the Performance Schema:

mysql> SHOW STATUS LIKE 'perf%';
+-----------------------------------------------+-------+
| Variable_name                                 | Value |
+-----------------------------------------------+-------+
| Performance_schema_accounts_lost              | 0     |
| Performance_schema_cond_classes_lost          | 0     |
| Performance_schema_cond_instances_lost        | 0     |
| Performance_schema_digest_lost                | 0     |
| Performance_schema_file_classes_lost          | 0     |
| Performance_schema_file_handles_lost          | 0     |
| Performance_schema_file_instances_lost        | 0     |
| Performance_schema_hosts_lost                 | 0     |
| Performance_schema_locker_lost                | 0     |
| Performance_schema_memory_classes_lost        | 0     |
| Performance_schema_metadata_lock_lost         | 0     |
| Performance_schema_mutex_classes_lost         | 0     |
| Performance_schema_mutex_instances_lost       | 0     |
| Performance_schema_nested_statement_lost      | 0     |
| Performance_schema_program_lost               | 0     |
| Performance_schema_rwlock_classes_lost        | 0     |
| Performance_schema_rwlock_instances_lost      | 0     |
| Performance_schema_session_connect_attrs_lost | 0     |
| Performance_schema_socket_classes_lost        | 0     |
| Performance_schema_socket_instances_lost      | 0     |
| Performance_schema_stage_classes_lost         | 0     |
| Performance_schema_statement_classes_lost     | 0     |
| Performance_schema_table_handles_lost         | 0     |
| Performance_schema_table_instances_lost       | 0     |
| Performance_schema_thread_classes_lost        | 0     |
| Performance_schema_thread_instances_lost      | 0     |
| Performance_schema_users_lost                 | 0     |
+-----------------------------------------------+-------+

The Performance Schema status variables provide information about instrumentation that could not be loaded or created due to memory constraints. Names for these variables have several forms:

  • Performance_schema_xxx_classes_lost indicates how many instruments of type xxx could not be loaded.

  • Performance_schema_xxx_instances_lost indicates how many instances of object type xxx could not be created.

  • Performance_schema_xxx_handles_lost indicates how many instances of object type xxx could not be opened.

  • Performance_schema_locker_lost indicates how many events are lost or not recorded.

For example, if a mutex is instrumented in the server source but the server cannot allocate memory for the instrumentation at runtime, it increments Performance_schema_mutex_classes_lost. The mutex still functions as a synchronization object (that is, the server continues to function normally), but performance data for it will not be collected. If the instrument can be allocated, it can be used for initializing instrumented mutex instances. For a singleton mutex such as a global mutex, there will be only one instance. Other mutexes have an instance per connection, or per page in various caches and data buffers, so the number of instances varies over time. Increasing the maximum number of connections or the maximum size of some buffers will increase the maximum number of instances that might be allocated at once. If the server cannot create a given instrumented mutex instance, it increments Performance_schema_mutex_instances_lost.

Suppose that the following conditions hold:

  • The server was started with the --performance_schema_max_mutex_classes=200 option and thus has room for 200 mutex instruments.

  • 150 mutex instruments have been loaded already.

  • The plugin named plugin_a contains 40 mutex instruments.

  • The plugin named plugin_b contains 20 mutex instruments.

The server allocates mutex instruments for the plugins depending on how many they need and how many are available, as illustrated by the following sequence of statements:

INSTALL PLUGIN plugin_a

The server now has 150+40 = 190 mutex instruments.

UNINSTALL PLUGIN plugin_a;

The server still has 190 instruments. All the historical data generated by the plugin code is still available, but new events for the instruments are not collected.

INSTALL PLUGIN plugin_a;

The server detects that the 40 instruments are already defined, so no new instruments are created, and previously assigned internal memory buffers are reused. The server still has 190 instruments.

INSTALL PLUGIN plugin_b;

The server has room for 200-190 = 10 instruments (in this case, mutex classes), and sees that the plugin contains 20 new instruments. 10 instruments are loaded, and 10 are discarded or lost. The Performance_schema_mutex_classes_lost indicates the number of instruments (mutex classes) lost:

mysql> SHOW STATUS LIKE "perf%mutex_classes_lost";
+---------------------------------------+-------+
| Variable_name                         | Value |
+---------------------------------------+-------+
| Performance_schema_mutex_classes_lost | 10    |
+---------------------------------------+-------+
1 row in set (0.10 sec)

The instrumentation still works and collects (partial) data for plugin_b.

When the server cannot create a mutex instrument, these results occur:

The pattern just described applies to all types of instruments, not just mutexes.

A value of Performance_schema_mutex_classes_lost greater than 0 can happen in two cases:

  • To save a few bytes of memory, you start the server with --performance_schema_max_mutex_classes=N, where N is less than the default value. The default value is chosen to be sufficient to load all the plugins provided in the MySQL distribution, but this can be reduced if some plugins are never loaded. For example, you might choose not to load some of the storage engines in the distribution.

  • You load a third-party plugin that is instrumented for the Performance Schema but do not allow for the plugin's instrumentation memory requirements when you start the server. Because it comes from a third party, the instrument memory consumption of this engine is not accounted for in the default value chosen for performance_schema_max_mutex_classes.

    If the server has insufficient resources for the plugin's instruments and you do not explicitly allocate more using --performance_schema_max_mutex_classes=N, loading the plugin leads to starvation of instruments.

If the value chosen for performance_schema_max_mutex_classes is too small, no error is reported in the error log and there is no failure at runtime. However, the content of the tables in the performance_schema database will miss events. The Performance_schema_mutex_classes_lost status variable is the only visible sign to indicate that some events were dropped internally due to failure to create instruments.

If an instrument is not lost, it is known to the Performance Schema, and is used when instrumenting instances. For example, wait/synch/mutex/sql/LOCK_delete is the name of a mutex instrument in the setup_instruments table. This single instrument is used when creating a mutex in the code (in THD::LOCK_delete) however many instances of the mutex are needed as the server runs. In this case, LOCK_delete is a mutex that is per connection (THD), so if a server has 1000 connections, there are 1000 threads, and 1000 instrumented LOCK_delete mutex instances (THD::LOCK_delete).

If the server does not have room for all these 1000 instrumented mutexes (instances), some mutexes are created with instrumentation, and some are created without instrumentation. If the server can create only 800 instances, 200 instances are lost. The server continues to run, but increments Performance_schema_mutex_instances_lost by 200 to indicate that instances could not be created.

A value of Performance_schema_mutex_instances_lost greater than 0 can happen when the code initializes more mutexes at runtime than were allocated for --performance_schema_max_mutex_instances=N.

The bottom line is that if SHOW STATUS LIKE 'perf%' says that nothing was lost (all values are zero), the Performance Schema data is accurate and can be relied upon. If something was lost, the data is incomplete, and the Performance Schema could not record everything given the insufficient amount of memory it was given to use. In this case, the specific Performance_schema_xxx_lost variable indicates the problem area.

It might be appropriate in some cases to cause deliberate instrument starvation. For example, if you do not care about performance data for file I/O, you can start the server with all Performance Schema parameters related to file I/O set to 0. No memory will be allocated for file-related classes, instances, or handles, and all file events will be lost.

Use SHOW ENGINE PERFORMANCE_SCHEMA STATUS to inspect the internal operation of the Performance Schema code:

mysql> SHOW ENGINE PERFORMANCE_SCHEMA STATUS\G
...
*************************** 3. row ***************************
  Type: performance_schema
  Name: events_waits_history.size
Status: 76
*************************** 4. row ***************************
  Type: performance_schema
  Name: events_waits_history.count
Status: 10000
*************************** 5. row ***************************
  Type: performance_schema
  Name: events_waits_history.memory
Status: 760000
...
*************************** 57. row ***************************
  Type: performance_schema
  Name: performance_schema.memory
Status: 26459600
...

This statement is intended to help the DBA understand the effects that different Performance Schema options have on memory requirements. For a description of the field meanings, see Section 14.7.5.15, “SHOW ENGINE Syntax”.

24.7 Performance Schema Atom and Molecule Events

For a table I/O event, there are usually two rows in events_waits_current, not one. For example, a row fetch might result in rows like this:

Row# EVENT_NAME                 TIMER_START TIMER_END
---- ----------                 ----------- ---------
   1 wait/io/file/myisam/dfile        10001 10002
   2 wait/io/table/sql/handler        10000 NULL

The row fetch causes a file read. In the example, the table I/O fetch event started before the file I/O event but has not finished (its TIMER_END value is NULL). The file I/O event is nested within the table I/O event.

This occurs because, unlike other atomic wait events such as for mutexes or file I/O, table I/O events are molecular and include (overlap with) other events. In events_waits_current, the table I/O event usually has two rows:

  • One row for the most recent table I/O wait event

  • One row for the most recent wait event of any kind

Usually, but not always, the of any kind wait event differs from the table I/O event. As each subsidiary event completes, it disappears from events_waits_current. At this point, and until the next subsidiary event begins, the table I/O wait is also the most recent wait of any kind.

24.8 Performance Schema Statement Digests

The MySQL server is capable of maintaining statement digest information. The digesting process converts an SQL statement to normalized form and computes a hash value for the result. Normalization permits statements that are similar to be grouped and summarized to expose information about the types of statements the server is executing and how often they occur. This section describes how statement normalizing occurs and how it can be useful.

Note

Before MySQL 5.7.4, statement digesting was a function of the Performance Schema. As of 5.7.4, digesting occurs at the SQL level regardless of whether the Performance Schema is available, so that other server functions such as query rewrite plugins have access to statement digests.

In the Performance Schema, statement digesting involves these components:

  • A statement_digest consumer in the setup_consumers table controls whether the Performance Schema maintains digest information.

  • The statement event tables (events_statements_current, events_statements_history, and events_statements_history_long) have columns that contain digests and the corresponding digest hash values:

    • DIGEST_TEXT is the text of the normalized statement digest.

    • DIGEST is the digest MD5 hash value.

    The maximum space available for digest computation is 1024 bytes by default. This value can be changed at server startup by setting the performance_schema_max_digest_length system variable. In MySQL 5.7.6 and 5.7.7, use max_digest_length instead. Before 5.7.6, the value cannot be changed.

  • The statement event tables also have a SQL_TEXT column that contains the original SQL statement. The maximum space available for statement display is 1024 bytes by default. As of MySQL 5.7.6, this value can be changed at server startup by setting the performance_schema_max_sql_text_length system variable. Before 5.7.6, the value cannot be changed.

  • An events_statements_summary_by_digest table provides aggregated statement digest information.

Statement normalization transforms the statement text to a more standardized digest string representation that preserves the general statement structure while removing information not essential to the structure:

  • Object identifiers such as database and table names are preserved.

  • Literal values are converted to parameter markers. A normalized statement does not retain information such as names, passwords, dates, and so forth.

  • Comments are removed and whitespace is adjusted.

Consider these statements:

SELECT * FROM orders WHERE customer_id=10 AND quantity>20
SELECT * FROM orders WHERE customer_id = 20 AND quantity > 100

To normalize these statements, the Performance Schema replaces data values by ? and adjusts whitespace. Both statements yield the same normalized form and thus are considered the same:

SELECT * FROM orders WHERE customer_id = ? AND quantity > ?

The normalized statement contains less information but is still representative of the original statement. Other similar statements that have different comparison values have the same normalized form.

Now consider these statements:

SELECT * FROM customers WHERE customer_id = 1000
SELECT * FROM orders WHERE customer_id = 1000

In this case, the statements are not the same. The object identifiers differ, so the statements yield different normalized forms:

SELECT * FROM customers WHERE customer_id = ?
SELECT * FROM orders WHERE customer_id = ?

If normalization produces a statement that exceeds the space available in the digest buffer, the text ends with .... Long statements that differ only in the part that occurs following the ... are considered to be the same. Consider these statements:

SELECT * FROM mytable WHERE cola = 10 AND colb = 20
SELECT * FROM mytable WHERE cola = 10 AND colc = 20

If the cutoff happens to be right after the AND, both statements have this normalized form:

SELECT * FROM mytable WHERE cola = ? AND ...

In this case, the difference in the second column name is lost and both statements are considered the same.

For each normalized statement, the Performance Schema computes a hash digest value and stores the statement and its MD5 hash value in the DIGEST_TEXT and DIGEST columns of the statement event tables (events_statements_current, events_statements_history, and events_statements_history_long). In addition, statement digests are summarized in the events_statements_summary_by_digest table, which aggregates information for statements that have the same SCHEMA_NAME and DIGEST values. The Performance Schema uses MD5 hash values because they are fast to compute and have a favorable statistical distribution that minimizes collisions.

The statement digest summary table provides a profile of the statements executed by the server. It shows what kinds of statements an application is executing and how often. An application developer can use this information together with other information in the table to assess the application's performance characteristics. For example, table columns that show wait times, lock times, or index use may highlight types of queries that are inefficient. This gives the developer insight into which parts of the application need attention.

The events_statements_summary_by_digest summary table has a fixed size. When it becomes full, statements that have SCHEMA_NAME and DIGEST values not matching existing values in the table are grouped in a special row with SCHEMA_NAME and DIGEST set to NULL. This permits all statements to be counted. However, if the special row accounts for a significant percentage of the statements executed, it might be desirable to increase the size of the summary table by setting the performance_schema_digests_size system variable to a larger value at server startup. If no performance_schema_digests_size value is given, the Performance Schema estimates the value to use at startup.

The performance_schema_max_digest_length system variable determines the maximum number of bytes available in the digest buffer for digest computation. However, the display length of statement digests may be longer than the available buffer size due to internal encoding of statement components such as keywords and literal values. Consequently, values selected from the DIGEST_TEXT column of statement event tables may appear to exceed the performance_schema_max_digest_length value.

For applications that generate very long statements that differ only at the end, increasing performance_schema_max_digest_length enables computation of digests that distinguish statements that would otherwise aggregate to the same digest. Conversely, decreasing performance_schema_max_digest_length causes the server to devote less memory to digest storage but increases the likelihood of longer statements aggregating to the same digest. Administrators should keep in mind that larger values result in correspondingly increased memory requirements, particularly for workloads that involve large numbers of simultaneous sessions (performance_schema_max_digest_length bytes are allocated per session).

To assess the amount of memory used for SQL statement storage and digest computation, use the SHOW ENGINE PERFORMANCE_SCHEMA STATUS statement, or monitor these instruments:

mysql> SELECT NAME FROM setup_instruments
       WHERE NAME LIKE '%.sqltext';
+------------------------------------------------------------------+
| NAME                                                             |
+------------------------------------------------------------------+
| memory/performance_schema/events_statements_history.sqltext      |
| memory/performance_schema/events_statements_current.sqltext      |
| memory/performance_schema/events_statements_history_long.sqltext |
+------------------------------------------------------------------+

mysql> SELECT NAME FROM setup_instruments
       WHERE NAME LIKE 'memory/performance_schema/%.tokens';
+----------------------------------------------------------------------+
| NAME                                                                 |
+----------------------------------------------------------------------+
| memory/performance_schema/events_statements_history.tokens           |
| memory/performance_schema/events_statements_current.tokens           |
| memory/performance_schema/events_statements_summary_by_digest.tokens |
| memory/performance_schema/events_statements_history_long.tokens      |
+----------------------------------------------------------------------+

24.9 Performance Schema General Table Characteristics

The name of the performance_schema database is lowercase, as are the names of tables within it. Queries should specify the names in lowercase.

Many tables in the performance_schema database are read only and cannot be modified:

mysql> TRUNCATE TABLE setup_instruments;
ERROR 1683 (HY000): Invalid performance_schema usage.

Some of the setup tables have columns that can be modified to affect Performance Schema operation; some also permit rows to be inserted or deleted. Truncation is permitted to clear collected events, so TRUNCATE TABLE can be used on tables containing those kinds of information, such as tables named with a prefix of events_waits_.

Summary tables can be truncated with TRUNCATE TABLE. Generally, the effect is to reset the summary columns to 0 or NULL, not to remove rows. This enables you to clear collected values and restart aggregation. That might be useful, for example, after you have made a runtime configuration change. Exceptions to this truncation behavior are noted in individual summary table sections.

Privileges are as for other databases and tables:

  • To retrieve from performance_schema tables, you must have the SELECT privilege.

  • To change those columns that can be modified, you must have the UPDATE privilege.

  • To truncate tables that can be truncated, you must have the DROP privilege.

Because only a limited set of privileges apply to Performance Schema tables, attempts to use GRANT ALL as shorthand for granting privileges at the database or table leval fail with an error:

mysql> GRANT ALL ON performance_schema.*
       TO 'u1'@'localhost';
ERROR 1044 (42000): Access denied for user 'root'@'localhost'
to database 'performance_schema'
mysql> GRANT ALL ON performance_schema.setup_instruments
       TO 'u2'@'localhost';
ERROR 1044 (42000): Access denied for user 'root'@'localhost'
to database 'performance_schema'

Instead, grant exactly the desired privileges:

mysql> GRANT SELECT ON performance_schema.*
       TO 'u1'@'localhost';
Query OK, 0 rows affected (0.03 sec)

mysql> GRANT SELECT, UPDATE ON performance_schema.setup_instruments
       TO 'u2'@'localhost';
Query OK, 0 rows affected (0.02 sec)

24.10 Performance Schema Table Descriptions

Tables in the performance_schema database can be grouped as follows:

  • Setup tables. These tables are used to configure and display monitoring characteristics.

  • Current events tables. The events_waits_current table contains the most recent event for each thread. Other similar tables contain current events at different levels of the event hierarchy: events_stages_current for stage events, events_statements_current for statement events, and events_transactions_current for transaction events.

  • History tables. These tables have the same structure as the current events tables, but contain more rows. For example, for wait events, events_waits_history table contains the most recent 10 events per thread. events_waits_history_long contains the most recent 10,000 events. Other similar tables exist for stage, statement, and transaction histories.

    To change the sizes of the history tables, set the appropriate system variables at server startup. For example, to set the sizes of the wait event history tables, set performance_schema_events_waits_history_size and performance_schema_events_waits_history_long_size.

  • Summary tables. These tables contain information aggregated over groups of events, including those that have been discarded from the history tables.

  • Instance tables. These tables document what types of objects are instrumented. An instrumented object, when used by the server, produces an event. These tables provide event names and explanatory notes or status information.

  • Miscellaneous tables. These do not fall into any of the other table groups.

24.10.1 Performance Schema Table Index

The following table lists each Performance Schema table and provides a short description of each one.

Table 24.1 Performance Schema Tables

Table NameDescription
accountsConnection statistics per client account
cond_instancessynchronization object instances
events_stages_currentCurrent stage events
events_stages_historyMost recent stage events for each thread
events_stages_history_longMost recent stage events overall
events_stages_summary_by_account_by_event_nameStage events per account and event name
events_stages_summary_by_host_by_event_nameStage events per host name and event name
events_stages_summary_by_thread_by_event_nameStage waits per thread and event name
events_stages_summary_by_user_by_event_nameStage events per user name and event name
events_stages_summary_global_by_event_nameStage waits per event name
events_statements_currentCurrent statement events
events_statements_historyMost recent statement events for each thread
events_statements_history_longMost recent statement events overall
events_statements_summary_by_account_by_event_nameStatement events per account and event name
events_statements_summary_by_digestStatement events per schema and digest value
events_statements_summary_by_host_by_event_nameStatement events per host name and event name
events_statements_summary_by_programStatement events per stored program
events_statements_summary_by_thread_by_event_nameStatement events per thread and event name
events_statements_summary_by_user_by_event_nameStatement events per user name and event name
events_statements_summary_global_by_event_nameStatement events per event name
events_transactions_currentCurrent transaction events
events_transactions_historyMost recent transaction events for each thread
events_transactions_history_longMost recent transaction events overall
events_transactions_summary_by_account_by_event_nameTransaction events per account and event name
events_transactions_summary_by_host_by_event_nameTransaction events per host name and event name
events_transactions_summary_by_thread_by_event_nameTransaction events per thread and event name
events_transactions_summary_by_user_by_event_nameTransaction events per user name and event name
events_transactions_summary_global_by_event_nameTransaction events per event name
events_waits_currentCurrent wait events
events_waits_historyMost recent wait events for each thread
events_waits_history_longMost recent wait events overall
events_waits_summary_by_account_by_event_nameWait events per account and event name
events_waits_summary_by_host_by_event_nameWait events per host name and event name
events_waits_summary_by_instanceWait events per instance
events_waits_summary_by_thread_by_event_nameWait events per thread and event name
events_waits_summary_by_user_by_event_nameWait events per user name and event name
events_waits_summary_global_by_event_nameWait events per event name
file_instancesFile instances
file_summary_by_event_nameFile events per event name
file_summary_by_instanceFile events per file instance
global_statusGlobal status variables
global_variablesGlobal system variables
host_cacheInformation from the internal host cache
hostsConnection statistics per client host name
memory_summary_by_account_by_event_nameMemory operations per account and event name
memory_summary_by_host_by_event_nameMemory operations per host and event name
memory_summary_by_thread_by_event_nameMemory operations per thread and event name
memory_summary_by_user_by_event_nameMemory operations per user and event name
memory_summary_global_by_event_nameMemory operations globally per event name
metadata_locksMetadata locks and lock requests
mutex_instancesMutex synchronization object instances
objects_summary_global_by_typeObject summaries
performance_timersWhich event timers are available
prepared_statements_instancesPrepared statement instances and statistics
replication_applier_configurationConfiguration parameters for the transaction applier on the slave
replication_applier_statusCurrent status of the transaction applier on the slave
replication_applier_status_by_coordinatorSQL or coordinator thread applier status
replication_applier_status_by_workerWorker thread applier status (empty unless slave is multi-threaded)
replication_connection_configurationConfiguration parameters for connecting to the master
replication_connection_statusCurrent status of the connection to the master
rwlock_instancesLock synchronization object instances
session_account_connect_attrsConnection attributes per for the current session
session_connect_attrsConnection attributes for all sessions
session_statusStatus variables for current session
session_variablesSystem variables for current session
setup_actorsHow to initialize monitoring for new foreground threads
setup_consumersConsumers for which event information can be stored
setup_instrumentsClasses of instrumented objects for which events can be collected
setup_objectsWhich objects should be monitored
setup_timersCurrent event timer
socket_instancesActive connection instances
socket_summary_by_event_nameSocket waits and I/O per event name
socket_summary_by_instanceSocket waits and I/O per instance
status_by_accountSession status variables per account
status_by_hostSession status variables per host name
status_by_threadSession status variables per session
status_by_userSession status variables per user name
table_handlesTable locks and lock requests
table_io_waits_summary_by_index_usageTable I/O waits per index
table_io_waits_summary_by_tableTable I/O waits per table
table_lock_waits_summary_by_tableTable lock waits per table
threadsInformation about server threads
user_variables_by_threadUser-defined variables per thread
usersConnection statistics per client user name
variables_by_threadSession system variables per session

24.10.2 Performance Schema Setup Tables

The setup tables provide information about the current instrumentation and enable the monitoring configuration to be changed. For this reason, some columns in these tables can be changed if you have the UPDATE privilege.

The use of tables rather than individual variables for setup information provides a high degree of flexibility in modifying Performance Schema configuration. For example, you can use a single statement with standard SQL syntax to make multiple simultaneous configuration changes.

These setup tables are available:

24.10.2.1 The setup_actors Table

The setup_actors table contains information that determines whether to enable monitoring and historical event logging for new foreground server threads (threads associated with client connections). This table has a maximum size of 100 rows by default. To change the table size, modify the performance_schema_setup_actors_size system variable at server startup.

For each new foreground thread, the Performance Schema matches the user and host for the thread against the rows of the setup_actors table. If a row from that table matches, its ENABLED and HISTORY column values are used to set the the INSTRUMENTED and HISTORY columns, respectively, of the threads table row for the thread. This enables instrumenting and historical event logging to be applied selectively per host, user, or account (user and host combination). If there is no match, the INSTRUMENTED and HISTORY columns for the thread are set to NO.

For background threads, there is no associated user. INSTRUMENTED and HISTORY are YES by default and setup_actors is not consulted.

The initial contents of the setup_actors table match any user and host combination, so monitoring and historical event collection are enabled by default for all foreground threads:

mysql> SELECT * FROM setup_actors;
+------+------+------+---------+---------+
| HOST | USER | ROLE | ENABLED | HISTORY |
+------+------+------+---------+---------+
| %    | %    | %    | YES     | YES     |
+------+------+------+---------+---------+

For information about how to use the setup_actors table to affect event monitoring, see Section 24.3.6, “Pre-Filtering by Thread”.

Modifications to the setup_actors table affect only foreground threads created subsequent to the modification, not existing threads. To affect existing threads, modify the INSTRUMENTED and HISTORY columns of threads table rows.

The setup_actors table has these columns:

  • HOST

    The host name. This should be a literal name, or '%' to mean any host.

  • USER

    The user name. This should be a literal name, or '%' to mean any user.

  • ROLE

    Unused.

  • ENABLED

    Whether to enable instrumentation for foreground threads matched by the row. The value is YES or NO.

    This column was added in MySQL 5.7.6. For earlier versions in which it is not present, the Performance Schema enables instrumentation only for foreground threads matched by some row in the table; instrumentation is implicitly disabled for nonmatching threads.

  • HISTORY

    Whether to log historical events for foreground threads matched by the row. The value is YES or NO.

    This column was added in MySQL 5.7.8. For earlier versions in which it is not present, the Performance Schema logs historical events either for all threads or no threads, depending on which history consumers are enabled or disabled.

TRUNCATE TABLE is permitted for the setup_actors table. It removes the rows.

24.10.2.2 The setup_consumers Table

The setup_consumers table lists the types of consumers for which event information can be stored and which are enabled:

mysql> SELECT * FROM setup_consumers;
+----------------------------------+---------+
| NAME                             | ENABLED |
+----------------------------------+---------+
| events_stages_current            | NO      |
| events_stages_history            | NO      |
| events_stages_history_long       | NO      |
| events_statements_current        | YES     |
| events_statements_history        | YES     |
| events_statements_history_long   | NO      |
| events_transactions_current      | NO      |
| events_transactions_history      | NO      |
| events_transactions_history_long | NO      |
| events_waits_current             | NO      |
| events_waits_history             | NO      |
| events_waits_history_long        | NO      |
| global_instrumentation           | YES     |
| thread_instrumentation           | YES     |
| statements_digest                | YES     |
+----------------------------------+---------+

The consumer settings in the setup_consumers table form a hierarchy from higher levels to lower. For detailed information about the effect of enabling different consumers, see Section 24.3.7, “Pre-Filtering by Consumer”.

Modifications to the setup_consumers table affect monitoring immediately.

The setup_consumers table has these columns:

  • NAME

    The consumer name.

  • ENABLED

    Whether the consumer is enabled. The value is YES or NO. This column can be modified. If you disable a consumer, the server does not spend time adding event information to it.

TRUNCATE TABLE is not permitted for the setup_consumers table.

24.10.2.3 The setup_instruments Table

The setup_instruments table lists classes of instrumented objects for which events can be collected:

mysql> SELECT * FROM setup_instruments;
+------------------------------------------------------------+---------+-------+
| NAME                                                       | ENABLED | TIMED |
+------------------------------------------------------------+---------+-------+
...
| wait/synch/mutex/sql/LOCK_global_read_lock                 | YES     | YES   |
| wait/synch/mutex/sql/LOCK_global_system_variables          | YES     | YES   |
| wait/synch/mutex/sql/LOCK_lock_db                          | YES     | YES   |
| wait/synch/mutex/sql/LOCK_manager                          | YES     | YES   |
...
| wait/synch/rwlock/sql/LOCK_grant                           | YES     | YES   |
| wait/synch/rwlock/sql/LOGGER::LOCK_logger                  | YES     | YES   |
| wait/synch/rwlock/sql/LOCK_sys_init_connect                | YES     | YES   |
| wait/synch/rwlock/sql/LOCK_sys_init_slave                  | YES     | YES   |
...
| wait/io/file/sql/binlog                                    | YES     | YES   |
| wait/io/file/sql/binlog_index                              | YES     | YES   |
| wait/io/file/sql/casetest                                  | YES     | YES   |
| wait/io/file/sql/dbopt                                     | YES     | YES   |
...

Each instrument added to the source code provides a row for this table, even when the instrumented code is not executed. When an instrument is enabled and executed, instrumented instances are created, which are visible in the *_instances tables.

Modifications to most setup_instruments rows affect monitoring immediately. For some instruments, modifications are effective only at server startup; changing them at runtime has no effect. This affects primarily mutexes, conditions, and rwlocks in the server, although there may be other instruments for which this is true.

For more information about the role of the setup_instruments table in event filtering, see Section 24.3.3, “Event Pre-Filtering”.

The setup_instruments table has these columns:

  • NAME

    The instrument name. Instrument names may have multiple parts and form a hierarchy, as discussed in Section 24.5, “Performance Schema Instrument Naming Conventions”. Events produced from execution of an instrument have an EVENT_NAME value that is taken from the instrument NAME value. (Events do not really have a name, but this provides a way to associate events with instruments.)

  • ENABLED

    Whether the instrument is enabled. The value is YES or NO. This column can be modified. A disabled instrument produces no events.

  • TIMED

    Whether the instrument is timed. This column can be modified.

    For memory instruments, the TIMED column in setup_instruments is ignored because memory operations are not timed.

    If an enabled instrument is not timed, the instrument code is enabled, but the timer is not. Events produced by the instrument have NULL for the TIMER_START, TIMER_END, and TIMER_WAIT timer values. This in turn causes those values to be ignored when calculating the sum, minimum, maximum, and average time values in summary tables.

TRUNCATE TABLE is not permitted for the setup_instruments table.

24.10.2.4 The setup_objects Table

The setup_objects table controls whether the Performance Schema monitors particular objects. This table has a maximum size of 100 rows by default. To change the table size, modify the performance_schema_setup_objects_size system variable at server startup.

The initial setup_objects contents look like this:

mysql> SELECT * FROM setup_objects;
+-------------+--------------------+-------------+---------+-------+
| OBJECT_TYPE | OBJECT_SCHEMA      | OBJECT_NAME | ENABLED | TIMED |
+-------------+--------------------+-------------+---------+-------+
| EVENT       | mysql              | %           | NO      | NO    |
| EVENT       | performance_schema | %           | NO      | NO    |
| EVENT       | information_schema | %           | NO      | NO    |
| EVENT       | %                  | %           | YES     | YES   |
| FUNCTION    | mysql              | %           | NO      | NO    |
| FUNCTION    | performance_schema | %           | NO      | NO    |
| FUNCTION    | information_schema | %           | NO      | NO    |
| FUNCTION    | %                  | %           | YES     | YES   |
| PROCEDURE   | mysql              | %           | NO      | NO    |
| PROCEDURE   | performance_schema | %           | NO      | NO    |
| PROCEDURE   | information_schema | %           | NO      | NO    |
| PROCEDURE   | %                  | %           | YES     | YES   |
| TABLE       | mysql              | %           | NO      | NO    |
| TABLE       | performance_schema | %           | NO      | NO    |
| TABLE       | information_schema | %           | NO      | NO    |
| TABLE       | %                  | %           | YES     | YES   |
| TRIGGER     | mysql              | %           | NO      | NO    |
| TRIGGER     | performance_schema | %           | NO      | NO    |
| TRIGGER     | information_schema | %           | NO      | NO    |
| TRIGGER     | %                  | %           | YES     | YES   |
+-------------+--------------------+-------------+---------+-------+

Modifications to the setup_objects table affect object monitoring immediately.

For object types listed in setup_objects, the Performance Schema uses the table to how to monitor them. Object matching is based on the OBJECT_SCHEMA and OBJECT_NAME columns. Objects for which there is no match are not monitored.

The effect of the default object configuration is to instrument all tables except those in the mysql, INFORMATION_SCHEMA, and performance_schema databases. (Tables in the INFORMATION_SCHEMA database are not instrumented regardless of the contents of setup_objects; the row for information_schema.% simply makes this default explicit.)

When the Performance Schema checks for a match in setup_objects, it tries to find more specific matches first. For example, with a table db1.t1, it looks for a match for 'db1' and 't1', then for 'db1' and '%', then for '%' and '%'. The order in which matching occurs matters because different matching setup_objects rows can have different ENABLED and TIMED values.

Rows can be inserted into or deleted from setup_objects by users with the INSERT or DELETE privilege on the table. For existing rows, only the ENABLED and TIMED columns can be modified, by users with the UPDATE privilege on the table.

For more information about the role of the setup_objects table in event filtering, see Section 24.3.3, “Event Pre-Filtering”.

The setup_objects table has these columns:

  • OBJECT_TYPE

    The type of object to instrument. The value is one of 'EVENT' (Event Scheduler event), 'FUNCTION' (stored function), 'PROCEDURE' (stored procedure), 'TABLE' (base table), or 'TRIGGER' (trigger). Before MySQL 5.7.2, the value is always 'TABLE'.

    TABLE filtering affects table I/O events (wait/io/table/sql/handler instrument) and table lock events (wait/lock/table/sql/handler instrument).

  • OBJECT_SCHEMA

    The schema that contains the object. This should be a literal name, or '%' to mean any schema.

  • OBJECT_NAME

    The name of the instrumented object. This should be a literal name, or '%' to mean any object.

  • ENABLED

    Whether events for the object are instrumented. The value is YES or NO. This column can be modified.

  • TIMED

    Whether events for the object are timed. This column can be modified.

TRUNCATE TABLE is permitted for the setup_objects table. It removes the rows.

24.10.2.5 The setup_timers Table

The setup_timers table shows the currently selected event timers:

mysql> SELECT * FROM setup_timers;
+-------------+-------------+
| NAME        | TIMER_NAME  |
+-------------+-------------+
| idle        | MICROSECOND |
| wait        | CYCLE       |
| stage       | NANOSECOND  |
| statement   | NANOSECOND  |
| transaction | NANOSECOND  |
+-------------+-------------+

The setup_timers.TIMER_NAME value can be changed to select a different timer. The value can be any of the values in the performance_timers.TIMER_NAME column. For an explanation of how event timing occurs, see Section 24.3.1, “Performance Schema Event Timing”.

Modifications to the setup_timers table affect monitoring immediately. Events already in progress may use the original timer for the begin time and the new timer for the end time. To avoid unpredictable results after you make timer changes, use TRUNCATE TABLE to reset Performance Schema statistics.

The setup_timers table has these columns:

  • NAME

    The type of instrument the timer is used for.

  • TIMER_NAME

    The timer that applies to the instrument type. This column can be modified.

TRUNCATE TABLE is not permitted for the setup_timers table.

24.10.3 Performance Schema Instance Tables

Instance tables document what types of objects are instrumented. They provide event names and explanatory notes or status information:

These tables list instrumented synchronization objects, files, and connections. There are three types of synchronization objects: cond, mutex, and rwlock. Each instance table has an EVENT_NAME or NAME column to indicate the instrument associated with each row. Instrument names may have multiple parts and form a hierarchy, as discussed in Section 24.5, “Performance Schema Instrument Naming Conventions”.

The mutex_instances.LOCKED_BY_THREAD_ID and rwlock_instances.WRITE_LOCKED_BY_THREAD_ID columns are extremely important for investigating performance bottlenecks or deadlocks. For examples of how to use them for this purpose, see Section 24.17, “Using the Performance Schema to Diagnose Problems”

24.10.3.1 The cond_instances Table

The cond_instances table lists all the conditions seen by the Performance Schema while the server executes. A condition is a synchronization mechanism used in the code to signal that a specific event has happened, so that a thread waiting for this condition can resume work.

When a thread is waiting for something to happen, the condition name is an indication of what the thread is waiting for, but there is no immediate way to tell which other thread, or threads, will cause the condition to happen.

The cond_instances table has these columns:

  • NAME

    The instrument name associated with the condition.

  • OBJECT_INSTANCE_BEGIN

    The address in memory of the instrumented condition.

TRUNCATE TABLE is not permitted for the cond_instances table.

24.10.3.2 The file_instances Table

The file_instances table lists all the files seen by the Performance Schema when executing file I/O instrumentation. If a file on disk has never been opened, it will not be in file_instances. When a file is deleted from the disk, it is also removed from the file_instances table.

The file_instances table has these columns:

  • FILE_NAME

    The file name.

  • EVENT_NAME

    The instrument name associated with the file.

  • OPEN_COUNT

    The count of open handles on the file. If a file was opened and then closed, it was opened 1 time, but OPEN_COUNT will be 0. To list all the files currently opened by the server, use WHERE OPEN_COUNT > 0.

TRUNCATE TABLE is not permitted for the file_instances table.

24.10.3.3 The mutex_instances Table

The mutex_instances table lists all the mutexes seen by the Performance Schema while the server executes. A mutex is a synchronization mechanism used in the code to enforce that only one thread at a given time can have access to some common resource. The resource is said to be protected by the mutex.

When two threads executing in the server (for example, two user sessions executing a query simultaneously) do need to access the same resource (a file, a buffer, or some piece of data), these two threads will compete against each other, so that the first query to obtain a lock on the mutex will cause the other query to wait until the first is done and unlocks the mutex.

The work performed while holding a mutex is said to be in a critical section, and multiple queries do execute this critical section in a serialized way (one at a time), which is a potential bottleneck.

The mutex_instances table has these columns:

  • NAME

    The instrument name associated with the mutex.

  • OBJECT_INSTANCE_BEGIN

    The address in memory of the instrumented mutex.

  • LOCKED_BY_THREAD_ID

    When a thread currently has a mutex locked, LOCKED_BY_THREAD_ID is the THREAD_ID of the locking thread, otherwise it is NULL.

TRUNCATE TABLE is not permitted for the mutex_instances table.

For every mutex instrumented in the code, the Performance Schema provides the following information.

  • The setup_instruments table lists the name of the instrumentation point, with the prefix wait/synch/mutex/.

  • When some code creates a mutex, a row is added to the mutex_instances table. The OBJECT_INSTANCE_BEGIN column is a property that uniquely identifies the mutex.

  • When a thread attempts to lock a mutex, the events_waits_current table shows a row for that thread, indicating that it is waiting on a mutex (in the EVENT_NAME column), and indicating which mutex is waited on (in the OBJECT_INSTANCE_BEGIN column).

  • When a thread succeeds in locking a mutex:

  • When a thread unlocks a mutex, mutex_instances shows that the mutex now has no owner (the THREAD_ID column is NULL).

  • When a mutex object is destroyed, the corresponding row is removed from mutex_instances.

By performing queries on both of the following tables, a monitoring application or a DBA can detect bottlenecks or deadlocks between threads that involve mutexes:

24.10.3.4 The rwlock_instances Table

The rwlock_instances table lists all the rwlock (read write lock) instances seen by the Performance Schema while the server executes. An rwlock is a synchronization mechanism used in the code to enforce that threads at a given time can have access to some common resource following certain rules. The resource is said to be protected by the rwlock. The access is either shared (many threads can have a read lock at the same time), exclusive (only one thread can have a write lock at a given time), or shared-exclusive (a thread can have a write lock while permitting inconsistent reads by other threads). Shared-exclusive access is otherwise known as an sxlock and was introduced in MySQL 5.7 to optimize concurrency and improve scalability for read-write workloads.

Depending on how many threads are requesting a lock, and the nature of the locks requested, access can be either granted in shared mode, exclusive mode, shared-exclusive mode or not granted at all, waiting for other threads to finish first.

The rwlock_instances table has these columns:

  • NAME

    The instrument name associated with the lock.

  • OBJECT_INSTANCE_BEGIN

    The address in memory of the instrumented lock.

  • WRITE_LOCKED_BY_THREAD_ID

    When a thread currently has an rwlock locked in exclusive (write) mode, WRITE_LOCKED_BY_THREAD_ID is the THREAD_ID of the locking thread, otherwise it is NULL.

  • READ_LOCKED_BY_COUNT

    When a thread currently has an rwlock locked in shared (read) mode, READ_LOCKED_BY_COUNT is incremented by 1. This is a counter only, so it cannot be used directly to find which thread holds a read lock, but it can be used to see whether there is a read contention on an rwlock, and see how many readers are currently active.

TRUNCATE TABLE is not permitted for the rwlock_instances table.

By performing queries on both of the following tables, a monitoring application or a DBA may detect some bottlenecks or deadlocks between threads that involve locks:

There is a limitation: The rwlock_instances can be used only to identify the thread holding a write lock, but not the threads holding a read lock.

24.10.3.5 The socket_instances Table

The socket_instances table provides a real-time snapshot of the active connections to the MySQL server. The table contains one row per TCP/IP or Unix socket file connection. Information available in this table provides a real-time snapshot of the active connections to the server. (Additional information is available in socket summary tables, including network activity such as socket operations and number of bytes transmitted and received; see Section 24.10.15.8, “Socket Summary Tables”).

mysql> SELECT * FROM socket_instances\G
*************************** 1. row ***************************
           EVENT_NAME: wait/io/socket/sql/server_unix_socket
OBJECT_INSTANCE_BEGIN: 4316619408
            THREAD_ID: 1
            SOCKET_ID: 16
                   IP:
                 PORT: 0
                STATE: ACTIVE
*************************** 2. row ***************************
           EVENT_NAME: wait/io/socket/sql/client_connection
OBJECT_INSTANCE_BEGIN: 4316644608
            THREAD_ID: 21
            SOCKET_ID: 39
                   IP: 127.0.0.1
                 PORT: 55233
                STATE: ACTIVE
*************************** 3. row ***************************
           EVENT_NAME: wait/io/socket/sql/server_tcpip_socket
OBJECT_INSTANCE_BEGIN: 4316699040
            THREAD_ID: 1
            SOCKET_ID: 14
                   IP: 0.0.0.0
                 PORT: 50603
                STATE: ACTIVE

Socket instruments have names of the form wait/io/socket/sql/socket_type and are used like this:

  1. The server has a listening socket for each network protocol that it supports. The instruments associated with listening sockets for TCP/IP or Unix socket file connections have a socket_type value of server_tcpip_socket or server_unix_socket, respectively.

  2. When a listening socket detects a connection, the server transfers the connection to a new socket managed by a separate thread. The instrument for the new connection thread has a socket_type value of client_connection.

  3. When a connection terminates, the row in socket_instances corresponding to it is deleted.

The socket_instances table has these columns:

  • EVENT_NAME

    The name of the wait/io/socket/* instrument that produced the event. This is a NAME value from the setup_instruments table. Instrument names may have multiple parts and form a hierarchy, as discussed in Section 24.5, “Performance Schema Instrument Naming Conventions”.

  • OBJECT_INSTANCE_BEGIN

    This column uniquely identifies the socket. The value is the address of an object in memory.

  • THREAD_ID

    The internal thread identifier assigned by the server. Each socket is managed by a single thread, so each socket can be mapped to a thread which can be mapped to a server process.

  • SOCKET_ID

    The internal file handle assigned to the socket.

  • IP

    The client IP address. The value may be either an IPv4 or IPv6 address, or blank to indicate a Unix socket file connection.

  • PORT

    The TCP/IP port number, in the range from 0 to 65535.

  • STATE

    The socket status, either IDLE or ACTIVE. Wait times for active sockets are tracked using the corresponding socket instrument. Wait times for idle sockets are tracked using the idle instrument.

    A socket is idle if it is waiting for a request from the client. When a socket becomes idle, the event row in socket_instances that is tracking the socket switches from a status of ACTIVE to IDLE. The EVENT_NAME value remains wait/io/socket/*, but timing for the instrument is suspended. Instead, an event is generated in the events_waits_current table with an EVENT_NAME value of idle.

    When the next request is received, the idle event terminates, the socket instance switches from IDLE to ACTIVE, and timing of the socket instrument resumes.

TRUNCATE TABLE is not permitted for the socket_instances table.

The IP:PORT column combination value identifies the connection. This combination value is used in the OBJECT_NAME column of the events_waits_xxx tables, to identify the connection from which socket events come:

  • For the Unix domain listener socket (server_unix_socket), the port is 0, and the IP is ''.

  • For client connections via the Unix domain listener (client_connection), the port is 0, and the IP is ''.

  • For the TCP/IP server listener socket (server_tcpip_socket), the port is always the master port (for example, 3306), and the IP is always 0.0.0.0.

  • For client connections via the TCP/IP listener (client_connection), the port is whatever the server assigns, but never 0. The IP is the IP of the originating host (127.0.0.1 or ::1 for the local host)

24.10.4 Performance Schema Wait Event Tables

These tables store wait events:

The following sections describe those tables. There are also summary tables that aggregate information about wait events; see Section 24.10.15.1, “Wait Event Summary Tables”.

Wait Event Configuration

To enable collection of wait events, enable the relevant instruments and consumers.

The setup_instruments table contains instruments with names that begin with wait. For example:

mysql> SELECT * FROM setup_instruments
       WHERE NAME LIKE 'wait/io/file/innodb%';
+--------------------------------------+---------+-------+
| NAME                                 | ENABLED | TIMED |
+--------------------------------------+---------+-------+
| wait/io/file/innodb/innodb_data_file | YES     | YES   |
| wait/io/file/innodb/innodb_log_file  | YES     | YES   |
| wait/io/file/innodb/innodb_temp_file | YES     | YES   |
+--------------------------------------+---------+-------+
mysql> SELECT * FROM setup_instruments WHERE
       NAME LIKE 'wait/io/socket/%';
+----------------------------------------+---------+-------+
| NAME                                   | ENABLED | TIMED |
+----------------------------------------+---------+-------+
| wait/io/socket/sql/server_tcpip_socket | NO      | NO    |
| wait/io/socket/sql/server_unix_socket  | NO      | NO    |
| wait/io/socket/sql/client_connection   | NO      | NO    |
+----------------------------------------+---------+-------+

To modify collection of wait events, change the ENABLED and TIMING columns of the relevant instruments. For example:

mysql> UPDATE setup_instruments SET ENABLED = 'YES', TIMED = 'YES'
       WHERE NAME LIKE 'wait/io/socket/sql/%';

The setup_consumers table contains consumer values with names corresponding to the current and recent wait event table names. These consumers may be used to filter collection of wait events. The wait consumers are disabled by default:

mysql> SELECT * FROM setup_consumers WHERE NAME LIKE '%waits%';
+---------------------------+---------+
| NAME                      | ENABLED |
+---------------------------+---------+
| events_waits_current      | NO      |
| events_waits_history      | NO      |
| events_waits_history_long | NO      |
+---------------------------+---------+

To enable all wait consumers, do this:

mysql> UPDATE setup_consumers SET ENABLED = 'YES'
       WHERE NAME LIKE '%waits%';

The setup_timers table contains a row with a NAME value of wait that indicates the unit for wait event timing. The default unit is CYCLE.

mysql> SELECT * FROM setup_timers WHERE NAME = 'wait';
+------+------------+
| NAME | TIMER_NAME |
+------+------------+
| wait | CYCLE      |
+------+------------+

To change the timing unit, modify the TIMER_NAME value:

mysql> UPDATE setup_timers SET TIMER_NAME = 'NANOSECOND'
       WHERE NAME = 'wait';

For additional information about configuring event collection, see Section 24.3, “Performance Schema Runtime Configuration”.

24.10.4.1 The events_waits_current Table

The events_waits_current table contains current wait events, one row per thread showing the current status of the thread's most recent monitored wait event.

Of the tables that contain wait event rows, events_waits_current is the most fundamental. Other tables that contain wait event rows are logically derived from the current events. For example, the events_waits_history and events_waits_history_long tables are collections of the most recent wait events, up to a fixed number of rows.

For information about configuration of wait event collection, see Section 24.10.4, “Performance Schema Wait Event Tables”.

The events_waits_current table has these columns:

  • THREAD_ID, EVENT_ID

    The thread associated with the event and the thread current event number when the event starts. The THREAD_ID and EVENT_ID values taken together uniquely identify the row. No two rows have the same pair of values.

  • END_EVENT_ID

    This column is set to NULL when the event starts and updated to the thread current event number when the event ends.

  • EVENT_NAME

    The name of the instrument that produced the event. This is a NAME value from the setup_instruments table. Instrument names may have multiple parts and form a hierarchy, as discussed in Section 24.5, “Performance Schema Instrument Naming Conventions”.

  • SOURCE

    The name of the source file containing the instrumented code that produced the event and the line number in the file at which the instrumentation occurs. This enables you to check the source to determine exactly what code is involved. For example, if a mutex or lock is being blocked, you can check the context in which this occurs.

  • TIMER_START, TIMER_END, TIMER_WAIT

    Timing information for the event. The unit for these values is picoseconds (trillionths of a second). The TIMER_START and TIMER_END values indicate when event timing started and ended. TIMER_WAIT is the event elapsed time (duration).

    If an event has not finished, TIMER_END and TIMER_WAIT are NULL before MySQL 5.7.8. As of 5.7.8, TIMER_END is the current timer value and TIMER_WAIT is the time elapsed so far (TIMER_ENDTIMER_START).

    If an event is produced from an instrument that has TIMED = NO, timing information is not collected, and TIMER_START, TIMER_END, and TIMER_WAIT are all NULL.

    For discussion of picoseconds as the unit for event times and factors that affect time values, see Section 24.3.1, “Performance Schema Event Timing”.

  • SPINS

    For a mutex, the number of spin rounds. If the value is NULL, the code does not use spin rounds or spinning is not instrumented.

  • OBJECT_SCHEMA, OBJECT_NAME, OBJECT_TYPE, OBJECT_INSTANCE_BEGIN

    These columns identify the object being acted on. What that means depends on the object type.

    For a synchronization object (cond, mutex, rwlock):

    • OBJECT_SCHEMA, OBJECT_NAME, and OBJECT_TYPE are NULL.

    • OBJECT_INSTANCE_BEGIN is the address of the synchronization object in memory.

    For a file I/O object:

    • OBJECT_SCHEMA is NULL.

    • OBJECT_NAME is the file name.

    • OBJECT_TYPE is FILE.

    • OBJECT_INSTANCE_BEGIN is an address in memory.

    For a socket object:

    • OBJECT_NAME is the IP:PORT value for the socket.

    • OBJECT_INSTANCE_BEGIN is an address in memory.

    For a table I/O object:

    • OBJECT_SCHEMA is the name of the schema that contains the table.

    • OBJECT_NAME is the table name.

    • OBJECT_TYPE is TABLE for a persistent base table or TEMPORARY TABLE for a temporary table.

    • OBJECT_INSTANCE_BEGIN is an address in memory.

    An OBJECT_INSTANCE_BEGIN value itself has no meaning, except that different values indicate different objects. OBJECT_INSTANCE_BEGIN can be used for debugging. For example, it can be used with GROUP BY OBJECT_INSTANCE_BEGIN to see whether the load on 1,000 mutexes (that protect, say, 1,000 pages or blocks of data) is spread evenly or just hitting a few bottlenecks. This can help you correlate with other sources of information if you see the same object address in a log file or another debugging or performance tool.

  • INDEX_NAME

    The name of the index used. PRIMARY indicates the table primary index. NULL means that no index was used.

  • NESTING_EVENT_ID

    The EVENT_ID value of the event within which this event is nested.

  • NESTING_EVENT_TYPE

    The nesting event type. The value is TRANSACTION, STATEMENT, STAGE, or WAIT.

  • OPERATION

    The type of operation performed, such as lock, read, or write.

  • NUMBER_OF_BYTES

    The number of bytes read or written by the operation. For table I/O waits (events for the wait/io/table/sql/handler instrument), NUMBER_OF_BYTES is NULL before MySQL 5.7.5. For table I/O events as of 5.7.5, this column indicates the number of rows. If the value is greater than 1, the event is for a batch I/O operation. The following discussion describes the difference between exclusively single-row reporting and reporting that reflects batch I/O.

    MySQL executes joins using a nested-loop implementation. The job of the Performance Schema instrumentation is to provide row count and accumulated execution time per table in the join. Assume a join query of the following form that is executed using a table join order of t1, t2, t3:

    SELECT ... FROM t1 JOIN t2 ON ... JOIN t3 ON ...
    

    Table fanout is the increase or decrease in number of rows from adding a table during join processing. If the fanout for table t3 is greater than 1, the majority of row-fetch operations are for that table. Suppose that the join accesses 10 rows from t1, 20 rows from t2 per row from t1, and 30 rows from t3 per row of table t2. With single-row reporting, the total number of instrumented operations is:

    10 + (10 * 20) + (10 * 20 * 30) = 6210
    

    A significant reduction in the number of instrumented operations is achievable by aggregating them per scan (that is, per unique combination of rows from t1 and t2). With batch I/O reporting, the Performance Schema produces an event for each scan of the innermost table t3 rather than for each row, and the number of instrumented row operations reduces to:

    10 + (10 * 20) + (10 * 20) = 410
    

    That is a reduction of 93%, illustrating how the batch-reporting strategy significantly reduces Performance Schema overhead for table I/O by reducing the number of reporting calls. The tradeoff is lesser accuracy for event timing. Rather than time for an individual row operation as in per-row reporting, timing for batch I/O includes time spent for operations such as join buffering, aggregation, and returning rows to the client.

    For batch I/O reporting to occur, these conditions must be true:

    • Query execution accesses the innermost table of a query block (for a single-table query, that table counts as innermost)

    • Query execution does not request a single row from the table (so, for example, eq_ref access prevents use of batch reporting)

    • Query execution does not evaluate a subquery containing table access for the table

  • FLAGS

    Reserved for future use.

TRUNCATE TABLE is permitted for the events_waits_current table. It removes the rows.

24.10.4.2 The events_waits_history Table

The events_waits_history table contains the most recent N wait events per thread. The value of N is autosized at server startup. To set the table size explicitly, set the performance_schema_events_waits_history_size system variable at server startup. Wait events are not added to the table until they have ended. As new events are added, older events are discarded if the table is full.

The events_waits_history table has the same structure as events_waits_current. See Section 24.10.4.1, “The events_waits_current Table”.

TRUNCATE TABLE is permitted for the events_waits_history table. It removes the rows.

For information about configuration of wait event collection, see Section 24.10.4, “Performance Schema Wait Event Tables”.

24.10.4.3 The events_waits_history_long Table

The events_waits_history_long table contains the most recent N wait events. The value of N is autosized at server startup. To set the table size explicitly, set the performance_schema_events_waits_history_long_size system variable at server startup. Wait events are not added to the table until they have ended. As new events are added, older events are discarded if the table is full. When a thread ends, its rows are removed from the table.

The events_waits_history_long table has the same structure as events_waits_current. See Section 24.10.4.1, “The events_waits_current Table”.

TRUNCATE TABLE is permitted for the events_waits_history_long table. It removes the rows.

For information about configuration of wait event collection, see Section 24.10.4, “Performance Schema Wait Event Tables”.

24.10.5 Performance Schema Stage Event Tables

The Performance Schema instruments stages, which are steps during the statement-execution process, such as parsing a statement, opening a table, or performing a filesort operation. Stages correspond to the thread states displayed by SHOW PROCESSLIST or that are visible in the INFORMATION_SCHEMA.PROCESSLIST table. Stages begin and end when state values change.

Within the event hierarchy, wait events nest within stage events, which nest within statement events, which nest within transaction events.

These tables store stage events:

The following sections describe those tables. There are also summary tables that aggregate information about stage events; see Section 24.10.15.2, “Stage Summary Tables”.

Stage Event Configuration

To enable collection of stage events, enable the relevant instruments and consumers.

The setup_instruments table contains instruments with names that begin with stage. Other than those instruments that provide statement progress information, these instruments are disabled by default. For example:

mysql> SELECT * FROM setup_instruments WHERE NAME RLIKE 'stage/sql/[a-c]';
+----------------------------------------------------+---------+-------+
| NAME                                               | ENABLED | TIMED |
+----------------------------------------------------+---------+-------+
| stage/sql/After create                             | NO      | NO    |
| stage/sql/allocating local table                   | NO      | NO    |
| stage/sql/altering table                           | NO      | NO    |
| stage/sql/committing alter table to storage engine | NO      | NO    |
| stage/sql/Changing master                          | NO      | NO    |
| stage/sql/Checking master version                  | NO      | NO    |
| stage/sql/checking permissions                     | NO      | NO    |
| stage/sql/checking privileges on cached query      | NO      | NO    |
| stage/sql/checking query cache for query           | NO      | NO    |
| stage/sql/cleaning up                              | NO      | NO    |
| stage/sql/closing tables                           | NO      | NO    |
| stage/sql/Connecting to master                     | NO      | NO    |
| stage/sql/converting HEAP to MyISAM                | NO      | NO    |
| stage/sql/Copying to group table                   | NO      | NO    |
| stage/sql/Copying to tmp table                     | NO      | NO    |
| stage/sql/copy to tmp table                        | NO      | NO    |
| stage/sql/Creating sort index                      | NO      | NO    |
| stage/sql/creating table                           | NO      | NO    |
| stage/sql/Creating tmp table                       | NO      | NO    |
+----------------------------------------------------+---------+-------+

As of MySQL 5.7.7, stage event instruments that provide statement progress information are enabled and timed by default:

mysql> SELECT * FROM setup_instruments WHERE
       ENABLED='YES' AND NAME LIKE "stage/%";
+------------------------------------------------------+---------+-------+
| NAME                                                 | ENABLED | TIMED |
+------------------------------------------------------+---------+-------+
| stage/sql/copy to tmp table                          | YES     | YES   |
| stage/innodb/alter table (end)                       | YES     | YES   |
| stage/innodb/alter table (flush)                     | YES     | YES   |
| stage/innodb/alter table (insert)                    | YES     | YES   |
| stage/innodb/alter table (log apply index)           | YES     | YES   |
| stage/innodb/alter table (log apply table)           | YES     | YES   |
| stage/innodb/alter table (merge sort)                | YES     | YES   |
| stage/innodb/alter table (read PK and internal sort) | YES     | YES   |
| stage/innodb/buffer pool load                        | YES     | YES   |
+------------------------------------------------------+---------+-------+

To modify collection of stage events, change the ENABLED and TIMING columns of the relevant instruments. For example:

mysql> UPDATE setup_instruments SET ENABLED = 'YES', TIMED = 'YES'
       WHERE NAME = 'stage/sql/altering table';

The setup_consumers table contains consumer values with names corresponding to the current and recent stage event table names. These consumers may be used to filter collection of stage events. The stage consumers are disabled by default:

mysql> SELECT * FROM setup_consumers WHERE NAME LIKE '%stages%';
+----------------------------+---------+
| NAME                       | ENABLED |
+----------------------------+---------+
| events_stages_current      | NO      |
| events_stages_history      | NO      |
| events_stages_history_long | NO      |
+----------------------------+---------+

To enable all stage consumers, do this:

mysql> UPDATE setup_consumers SET ENABLED = 'YES'
       WHERE NAME LIKE '%stages%';

The setup_timers table contains a row with a NAME value of stage that indicates the unit for stage event timing. The default unit is NANOSECOND.

mysql> SELECT * FROM setup_timers WHERE NAME = 'stage';
+-------+------------+
| NAME  | TIMER_NAME |
+-------+------------+
| stage | NANOSECOND |
+-------+------------+

To change the timing unit, modify the TIMER_NAME value:

mysql> UPDATE setup_timers SET TIMER_NAME = 'MICROSECOND'
       WHERE NAME = 'stage';

For additional information about configuring event collection, see Section 24.3, “Performance Schema Runtime Configuration”.

Stage Event Progress Information

As of MySQL 5.7.5, the Performance Schema stage event tables contain two columns that, taken together, provide a stage progress indicator for each row:

  • WORK_COMPLETED: The number of work units completed for the stage

  • WORK_ESTIMATED: The number of work units expected for the stage

Each column is NULL if no progress information is provided for an instrument. Interpretation of the information, if it is available, depends entirely on the instrument implementation. The Performance Schema tables provide a container to store progress data, but make no assumptions about the semantics of the metric itself:

  • A work unit is an integer metric that increases over time during execution, such as the number of bytes, rows, files, or tables processed. The definition of work unit for a particular instrument is left to the instrumentation code providing the data.

  • The WORK_COMPLETED value can increase one or many units at a time, depending on the instrumented code.

  • The WORK_ESTIMATED value can change during the stage, depending on the instrumented code.

Instrumentation for a stage event progress indicator can implement any of the following behaviors:

  • No progress instrumentation

    This is the most typical case, where no progress data is provided. The WORK_COMPLETED and WORK_ESTIMATED columns are both NULL.

  • Unbounded progress instrumentation

    Only the WORK_COMPLETED column is meaningful. No data is provided for the WORK_ESTIMATED column, which displays 0.

    By querying the events_stages_current table for the monitored session, a monitoring application can report how much work has been performed so far, but cannot report whether the stage is near completion. Currently, no stages are instrumented like this.

  • Bounded progress instrumentation

    The WORK_COMPLETED and WORK_ESTIMATED columns are both meaningful.

    This type of progress indicator is appropriate for an an operation with a defined completion criterion, such as the table-copy instrument described later. By querying the events_stages_current table for the monitored session, a monitoring application can report how much work has been performed so far, and can report the overall completion percentage for the stage, by computing the WORK_COMPLETED / WORK_ESTIMATED ratio.

The stage/sql/copy to tmp table instrument illustrates how progress indicators work. During execution of an ALTER TABLE statement, the stage/sql/copy to tmp table stage is used, and this stage can execute potentially for a long time, depending on the size of the data to copy.

The table-copy task has a defined termination (all rows copied), and the stage/sql/copy to tmp table stage is instrumented to provided bounded progress information: The work unit used is number of rows copied, WORK_COMPLETED and WORK_ESTIMATED are both meaningful, and their ratio indicates task percentage complete.

To enable the instrument and the relevant consumers, execute these statements:

mysql> UPDATE setup_instruments SET ENABLED='YES'
       WHERE NAME='stage/sql/copy to tmp table';
mysql> UPDATE setup_consumers SET ENABLED='YES'
       WHERE NAME LIKE 'events_stages_%';

To see the progress of an ongoing ALTER TABLE statement, select from the events_stages_current table.

24.10.5.1 The events_stages_current Table

The events_stages_current table contains current stage events, one row per thread showing the current status of the thread's most recent monitored stage event.

Of the tables that contain stage event rows, events_stages_current is the most fundamental. Other tables that contain stage event rows are logically derived from the current events. For example, the events_stages_history and events_stages_history_long tables are collections of the most recent stage events, up to a fixed number of rows.

For information about configuration of stage event collection, see Section 24.10.5, “Performance Schema Stage Event Tables”.

The events_stages_current table has these columns:

  • THREAD_ID, EVENT_ID

    The thread associated with the event and the thread current event number when the event starts. The THREAD_ID and EVENT_ID values taken together uniquely identify the row. No two rows have the same pair of values.

  • END_EVENT_ID

    This column is set to NULL when the event starts and updated to the thread current event number when the event ends.

  • EVENT_NAME

    The name of the instrument that produced the event. This is a NAME value from the setup_instruments table. Instrument names may have multiple parts and form a hierarchy, as discussed in Section 24.5, “Performance Schema Instrument Naming Conventions”.

  • SOURCE

    The name of the source file containing the instrumented code that produced the event and the line number in the file at which the instrumentation occurs. This enables you to check the source to determine exactly what code is involved.

  • TIMER_START, TIMER_END, TIMER_WAIT

    Timing information for the event. The unit for these values is picoseconds (trillionths of a second). The TIMER_START and TIMER_END values indicate when event timing started and ended. TIMER_WAIT is the event elapsed time (duration).

    If an event has not finished, TIMER_END and TIMER_WAIT are NULL before MySQL 5.7.8. As of 5.7.8, TIMER_END is the current timer value and TIMER_WAIT is the time elapsed so far (TIMER_ENDTIMER_START).

    If an event is produced from an instrument that has TIMED = NO, timing information is not collected, and TIMER_START, TIMER_END, and TIMER_WAIT are all NULL.

    For discussion of picoseconds as the unit for event times and factors that affect time values, see Section 24.3.1, “Performance Schema Event Timing”.

  • WORK_COMPLETED, WORK_ESTIMATED

    These columns provide stage progress information, for instruments that have been implemented to produce such information. WORK_COMPLETED indicates how many work units have been completed for the stage, and WORK_ESTIMATED indicates how many work units are expected for the stage. For more information, see Stage Event Progress Information.

    These columns were added in MySQL 5.7.5.

  • NESTING_EVENT_ID

    The EVENT_ID value of the event within which this event is nested. The nesting event for a stage event is usually a statement event.

  • NESTING_EVENT_TYPE

    The nesting event type. The value is TRANSACTION, STATEMENT, STAGE, or WAIT.

TRUNCATE TABLE is permitted for the events_stages_current table. It removes the rows.

24.10.5.2 The events_stages_history Table

The events_stages_history table contains the most recent N stage events per thread. The value of N is autosized at server startup. To set the table size explicitly, set the performance_schema_events_stages_history_size system variable at server startup. Stage events are not added to the table until they have ended. As new events are added, older events are discarded if the table is full.

The events_stages_history table has the same structure as events_stages_current. See Section 24.10.5.1, “The events_stages_current Table”.

TRUNCATE TABLE is permitted for the events_stages_history table. It removes the rows.

For information about configuration of stage event collection, see Section 24.10.5, “Performance Schema Stage Event Tables”.

24.10.5.3 The events_stages_history_long Table

The events_stages_history_long table contains the most recent N stage events. The value of N is autosized at server startup. To set the table size explicitly, set the performance_schema_events_stages_history_long_size system variable at server startup. Stage events are not added to the table until they have ended. As new events are added, older events are discarded if the table is full. When a thread ends, its rows are removed from the table.

The events_stages_history_long table has the same structure as events_stages_current. See Section 24.10.5.1, “The events_stages_current Table”.

TRUNCATE TABLE is permitted for the events_stages_history_long table. It removes the rows.

For information about configuration of stage event collection, see Section 24.10.5, “Performance Schema Stage Event Tables”.

24.10.6 Performance Schema Statement Event Tables

The Performance Schema instruments statement execution. Statement events occur at a high level of the event hierarchy: Wait events nest within stage events, which nest within statement events, which nest within transaction events.

These tables store statement events:

The following sections describe those tables. There are also summary tables that aggregate information about statement events; see Section 24.10.15.3, “Statement Summary Tables”.

Statement Event Configuration

To enable collection of statement events, enable the relevant instruments and consumers.

The setup_instruments table contains instruments with names that begin with statement. These instruments are enabled by default:

mysql> SELECT * FROM setup_instruments WHERE NAME LIKE 'statement/%';
+---------------------------------------------+---------+-------+
| NAME                                        | ENABLED | TIMED |
+---------------------------------------------+---------+-------+
| statement/sql/select                        | YES     | YES   |
| statement/sql/create_table                  | YES     | YES   |
| statement/sql/create_index                  | YES     | YES   |
...
| statement/sp/stmt                           | YES     | YES   |
| statement/sp/set                            | YES     | YES   |
| statement/sp/set_trigger_field              | YES     | YES   |
| statement/scheduler/event                   | YES     | YES   |
| statement/com/Sleep                         | YES     | YES   |
| statement/com/Quit                          | YES     | YES   |
| statement/com/Init DB                       | YES     | YES   |
...
| statement/abstract/Query                    | YES     | YES   |
| statement/abstract/new_packet               | YES     | YES   |
| statement/abstract/relay_log                | YES     | YES   |
+---------------------------------------------+---------+-------+

To modify collection of statement events, change the ENABLED and TIMING columns of the relevant instruments. For example:

mysql> UPDATE setup_instruments SET ENABLED = 'NO'
       WHERE NAME LIKE 'statement/com/%';

The setup_consumers table contains consumer values with names corresponding to the current and recent statement event table names, and the statement digest consumer. These consumers may be used to filter collection of statement events and statement digesting. events_statements_current, events_statements_history, and statements_digest are enabled by default (before MySQL 5.7.5, events_statements_history is disabled by default):

mysql> SELECT * FROM setup_consumers WHERE NAME LIKE '%statements%';
+--------------------------------+---------+
| NAME                           | ENABLED |
+--------------------------------+---------+
| events_statements_current      | YES     |
| events_statements_history      | YES     |
| events_statements_history_long | NO      |
| statements_digest              | YES     |
+--------------------------------+---------+

To enable all statement consumers, do this:

mysql> UPDATE setup_consumers SET ENABLED = 'YES'
       WHERE NAME LIKE '%statements%';

The setup_timers table contains a row with a NAME value of statement that indicates the unit for statement event timing. The default unit is NANOSECOND.

mysql> SELECT * FROM setup_timers WHERE NAME = 'statement';
+-----------+------------+
| NAME      | TIMER_NAME |
+-----------+------------+
| statement | NANOSECOND |
+-----------+------------+

To change the timing unit, modify the TIMER_NAME value:

mysql> UPDATE setup_timers SET TIMER_NAME = 'MICROSECOND'
       WHERE NAME = 'statement';

For additional information about configuring event collection, see Section 24.3, “Performance Schema Runtime Configuration”.

Statement Monitoring

Statement monitoring begins from the moment the server sees that activity is requested on a thread, to the moment when all activity has ceased. Typically, this means from the time the server gets the first packet from the client to the time the server has finished sending the response. Before MySQL 5.7.2, monitoring occurs only for top-level statements. Statements within stored programs and subqueries are not seen separately. As of 5.7.2, statements within stored programs are monitored like other statements.

When the Performance Schema instruments a request (server command or SQL statement), it uses instrument names that proceed in stages from more general (or abstract) to more specific until it arrives at a final instrument name.

Final instrument names correspond to server commands and SQL statements:

  • Server commands correspond to the COM_xxx codes defined in the mysql_com.h header file and processed in sql/sql_parse.cc. Examples are COM_PING and COM_QUIT. Instruments for commands have names that begin with statement/com, such as statement/com/Ping and statement/com/Quit.

  • SQL statements are expressed as text, such as DELETE FROM t1 or SELECT * FROM t2. Instruments for SQL statements have names that begin with statement/sql, such as statement/sql/delete and statement/sql/select.

Some final instrument names are specific to error handling:

  • statement/com/Error accounts for messages received by the server that are out of band. It can be used to detect commands sent by clients that the server does not understand. This may be helpful for purposes such as identifying clients that are misconfigured or using a version of MySQL more recent than that of the server, or clients that are attempting to attack the server.

  • statement/sql/error accounts for SQL statements that fail to parse. It can be used to detect malformed queries sent by clients. A query that fails to parse differs from a query that parses but fails due to an error during execution. For example, SELECT * FROM is malformed, and the statement/sql/error instrument is used. By contrast, SELECT * parses but fails with a No tables used error. In this case, statement/sql/select is used and the statement event contains information to indicate the nature of the error.

A request can be obtained from any of these sources:

  • As a command or statement request from a client, which sends the request as packets

  • As a statement string read from the relay log on a replication slave (as of MySQL 5.7.2)

  • As an event from the Event Scheduler (as of MySQL 5.7.2)

The details for a request are not initially known and the Performance Schema proceeds from abstract to specific instrument names in a sequence that depends on the source of the request.

For a request received from a client:

  1. When the server detects a new packet at the socket level, a new statement is started with an abstract instrument name of statement/abstract/new_packet.

  2. When the server reads the packet number, it knows more about the type of request received, and the Performance Schema refines the instrument name. For example, if the request is a COM_PING packet, the instrument name becomes statement/com/Ping and that is the final name. If the request is a COM_QUERY packet, it is known to correspond to an SQL statement but not the particular type of statement. In this case, the instrument changes from one abstract name to a more specific but still abstract name, statement/abstract/Query, and the request requires further classification.

  3. If the request is a statement, the statement text is read and given to the parser. After parsing, the exact statement type is known. If the request is, for example, an INSERT statement, the Performance Schema refines the instrument name from statement/abstract/Query to statement/sql/insert, which is the final name.

For a request read as a statement from the relay log on a replication slave:

  1. Statements in the relay log are stored as text and are read as such. There is no network protocol, so the statement/abstract/new_packet instrument is not used. Instead, the initial instrument is statement/abstract/relay_log.

  2. When the statement is parsed, the exact statement type is known. If the request is, for example, an INSERT statement, the Performance Schema refines the instrument name from statement/abstract/Query to statement/sql/insert, which is the final name.

The preceding description applies only for statement-based replication. For row-based replication, table I/O done on the slave as it processes row changes can be instrumented, but row events in the relay log do not appear as discrete statements.

For a request received from the Event Scheduler:

The event execution is instrumented using the name statement/scheduler/event. This is the final name.

Statements executed within the event body are instrumented using statement/sql/* names, without use of any preceding abstract instrument. An event is a stored program, and stored programs are precompiled in memory before execution. Consequently, there is no parsing at runtime and the type of each statement is known by the time it executes.

Statements executed within the event body are child statements. For example, if an event executes an INSERT statement, execution of the event itself is the parent, instrumented using statement/scheduler/event, and the INSERT is the child, instrumented using statement/sql/insert. The parent/child relationship holds between separate instrumented operations. This differs from the sequence of refinement that occurs within a single instrumented operation, from abstract to final instrument names.

For statistics to be collected for statements, it is not sufficient to enable only the final statement/sql/* instruments used for individual statement types. The abtract statement/abstract/* instruments must be enabled as well. This should not normally be an issue because all statement instruments are enabled by default. However, an application that enables or disables statement instruments selectively must take into account that disabling abstract instruments also disables statistics collection for the individual statement instruments. For example, to collect statistics for INSERT statements, statement/sql/insert must be enabled, but also statement/abstract/new_packet and statement/abstract/Query. Similarly, for replicated statements to be instrumented, statement/abstract/relay_log must be enabled.

No statistics are aggregated for abstract instruments such as statement/abstract/Query because no statement is ever classified with an abstract instrument as the final statement name.

The abstract instrument names in the preceding discussion are as of MySQL 5.7.3. In earlier 5.7 versions, there was some renaming before those names were settled on:

  • statement/abstract/new_packet was statement/com/ before MySQL 5.7.3.

  • statement/abstract/Query was statement/com/Query before MySQL 5.7.3.

  • statement/abstract/relay_log was statement/rpl/relay_log in MySQL 5.7.2 and did not exist before that.

24.10.6.1 The events_statements_current Table

The events_statements_current table contains current statement events, one row per thread showing the current status of the thread's most recent monitored statement event.

Of the tables that contain statement event rows, events_statements_current is the most fundamental. Other tables that contain statement event rows are logically derived from the current events. For example, the events_statements_history and events_statements_history_long tables are collections of the most recent statement events, up to a fixed number of rows.

For information about configuration of statement event collection, see Section 24.10.6, “Performance Schema Statement Event Tables”.

The events_statements_current table has these columns:

  • THREAD_ID, EVENT_ID

    The thread associated with the event and the thread current event number when the event starts. The THREAD_ID and EVENT_ID values taken together uniquely identify the row. No two rows have the same pair of values.

  • END_EVENT_ID

    This column is set to NULL when the event starts and updated to the thread current event number when the event ends.

  • EVENT_NAME

    The name of the instrument from which the event was collected. This is a NAME value from the setup_instruments table. Instrument names may have multiple parts and form a hierarchy, as discussed in Section 24.5, “Performance Schema Instrument Naming Conventions”.

    For SQL statements, the EVENT_NAME value initially is statement/com/Query until the statement is parsed, then changes to a more appropriate value, as described in Section 24.10.6, “Performance Schema Statement Event Tables”.

  • SOURCE

    The name of the source file containing the instrumented code that produced the event and the line number in the file at which the instrumentation occurs. This enables you to check the source to determine exactly what code is involved.

  • TIMER_START, TIMER_END, TIMER_WAIT

    Timing information for the event. The unit for these values is picoseconds (trillionths of a second). The TIMER_START and TIMER_END values indicate when event timing started and ended. TIMER_WAIT is the event elapsed time (duration).

    If an event has not finished, TIMER_END and TIMER_WAIT are NULL before MySQL 5.7.8. As of 5.7.8, TIMER_END is the current timer value and TIMER_WAIT is the time elapsed so far (TIMER_ENDTIMER_START).

    If an event is produced from an instrument that has TIMED = NO, timing information is not collected, and TIMER_START, TIMER_END, and TIMER_WAIT are all NULL.

    For discussion of picoseconds as the unit for event times and factors that affect time values, see Section 24.3.1, “Performance Schema Event Timing”.

  • LOCK_TIME

    The time spent waiting for table locks. This value is computed in microseconds but normalized to picoseconds for easier comparison with other Performance Schema timers.

  • SQL_TEXT

    The text of the SQL statement. For a command not associated with an SQL statement, the value is NULL.

    As of MySQL 5.7.6, the maximum number of bytes to display can be changed by changing the performance_schema_max_sql_text_length system variable at server startup. Before 5.7.6, the maximum is fixed at 1024.

  • DIGEST

    The statement digest MD5 value as a string of 32 hexadecimal characters, or NULL if the statement_digest consumer is no. For more information about statement digesting, see Section 24.8, “Performance Schema Statement Digests”.

  • DIGEST_TEXT

    The normalized statement digest text, or NULL if the statement_digest consumer is no. For more information about statement digesting, see Section 24.8, “Performance Schema Statement Digests”.

    The performance_schema_max_digest_length system variable determines the maximum number of bytes available for computing statement digests. However, the display length of statement digests may be longer than the available buffer size due to encoding of statement components such as keywords and literal values in digest buffer. Consequently, values selected from the DIGEST_TEXT column of statement event tables may appear to exceed the performance_schema_max_digest_length value.

    This variable was added in MySQL 5.7.8. In MySQL 5.7.6 and 5.7.7, use max_digest_length instead. Before 5.7.6, the value cannot be changed.

  • CURRENT_SCHEMA

    The default database for the statement, NULL if there is none.

  • OBJECT_SCHEMA, OBJECT_NAME, OBJECT_TYPE

    For nested statements (stored programs), these columns contain information about the parent statement. Otherwise they are NULL.

  • OBJECT_INSTANCE_BEGIN

    This column identifies the statement. The value is the address of an object in memory.

  • MYSQL_ERRNO

    The statement error number, from the statement diagnostics area.

  • RETURNED_SQLSTATE

    The statement SQLSTATE value, from the statement diagnostics area.

  • MESSAGE_TEXT

    The statement error message, from the statement diagnostics area.

  • ERRORS

    Whether an error occurred for the statement. The value is 0 if the SQLSTATE value begins with 00 (completion) or 01 (warning). The value is 1 is the SQLSTATE value is anything else.

  • WARNINGS

    The number of warnings, from the statement diagnostics area.

  • ROWS_AFFECTED

    The number of rows affected by the statement. For a description of the meaning of affected, see Section 26.8.7.1, “mysql_affected_rows()”.

  • ROWS_SENT

    The number of rows returned by the statement.

  • ROWS_EXAMINED

    The number of rows read from storage engines during statement execution.

  • CREATED_TMP_DISK_TABLES

    Like the Created_tmp_disk_tables status variable, but specific to the statement.

  • CREATED_TMP_TABLES

    Like the Created_tmp_tables status variable, but specific to the statement.

  • SELECT_FULL_JOIN

    Like the Select_full_join status variable, but specific to the statement.

  • SELECT_FULL_RANGE_JOIN

    Like the Select_full_range_join status variable, but specific to the statement.

  • SELECT_RANGE

    Like the Select_range status variable, but specific to the statement.

  • SELECT_RANGE_CHECK

    Like the Select_range_check status variable, but specific to the statement.

  • SELECT_SCAN

    Like the Select_scan status variable, but specific to the statement.

  • SORT_MERGE_PASSES

    Like the Sort_merge_passes status variable, but specific to the statement.

  • SORT_RANGE

    Like the Sort_range status variable, but specific to the statement.

  • SORT_ROWS

    Like the Sort_rows status variable, but specific to the statement.

  • SORT_SCAN

    Like the Sort_scan status variable, but specific to the statement.

  • NO_INDEX_USED

    1 if the statement performed a table scan without using an index, 0 otherwise.

  • NO_GOOD_INDEX_USED

    1 if the server found no good index to use for the statement, 0 otherwise. For additional information, see the description of the Extra column from EXPLAIN output for the Range checked for each record value in Section 9.8.2, “EXPLAIN Output Format”.

  • NESTING_EVENT_ID, NESTING_EVENT_TYPE, NESTING_EVENT_LEVEL

    Before MySQL 5.7.2, only NESTING_EVENT_ID and NESTING_EVENT_TYPE exist and are always NULL.

    As of MySQL 5.7.2, all three columns exist and are used with other columns to provide information as follows for top-level (unnested) statements and nested statements (executed within a stored program).

    For top level statements:

    OBJECT_TYPE = NULL
    OBJECT_SCHEMA = NULL
    OBJECT_NAME = NULL
    NESTING_EVENT_ID = NULL
    NESTING_EVENT_TYPE = NULL
    NESTING_LEVEL = 0
    

    For nested statements:

    OBJECT_TYPE = the parent statement object type
    OBJECT_SCHEMA = the parent statement object schema
    OBJECT_NAME = the parent statement object name
    NESTING_EVENT_ID = the parent statement EVENT_ID
    NESTING_EVENT_TYPE = 'STATEMENT'
    NESTING_LEVEL = the parent statement NESTING_LEVEL plus one
    

TRUNCATE TABLE is permitted for the events_statements_current table. It removes the rows.

24.10.6.2 The events_statements_history Table

The events_statements_history table contains the most recent N statement events per thread. The value of N is autosized at server startup. To set the table size explicitly, set the performance_schema_events_statements_history_size system variable at server startup. Statement events are not added to the table until they have ended. As new events are added, older events are discarded if the table is full.

The events_statements_history table has the same structure as events_statements_current. See Section 24.10.6.1, “The events_statements_current Table”.

TRUNCATE TABLE is permitted for the events_statements_history table. It removes the rows.

For information about configuration of statement event collection, see Section 24.10.6, “Performance Schema Statement Event Tables”.

24.10.6.3 The events_statements_history_long Table

The events_statements_history_long table contains the most recent N statement events. The value of N is autosized at server startup. To set the table size explicitly, set the performance_schema_events_statements_history_long_size system variable at server startup. Statement events are not added to the table until they have ended. As new events are added, older events are discarded if the table is full. When a thread ends, its rows are removed from the table.

The events_statements_history_long table has the same structure as events_statements_current. See Section 24.10.6.1, “The events_statements_current Table”.

TRUNCATE TABLE is permitted for the events_statements_history_long table. It removes the rows.

For information about configuration of statement event collection, see Section 24.10.6, “Performance Schema Statement Event Tables”.

24.10.6.4 The prepared_statements_instances Table

As of MySQL 5.7.4, the Performance Schema provides instrumentation for prepared statements, for which there are two protocols:

  • The binary protocol. This is accessed through the MySQL C API and maps onto underlying server commands as shown in the following table.

    C API FunctionCorresponding Server Command
    mysql_stmt_prepare()COM_STMT_PREPARE
    mysql_stmt_execute()COM_STMT_EXECUTE
    mysql_stmt_close()COM_STMT_CLOSE
  • The text protocol. This is accessed using SQL statements and maps onto underlying server commands as shown in the following table.

    SQL StatementCorresponding Server Command
    PREPARESQLCOM_PREPARE
    EXECUTESQLCOM_EXECUTE
    DEALLOCATE PREPARE, DROP PREPARESQLCOM_DEALLOCATE PREPARE

Performance Schema prepared statement instrumentation covers both protocols. The following discussion refers to the server commands rather than the C API functions or SQL statements.

Information about prepared statements is available in the prepared_statements_instances table. This table enables inspection of prepared statements used in the server and provides aggregated statistics about them. To control the size of this table, set the performance_schema_max_prepared_statements_instances system variable at server startup.

Collection of prepared statement information depends on the statement instruments shown in the following table. These instruments are enabled by default. To modify them, update the setup_instruments table.

InstrumentServer Command
statement/com/PrepareCOM_STMT_PREPARE
statement/com/ExecuteCOM_STMT_EXECUTE
statement/sql/prepare_sqlSQLCOM_PREPARE
statement/sql/execute_sqlSQLCOM_EXECUTE

The Performance Schema manages the contents of the prepared_statements_instances table as follows:

  • Statement preparation

    A COM_STMT_PREPARE or SQLCOM_PREPARE command creates a prepared statement in the server. If the statement is successfully instrumented, a new row is added to the prepared_statements_instances table. If the statement cannot be instrumented, Performance_schema_prepared_statements_lost status variable is incremented.

  • Prepared statement execution

    Execution of a COM_STMT_EXECUTE or SQLCOM_PREPARE command for an instrumented prepared statement instance updates the corresponding prepared_statements_instances table row.

  • Prepared statement deallocation

    Execution of a COM_STMT_CLOSE or SQLCOM_DEALLOCATE_PREPARE command for an instrumented prepared statement instance removes the corresponding prepared_statements_instances table row. To avoid resource leaks, removal occurs even if the prepared statement instruments described previously are disabled.

The prepared_statements_instances table has these columns:

  • OBJECT_INSTANCE_BEGIN

    The address in memory of the instrumented prepared statement.

  • STATEMENT_ID

    The internal statement ID assigned by the server. The text and binary protocols both use statement IDs.

  • STATEMENT_NAME

    For the binary protocol, this column is NULL. For the text protocol, this column is the external statement name assigned by the user. For example, for the following SQL statement, the name of the prepared statement is stmt:

    PREPARE stmt FROM 'SELECT 1';
    
  • SQL_TEXT

    The prepared statement text, with ? placeholder markers.

  • OWNER_THREAD_ID, OWNER_EVENT_ID

    These columns indicate the event that created the prepared statement.

  • OWNER_OBJECT_TYPE, OWNER_OBJECT_SCHEMA, OWNER_OBJECT_NAME

    For a prepared statement created by a client session, these columns are NULL. For a prepared statement created by a stored program, these columns point to the stored program. A typical user error is forgetting to deallocate prepared statements. These columns can be used to find stored programs that leak prepared statements:

    SELECT OWNER_OBJECT_TYPE, OWNER_OBJECT_SCHEMA, OWNER_OBJECT_NAME,
    STATEMENT_NAME, SQL_TEXT
    FROM performance_schema.prepared_statements_instances
    WHERE OWNER_OBJECT_TYPE IS NOT NULL;
    
  • TIMER_PREPARE

    The time spent executing the statement preparation itself.

  • COUNT_REPREPARE

    The number of times the statement was reprepared internally (see Section 9.10.4, “Caching of Prepared Statements and Stored Programs”). Timing statistics for repreparation are not available because it is counted as part of statement execution, not as a separate operation.

  • COUNT_EXECUTE, SUM_TIMER_EXECUTE, MIN_TIMER_EXECUTE, AVG_TIMER_EXECUTE, MAX_TIMER_EXECUTE

    Aggregated statistics for executions of the prepared statement.

  • SUM_xxx

    The remaining SUM_xxx columns are the same as for the statement summary tables (see Section 24.10.15.3, “Statement Summary Tables”).

TRUNCATE TABLE resets the statistics columns of the prepared_statements_instances table.

24.10.7 Performance Schema Transaction Tables

As of MySQL 5.7.3, the Performance Schema instruments transactions. Within the event hierarchy, wait events nest within stage events, which nest within statement events, which nest within transaction events.

These tables store transaction events:

The following sections describe those tables. There are also summary tables that aggregate information about transaction events; see Section 24.10.15.4, “Transaction Summary Tables”.

Transaction Event Configuration

To enable collection of transaction events, enable the relevant instruments and consumers.

The setup_instruments table contains an instrument named transaction. This instrument is disabled by default:

mysql> SELECT * FROM setup_instruments WHERE NAME = 'transaction';
+-------------+---------+-------+
| NAME        | ENABLED | TIMED |
+-------------+---------+-------+
| transaction | NO      | NO    |
+-------------+---------+-------+

To enable collection of transaction events, including timing information, do this:

mysql> UPDATE setup_instruments SET ENABLED = 'YES', TIMED = 'YES'
       WHERE NAME = 'transaction';

The setup_consumers table contains consumer values with names corresponding to the current and recent transaction event table names. These consumers may be used to filter collection of transaction events:

mysql> SELECT * FROM setup_consumers WHERE NAME LIKE '%transactions%';
+----------------------------------+---------+
| NAME                             | ENABLED |
+----------------------------------+---------+
| events_transactions_current      | NO      |
| events_transactions_history      | NO      |
| events_transactions_history_long | NO      |
+----------------------------------+---------+

To enable all transaction consumers, do this:

mysql> UPDATE setup_consumers SET ENABLED = 'YES'
       WHERE NAME LIKE '%transactions%';

To enable collection of transaction events only for specific transaction event tables, enable the corresponding transaction consumers.

The setup_timers table contains a row with a NAME value of transaction that indicates the unit for transaction event timing. The default unit is NANOSECOND.

mysql> SELECT * FROM setup_timers WHERE NAME = 'transaction';
+-------------+------------+
| NAME        | TIMER_NAME |
+-------------+------------+
| transaction | NANOSECOND |
+-------------+------------+

To change the timing unit, modify the TIMER_NAME value:

mysql> UPDATE setup_timers SET TIMER_NAME = 'MICROSECOND'
       WHERE NAME = 'transaction';

For additional information about configuring event collection, see Section 24.3, “Performance Schema Runtime Configuration”.

Transaction Boundaries

In MySQL Server, transactions start explicitly with these statements:

START TRANSACTION | BEGIN | XA START | XA BEGIN

Transactions also start implicitly. For example, when the autocommit system variable is enabled, the start of each statement starts a new transaction.

When autocommit is disabled, the first statement following a committed transaction marks the start of a new transaction. Subsequent statements are part of the transaction until it is committed.

Transactions explicitly end with these statements:

COMMIT | ROLLBACK | XA COMMIT | XA ROLLBACK

Transactions also end implicitly, by execution of DDL statements, locking statements, and server administration statements.

In the following discussion, references to START TRANSACTION also apply to BEGIN, XA START, and XA BEGIN. Similarly, references to COMMIT and ROLLBACK apply to XA COMMIT and XA ROLLBACK, respectively.

The Performance Schema defines transaction boundaries similarly to that of the server. The start and end of a transaction event closely match the corresponding state transitions in the server:

  • For an explicitly started transaction, the transaction event starts during processing of the START TRANSACTION statement.

  • For an implicitly started transaction, the transaction event starts on the first statement that uses a transactional engine after the previous transaction has ended.

  • For any transaction, whether explicitly or implicitly ended, the transaction event ends when the server transitions out of the active transaction state during the processing of COMMIT or ROLLBACK.

There are subtle implications to this approach:

  • Transaction events in the Performance Schema do not fully include the statement events associated with the corresponding START TRANSACTION, COMMIT, or ROLLBACK statements. There is a trivial amount of timing overlap between the transaction event and these statements.

  • Statements that work with nontransactional engines have no effect on the transaction state of the connection. For implicit transactions, the transaction event begins with the first statement that uses a transactional engine. This means that statements operating exclusively on nontransactional tables are ignored, even following START TRANSACTION.

To illustrate, consider the following scenario:

1. SET autocommit = OFF;
2. CREATE TABLE t1 (a INT) ENGINE = InnoDB;
3. START TRANSACTION;                       -- Transaction 1 START
4. INSERT INTO t1 VALUES (1), (2), (3);
5. CREATE TABLE t2 (a INT) ENGINE = MyISAM; -- Transaction 1 COMMIT
                                            -- (implicit; DDL forces commit)
6. INSERT INTO t2 VALUES (1), (2), (3);     -- Update nontransactional table
7. UPDATE t2 SET a = a + 1;                 -- ... and again
8. INSERT INTO t1 VALUES (4), (5), (6);     -- Write to transactional table
                                            -- Transaction 2 START (implicit)
9. COMMIT;                                  -- Transaction 2 COMMIT

From the perspective of the server, Transaction 1 ends when table t2 is created. Transaction 2 does not start until a transactional table is accessed, despite the intervening updates to nontransactional tables.

From the perspective of the Performance Schema, Transaction 2 starts when the server transitions into an active transaction state. Statements 6 and 7 are not included within the boundaries of Transaction 2, which is consistent with how the server writes transactions to the binary log.

Transaction Instrumentation

Three attributes define transactions:

To reduce complexity of the transaction instrumentation and to ensure that the collected transaction data provides complete, meaningful results, all transactions are instrumented independently of access mode, isolation level, or autocommit mode.

To selectively examine transaction history, use the attribute columns in the transaction event tables: ACCESS_MODE, ISOLATION_LEVEL, and AUTOCOMMIT.

The cost of transaction instrumentation can be reduced various ways, such as enabling or disabling transaction instrumentation according to user, account, host, or thread (client connection).

Transactions and Nested Events

The parent of a transaction event is the event that initiated the transaction. For an explicitly started transaction, this includes the START TRANSACTION and COMMIT AND CHAIN statements. For an implicitly started transaction, it is the first statement that uses a transactional engine after the previous transaction ends.

In general, a transaction is the top-level parent to all events initiated during the transaction, including statements that explicitly end the transaction such as COMMIT and ROLLBACK. Exceptions are statements that implicitly end a transaction, such as DDL statements, in which case the current transaction must be committed before the new statement is executed.

Transactions and Stored Programs

Transactions and stored program events are related as follows:

  • Stored Procedures

    Stored procedures operate independently of transactions. A stored procedure can be started within a transaction, and a transaction can be started or ended from within a stored procedure. If called from within a transaction, a stored procedure can execute statements that force a commit of the parent transaction and then start a new transaction.

    If a stored procedure is started within a transaction, that transaction is the parent of the stored procedure event.

    If a transaction is started by a stored procedure, the stored procedure is the parent of the transaction event.

  • Stored Functions

    Stored functions are restricted from causing an explicit or implicit commit or rollback. Stored function events can reside within a parent transaction event.

  • Triggers

    Triggers activate as part of a statement that accesses the table with which it is associated, so the parent of a trigger event is always the statement that activates it.

    Triggers cannot issue statements that cause an explicit or implicit commit or rollback of a transaction.

  • Scheduled Events

    The execution of the statements in the body of a scheduled event takes place in a new connection. Nesting of a scheduled event within a parent transaction is not applicable.

Transactions and Savepoints

Savepoint statements are recorded as separate statement events. Transaction events include separate counters for SAVEPOINT, ROLLBACK TO SAVEPOINT, and RELEASE SAVEPOINT statements issued during the transaction.

Transactions and Errors

Errors and warnings that occur within a transaction are recorded in statement events, but not in the corresponding transaction event. This includes transaction-specific errors and warnings, such as a rollback on a nontransactional table or GTID consistency errors.

24.10.7.1 The events_transactions_current Table

The events_transactions_current table (added in MySQL 5.7.3) contains current transaction events, one row per thread showing the current status of the thread's most recent monitored transaction event. For example:

mysql> SELECT * FROM events_transactions_current LIMIT 1\G
*************************** 1. row ***************************
                      THREAD_ID: 26
                       EVENT_ID: 7
                   END_EVENT_ID: NULL
                     EVENT_NAME: transaction
                          STATE: ACTIVE
                         TRX_ID: NULL
                           GTID: 3E11FA47-71CA-11E1-9E33-C80AA9429562:56
                            XID: NULL
                       XA_STATE: NULL
                         SOURCE: transaction.cc:150
                    TIMER_START: 420833537900000
                      TIMER_END: NULL
                     TIMER_WAIT: NULL
                    ACCESS_MODE: READ WRITE
                ISOLATION_LEVEL: REPEATABLE READ
                     AUTOCOMMIT: NO
           NUMBER_OF_SAVEPOINTS: 0
NUMBER_OF_ROLLBACK_TO_SAVEPOINT: 0
    NUMBER_OF_RELEASE_SAVEPOINT: 0
          OBJECT_INSTANCE_BEGIN: NULL
               NESTING_EVENT_ID: 6
             NESTING_EVENT_TYPE: STATEMENT

Of the tables that contain transaction event rows, events_transactions_current is the most fundamental. Other tables that contain transaction event rows are logically derived from the current events. For example, the events_transactions_history and events_transactions_history_long tables are collections of the most recent transaction events, up to a fixed number of rows.

For information about configuration of transaction event collection, see Section 24.10.7, “Performance Schema Transaction Tables”.

The events_transactions_current table has these columns:

  • THREAD_ID, EVENT_ID

    The thread associated with the event and the thread current event number when the event starts. The THREAD_ID and EVENT_ID values taken together uniquely identify the row. No two rows have the same pair of values.

  • END_EVENT_ID

    This column is set to NULL when the event starts and updated to the thread current event number when the event ends.

  • EVENT_NAME

    The name of the instrument from which the event was collected. This is a NAME value from the setup_instruments table. Instrument names may have multiple parts and form a hierarchy, as discussed in Section 24.5, “Performance Schema Instrument Naming Conventions”.

  • STATE

    The current transaction state. The value is ACTIVE (after START TRANSACTION or BEGIN), COMMITTED (after COMMIT), or ROLLED BACK (after ROLLBACK).

  • TRX_ID

    Unused.

  • GTID

    This column changed in MySQL 5.7.6.

    • Versions of MySQL prior to 5.7.6:

      If gtid_mode=OFF, the value is NULL. If gtid_mode=ON, this is the value of gtid_next when the transaction started. If gtid_next=AUTOMATIC the value is AUTOMATIC, otherwise the value is a GTID in UUID:NUMBER format.

    • Versions of MySQL 5.7.6 and later:

      The GTID column contains the value of gtid_next, which can be one of ANONYMOUS, AUTOMATIC, or a GTID using the format UUID:NUMBER. For transactions that use gtid_next=AUTOMATIC, which is all normal client transactions, the GTID column changes when the transaction commits and the actual GTID is assigned. If gtid_mode is either ON or ON_PERMISSIVE, the GTID column changes to the transaction's GTID. If gtid_mode is either OFF or OFF_PERMISSIVE, the GTID column changes to ANONYMOUS.

  • XID

    The XA transaction identifier. It has the format described in Section 14.3.7.1, “XA Transaction SQL Syntax”. This column was removed in MySQL 5.7.7 and replaced with the XID_FORMAT_ID, XID_GTRID, and XID_BQUAL columns representing the components of XID values.

  • XID_FORMAT_ID, XID_GTRID, and XID_BQUAL

    The components of the XA transaction identifier. They have the format described in Section 14.3.7.1, “XA Transaction SQL Syntax”. These columns were added in MySQL 5.7.7 as replacements for the XID column.

  • XA_STATE

    The state of the XA transaction. The value is ACTIVE (after XA START), IDLE (after XA END), PREPARED (after XA PREPARE), ROLLED BACK (after XA ROLLBACK), or COMMITTED (after XA COMMIT).

  • SOURCE

    The name of the source file containing the instrumented code that produced the event and the line number in the file at which the instrumentation occurs. This enables you to check the source to determine exactly what code is involved.

  • TIMER_START, TIMER_END, TIMER_WAIT

    Timing information for the event. The unit for these values is picoseconds (trillionths of a second). The TIMER_START and TIMER_END values indicate when event timing started and ended. TIMER_WAIT is the event elapsed time (duration).

    If an event has not finished, TIMER_END and TIMER_WAIT are NULL before MySQL 5.7.8. As of 5.7.8, TIMER_END is the current timer value and TIMER_WAIT is the time elapsed so far (TIMER_ENDTIMER_START).

    If an event is produced from an instrument that has TIMED = NO, timing information is not collected, and TIMER_START, TIMER_END, and TIMER_WAIT are all NULL.

    For discussion of picoseconds as the unit for event times and factors that affect time values, see Section 24.3.1, “Performance Schema Event Timing”.

  • ACCESS_MODE

    The transaction access mode. The value is READ ONLY or READ WRITE.

  • ISOLATION_LEVEL

    The transaction isolation level. The value is REPEATABLE READ, READ COMMITTED, READ UNCOMMITTED, or SERIALIZABLE.

  • AUTOCOMMIT

    Whether autcommit mode was enabled when the transaction started.

  • NUMBER_OF_SAVEPOINTS, NUMBER_OF_ROLLBACK_TO_SAVEPOINT, NUMBER_OF_RELEASE_SAVEPOINT

    The number of SAVEPOINT, ROLLBACK TO SAVEPOINT, and RELEASE SAVEPOINT statements issued during the transaction.

  • OBJECT_INSTANCE_BEGIN

    Unused.

  • NESTING_EVENT_ID

    The EVENT_ID value of the event within which this event is nested.

  • NESTING_EVENT_TYPE

    The nesting event type. The value is TRANSACTION, STATEMENT, STAGE, or WAIT. (TRANSACTION will not appear because transactions cannot be nested.)

TRUNCATE TABLE is permitted for the events_transactions_current table. It removes the rows.

24.10.7.2 The events_transactions_history Table

The events_transactions_history table (added in MySQL 5.7.3) contains the most recent N transaction events per thread. The value of N is autosized at server startup. To set the table size explicitly, set the performance_schema_events_transactions_history_size system variable at server startup. Transaction events are not added to the table until they have ended. As new events are added, older events are discarded if the table is full.

The events_transactions_history table has the same structure as events_transactions_current. See Section 24.10.7.1, “The events_transactions_current Table”.

TRUNCATE TABLE is permitted for the events_transactions_history table. It removes the rows.

For information about configuration of transaction event collection, see Section 24.10.7, “Performance Schema Transaction Tables”.

24.10.7.3 The events_transactions_history_long Table

The events_transactions_history_long table (added in MySQL 5.7.3) contains the most recent N transaction events. The value of N is autosized at server startup. To set the table size explicitly, set the performance_schema_events_transactions_history_long_size system variable at server startup. Transaction events are not added to the table until they have ended. As new events are added, older events are discarded if the table is full. When a thread ends, its rows are removed from the table.

The events_transactions_history_long table has the same structure as events_transactions_current. See Section 24.10.7.1, “The events_transactions_current Table”.

TRUNCATE TABLE is permitted for the events_transactions_history_long table. It removes the rows.

For information about configuration of transaction event collection, see Section 24.10.7, “Performance Schema Transaction Tables”.

24.10.8 Performance Schema Connection Tables

When a client connects to the MySQL server, it does so under a particular user name and from a particular host. The Performance Schema provides statistics about these connections, tracking them per account (user and host combination) as well as separately per user name and per host name, using these tables:

  • accounts: Connection statistics per client account

  • hosts: Connection statistics per client host name

  • users: Connection statistics per client user name

The meaning of account in the connection tables is similar to its meaning in the MySQL grant tables in the mysql system database, in the sense that the term refers to a combination of user and host values. They differ in that, for grant tables, the host part of an account can be a pattern, whereas for Performance Schema tables, the host value is always a specific nonpattern host name.

Each connection table has CURRENT_CONNECTIONS and TOTAL_CONNECTIONS columns to track the current and total number of connections per tracking value on which its statistics are based. The tables differ in what they use for the tracking value. The accounts table has USER and HOST columns to track connections per user and host combination. The users and hosts tables have a USER and HOST column, respectively, to track connections per user name and per host name.

The Performance Schema also counts internal threads and threads for user sessions that failed to authenticate, using rows with USER and HOST column values of NULL.

Suppose that clients named user1 and user2 each connect one time from hosta and hostb. The Performance Schema tracks the connections as follows:

  • The accounts table has four rows, for the user1/hosta, user1/hostb, user2/hosta, and user2/hostb account values, each row counting one connection per account.

  • The hosts table has two rows, for hosta and hostb, each row counting two connections per host name.

  • The users table has two rows, for user1 and user2, each row counting two connections per user name.

When a client connects, the Performance Schema determines which row in each connection table applies, using the tracking value appropriate to each table. If there is no such row, one is added. Then the Performance Schema increments by one the CURRENT_CONNECTIONS and TOTAL_CONNECTIONS columns in that row.

When a client disconnects, the Performance Schema decrements by one the CURRENT_CONNECTIONS column in the row and leaves the TOTAL_CONNECTIONS column unchanged.

TRUNCATE TABLE is permitted for connection tables. It has these effects:

  • Rows are removed for accounts, hosts, or users that have no current connections (rows with CURRENT_CONNECTIONS = 0).

  • Nonremoved rows are reset to count only current connections: For rows with CURRENT_CONNECTIONS > 0, TOTAL_CONNECTIONS is reset to CURRENT_CONNECTIONS.

  • Summary tables that depend on the connection table are implicitly truncated, as described later in this section.

The Performance Schema maintains summary tables that aggregate connection statistics for various event types by account, host, or user. These tables have _summary_by_account, _summary_by_host, or _summary_by_user in the name. To identify them, use this query:

mysql> SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES
       WHERE TABLE_SCHEMA = 'performance_schema'
       AND TABLE_NAME REGEXP '_summary_by_(account|host|user)'
       ORDER BY TABLE_NAME;
+------------------------------------------------------+
| TABLE_NAME                                           |
+------------------------------------------------------+
| events_stages_summary_by_account_by_event_name       |
| events_stages_summary_by_host_by_event_name          |
| events_stages_summary_by_user_by_event_name          |
| events_statements_summary_by_account_by_event_name   |
| events_statements_summary_by_host_by_event_name      |
| events_statements_summary_by_user_by_event_name      |
| events_transactions_summary_by_account_by_event_name |
| events_transactions_summary_by_host_by_event_name    |
| events_transactions_summary_by_user_by_event_name    |
| events_waits_summary_by_account_by_event_name        |
| events_waits_summary_by_host_by_event_name           |
| events_waits_summary_by_user_by_event_name           |
| memory_summary_by_account_by_event_name              |
| memory_summary_by_host_by_event_name                 |
| memory_summary_by_user_by_event_name                 |
+------------------------------------------------------+

For details about individual connection summary tables, consult the section that describes tables for the summarized event type:

TRUNCATE TABLE is permitted for connection summary tables. It removes rows for accounts, hosts, or users with no connections, and resets the summary columns to zero for the remaining rows. In addition, each summary table that is aggregated by account, host, user, or thread is implicitly truncated by truncation of the connection table on which it depends. The following table describes the relationship between connection table truncation and implicitly truncated tables.

Table 24.2 Implicit Effects of Connection Table Truncation

Truncated Connection TableImplicitly Truncated Summary Tables
accountsTables with names containing _summary_by_account, _summary_by_thread
hostsTables with names containing _summary_by_account, _summary_by_host, _summary_by_thread
usersTables with names containing _summary_by_account, _summary_by_user, _summary_by_thread

Truncating a _summary_global summary table also implicitly truncates its corresponding connection and thread summary tables. For example, truncating events_waits_summary_global_by_event_name implicitly truncates the wait event summary tables that are aggregated by account, host, user, or thread.

24.10.8.1 The accounts Table

The accounts table contains a row for each account that has connected to the MySQL server. For each account, the table counts the current and total number of connections. The table size is autosized at server startup. To set the table size explicitly, set the performance_schema_accounts_size system variable at server startup. To disable account statistics, set this variable to 0.

The accounts table has the following columns. For a description of how the Performance Schema maintains rows in this table, including the effect of TRUNCATE TABLE, see Section 24.10.8, “Performance Schema Connection Tables”.

  • USER

    The client user name for the connection. This is NULL for an internal thread, or for a user session that failed to authenticate.

  • HOST

    The host from which the client connected. This is NULL for an internal thread, or for a user session that failed to authenticate.

  • CURRENT_CONNECTIONS

    The current number of connections for the account.

  • TOTAL_CONNECTIONS

    The total number of connections for the account.

24.10.8.2 The hosts Table

The hosts table contains a row for each host from which clients have connected to the MySQL server. For each host name, the table counts the current and total number of connections. The table size is autosized at server startup. To set the table size explicitly, set the performance_schema_hosts_size system variable at server startup. To disable host statistics, set this variable to 0.

The hosts table has the following columns. For a description of how the Performance Schema maintains rows in this table, including the effect of TRUNCATE TABLE, see Section 24.10.8, “Performance Schema Connection Tables”.

  • HOST

    The host from which the client connected. This is NULL for an internal thread, or for a user session that failed to authenticate.

  • CURRENT_CONNECTIONS

    The current number of connections for the host.

  • TOTAL_CONNECTIONS

    The total number of connections for the host.

24.10.8.3 The users Table

The users table contains a row for each user who has connected to the MySQL server. For each user name, the table counts the current and total number of connections. The table size is autosized at server startup. To set the table size explicitly, set the performance_schema_users_size system variable at server startup. To disable user statistics, set this variable to 0.

The users table has the following columns. For a description of how the Performance Schema maintains rows in this table, including the effect of TRUNCATE TABLE, see Section 24.10.8, “Performance Schema Connection Tables”.

  • USER

    The client user name for the connection. This is NULL for an internal thread, or for a user session that failed to authenticate.

  • CURRENT_CONNECTIONS

    The current number of connections for the user.

  • TOTAL_CONNECTIONS

    The total number of connections for the user.

24.10.9 Performance Schema Connection Attribute Tables

Application programs can provide key/value pairs as connection attributes to be passed to the server at connect time. For the C API, define the attribute set using the mysql_options() and mysql_options4() functions. Other MySQL Connectors may provide their own attribute-definition methods.

These tables expose attribute information:

Attribute names that begin with an underscore (_) are reserved for internal use and should not be created by application programs. This convention permits new attributes to be introduced by MySQL without colliding with application attributes.

The set of connection attributes visible on a given connection varies depending on your platform and MySQL Connector used to establish the connection.

The libmysqlclient client library (provided in MySQL and MySQL Connector/C distributions) sets these attributes:

  • _client_name: The client name (libmysql for the client library)

  • _client_version: The client library version

  • _os: The operating system (for example, Linux, Win64)

  • _pid: The client process ID

  • _platform: The machine platform (for example, x86_64)

  • _thread: The client thread ID (Windows only)

Other MySQL Connectors may define their own connection attributes.

MySQL Connector/J defines these attributes:

  • _client_license: The connector license type

  • _runtime_vendor: The Java runtime environment (JRE) vendor

  • _runtime_version: The Java runtime environment (JRE) version

MySQL Connector/Net defines these attributes:

  • _client_version: The client library version

  • _os: The operating system (for example, Linux, Win64)

  • _pid: The client process ID

  • _platform: The machine platform (for example, x86_64)

  • _program_name: The client name

  • _thread: The client thread ID (Windows only)

PHP defines attributes that depend on how it was compiled:

  • Compiled using libmysqlclient: The standard libmysqlclient attributes, described previously

  • Compiled using mysqlnd: Only the _client_name attribute, with a value of mysqlnd

Many MySQL client programs set a program_name attribute with a value equal to the client name. For example, mysqladmin and mysqldump set program_name to mysqladmin and mysqldump, respectively.

Some MySQL client programs define additional attributes:

  • mysqlbinlog defines the _client_role attribute as binary_log_listener.

  • Replication slave connections define program_name as mysqld, _client_role as binary_log_listener, and _client_replication_channel_name as the channel name.

  • FEDERATED storage engine connections define program_name as mysqld and _client_role as federated_storage.

There are limits on the amount of connection attribute data transmitted from client to server: A fixed limit imposed by the client prior to connect time; a fixed limit imposed by the server at connect time; and a configurable limit imposed by the Performance Schema at connect time.

For connections initiated using the C API, the libmysqlclient library imposes a limit of 64KB on the aggregate size of connection attribute data on the client side: Calls to mysql_options() that cause this limit to be exceeded produce a CR_INVALID_PARAMETER_NO error. Other MySQL Connectors may impose their own client-side limits on how much connection attribute data can be transmitted to the server.

On the server side, these size checks on connection attribute data occur:

  • The server imposes a limit of 64KB on the aggregate size of connection attribute data it will accept. If a client attempts to send more than 64KB of attribute data, the server rejects the connection.

  • For accepted connections, the Performance Schema checks aggregate attribute size against the value of the performance_schema_session_connect_attrs_size system variable. If attribute size exceeds this value, these actions take place:

    • The Performance Schema truncates the attribute data and increments the Performance_schema_session_connect_attrs_lost status variable, which indicates the number of connections for which attribute truncation occurred.

    • The Performance Schema writes a message to the error log if the log_warnings system variable is greater than zero:

      [Warning] Connection attributes of length N were truncated
      

24.10.9.1 The session_account_connect_attrs Table

Application programs can provide key/value connection attributes to be passed to the server at connect time, using the mysql_options() and mysql_options4() C API functions. For descriptions of common attributes, see Section 24.10.9, “Performance Schema Connection Attribute Tables”.

The session_account_connect_attrs table contains connection attributes only for sessions for your own account. To see connection attributes for all sessions, look in the session_connect_attrs table.

The session_account_connect_attrs table contains these columns:

  • PROCESSLIST_ID

    The connection identifier for the session.

  • ATTR_NAME

    The attribute name.

  • ATTR_VALUE

    The attribute value.

  • ORDINAL_POSITION

    The order in which the attribute was added to the set of connection attributes.

TRUNCATE TABLE is not permitted for the session_account_connect_attrs table.

24.10.9.2 The session_connect_attrs Table

Application programs can provide key/value connection attributes to be passed to the server at connect time, using the mysql_options() and mysql_options4() C API functions. For descriptions of common attributes, see Section 24.10.9, “Performance Schema Connection Attribute Tables”.

The session_connect_attrs table contains connection attributes for all sessions. To see connection attributes only for sessions for your own account, look in the session_account_connect_attrs table.

The session_connect_attrs table contains these columns:

  • PROCESSLIST_ID

    The connection identifier for the session.

  • ATTR_NAME

    The attribute name.

  • ATTR_VALUE

    The attribute value.

  • ORDINAL_POSITION

    The order in which the attribute was added to the set of connection attributes.

TRUNCATE TABLE is not permitted for the session_connect_attrs table.

24.10.10 Performance Schema User Variable Tables

As of MySQL 5.7.5, the Performance Schema provides a user_variables_by_thread table that exposes user-defined variables. These are variables defined within a specific session and include a @ character preceding the name; see Section 10.4, “User-Defined Variables”.

The user_variables_by_thread table contains these columns:

  • THREAD_ID

    The thread identifier of the session in which the variable is defined.

  • VARIABLE_NAME

    The variable name, without the leading @ character.

  • VARIABLE_VALUE

    The variable value.

TRUNCATE TABLE is not permitted for the user_variables_by_thread table.

24.10.11 Performance Schema Replication Tables

As of MySQL 5.7.2, the Performance Schema provides tables that expose replication information. This is similar to the information available from the SHOW SLAVE STATUS statement, but representation in table form is more accessible and has usability benefits:

  • SHOW SLAVE STATUS output is useful for visual inspection, but not so much for programmatic use. By contrast, using the Performance Schema tables, information about slave status can be searched using general SELECT queries, including complex WHERE conditions, joins, and so forth.

  • Query results can be saved in tables for further analysis, or assigned to variables and thus used in stored procedures.

  • The replication tables provide better diagnostic information. For multi-threaded slave operation, SHOW SLAVE STATUS reports all coordinator and worker thread errors using the Last_SQL_Errno and Last_SQL_Error fields, so only the most recent of those errors is visible and information can be lost. The replication tables store errors on a per-thread basis without loss of information.

  • The last seen transaction is visible in the replication tables on a per-worker basis. This is information not avilable from SHOW SLAVE STATUS.

  • Developers familiar with the Performance Schema interface can extend the replication tables to provide additional information by adding rows to the tables.

Replication Table Descriptions

The Performance Schema provides several replication-related tables:

  • Tables that contain information about the connection of the slave server to the master server:

  • Tables that contain general (not thread-specific) information about the transaction applier:

    • replication_applier_configuration: Configuration parameters for the transaction applier on the slave. Renamed from replication_execute_configuration in MySQL 5.7.6.

    • replication_applier_status: Current status of the transaction applier on the slave. Renamed from replication_execute_status in MySQL 5.7.6.

  • Tables that contain information about specific threads responsible for applying transactions received from the master:

  • Tables that contain information about replication group members:

The following sections describe each replication table in more detail, including the correspondence between the columns produced by SHOW SLAVE STATUS and the replication table columns in which the same information appears.

The remainder of this introduction to the replication tables describes how the Performance Schema populates them and which fields from SHOW SLAVE STATUS are not represented in the tables.

Replication Table Life Cycle

The Performance Schema populates the replication tables as follows:

  • Prior to execution of CHANGE MASTER TO, the tables are empty.

  • After CHANGE MASTER TO, the configuration parameters can be seen in the tables. At this time, there are no active slave threads, so the THREAD_ID columns are NULL and the SERVICE_STATE columns have a value of OFF.

  • After START SLAVE, non-NULL THREAD_ID values can be seen. Threads that are idle or active have a SERVICE_STATE value of ON. The thread that connects to the master server has a value of CONNECTING while it establishes the connection, and ON thereafter as long as the connection lasts.

  • After STOP SLAVE, the THREAD_ID columns become NULL and the SERVICE_STATE columns for threads that no longer exist have a value of OFF.

  • The tables are preserved after STOP SLAVE or threads dying due to an error.

  • The replication_applier_status_by_worker table is nonempty only when the slave is operating in multi-threaded mode. That is, if the slave_parallel_workers system variable is greater than 0, this table is populated when START SLAVE is executed, and the number of rows shows the number of workers.

SHOW SLAVE STATUS Information Not In the Replication Tables

The information in the Performance Schema replication tables differs somewhat from the information available from SHOW SLAVE STATUS because the tables are oriented toward use of global transaction identifiers (GTIDs), not file names and positions, and they represent server UUID values, not server ID values. Due to these differences, several SHOW SLAVE STATUS columns are not preserved in the Performance Schema replication tables, or are represented a different way:

  • The following fields refer to file names and positions and are not preserved:

    Master_Log_File
    Read_Master_Log_Pos
    Relay_Log_File
    Relay_Log_Pos
    Relay_Master_Log_File
    Exec_Master_Log_Pos
    Until_Condition
    Until_Log_File
    Until_Log_Pos
    
  • The Master_Info_File field is not preserved. It refers to the master.info file.

  • The following fields are based on server_id, not server_uuid, and are not preserved:

    Master_Server_Id
    Replicate_Ignore_Server_Ids
    
  • The Skip_Counter field is based on event counts, not GTIDs, and is not preserved.

  • These error fields are aliases for Last_SQL_Errno and Last_SQL_Error, so they are not preserved:

    Last_Errno
    Last_Error
    

    In the Performance Schema, this error information is available in the LAST_ERROR_NUMBER and LAST_ERROR_MESSAGE columns of the replication_applier_status_by_coordinator table (and replication_applier_status_by_worker if the slave is multi-threaded). Those tables provide more specific per-thread error information than is available from Last_Errno and Last_Error.

  • Fields that provide information about command-line filtering options is not preserved:

    Replicate_Do_DB
    Replicate_Ignore_DB
    Replicate_Do_Table
    Replicate_Ignore_Table
    Replicate_Wild_Do_Table
    Replicate_Wild_Ignore_Table
    
  • The Slave_IO_State and Slave_SQL_Running_State fields are not preserved. If needed, these values can be obtained from the process list by using the THREAD_ID column of the appropriate replication table and joining it with the ID column in the INFORMATION_SCHEMA PROCESSLIST table to select the STATE column of the latter table.

  • The Executed_Gtid_Set field can show a large set with a great deal of text. Instead, the Performance Schema tables show GTIDs of transactions that are currently being applied by the slave. Alternatively, the set of executed GTIDs can be obtained from the value of the gtid_executed system variable.

  • The Seconds_Behind_Master and Relay_Log_Space fields are in to-be-decided status and are not preserved.

Status Variables Moved to Replication Tables

As of MySQL version 5.7.5, the following status variables (previously monitored using SHOW STATUS) were moved to the Perfomance Schema replication tables:

These status variables are now only relevant when a single replication channel is being used because they only report the status of the default replication channel. When multiple replication channels exist, use the Performance Schema replication tables described in this section, which report these variables for each existing replication channel.

Replication Channels

The first column of the replication Performance Schema tables is CHANNEL_NAME. This enables the tables to be viewed per replication channel, added in MySQL 5.7.6. When you are using multiple replication channels on a slave, you can filter the tables per replication channel to monitor a specific replication channel. See Section 18.2.3, “Replication Channels” and Section 18.1.4.3, “Multi-Source Replication Monitoring” for more information.

24.10.11.1 The replication_connection_configuration Table

This table shows the configuration parameters used by the slave server for connecting to the master server. Parameters stored in the table can be changed at runtime with the CHANGE MASTER TO statement, as indicated in the column descriptions. This table was added in MySQL 5.7.2.

Compared to the replication_connection_status table, replication_connection_configuration changes less frequently. It contains values that define how the slave connects to the master and that remain constant during the connection, whereas replication_connection_status contains values that change during the connection.

The replication_connection_configuration table has these columns:

  • CHANNEL_NAME

    The replication channel which this row is displaying. There is always a default replication channel, and more replication channels can be added. See Section 18.2.3, “Replication Channels” for more information.

  • HOST

    The master host that the slave is connected to. (CHANGE MASTER TO option: MASTER_HOST)

  • PORT

    The port used to connect to the master. (CHANGE MASTER TO option: MASTER_PORT)

  • USER

    The user name of the account used to connect to the master. (CHANGE MASTER TO option: MASTER_USER)

  • NETWORK_INTERFACE

    The network interface that the slave is bound to, if any. (CHANGE MASTER TO option: MASTER_BIND)

  • AUTO_POSITION

    1 if autopositioning is in use; otherwise 0. (CHANGE MASTER TO option: MASTER_AUTO_POSITION)

  • SSL_ALLOWED, SSL_CA_FILE, SSL_CA_PATH, SSL_CERTIFICATE, SSL_CIPHER, SSL_KEY, SSL_VERIFY_SERVER_CERTIFICATE, SSL_CRL_FILE, SSL_CRL_PATH

    These columns show the SSL parameters used by the slave to connect to the master, if any.

    SSL_ALLOWED has these values:

    • Yes if an SSL connection to the master is permitted

    • No if an SSL connection to the master is not permitted

    • Ignored if an SSL connection is permitted but the slave server does not have SSL support enabled

    CHANGE MASTER TO options for the other SSL columns: MASTER_SSL_CA, MASTER_SSL_CAPATH, MASTER_SSL_CERT, MASTER_SSL_CIPHER, MASTER_SSL_CRL, MASTER_SSL_CRLPATH, MASTER_SSL_KEY, MASTER_SSL_VERIFY_SERVER_CERT.

    Prior to MySQL 5.7.4, the value of SSL_CRL_PATH was not displayed correctly. (Bug #18174719)

  • CONNECTION_RETRY_INTERVAL

    The number of seconds between connect retries. (CHANGE MASTER TO option: MASTER_CONNECT_RETRY)

  • CONNECTION_RETRY_COUNT

    The number of times the slave can attempt to reconnect to the master in the event of a lost connection. (CHANGE MASTER TO option: MASTER_RETRY_COUNT)

  • HEARTBEAT_INTERVAL

    The replication heartbeat interval on a slave, measured in seconds. Added in MySQL 5.7.5.

TRUNCATE TABLE is not permitted for the replication_connection_configuration table.

The following table shows the correspondence between replication_connection_configuration columns and SHOW SLAVE STATUS columns.

replication_connection_configuration ColumnSHOW SLAVE STATUS Column
HOSTMaster_Host
PORTMaster_Port
USERMaster_User
NETWORK_INTERFACEMaster_Bind
AUTO_POSITIONAuto_Position
SSL_ALLOWEDMaster_SSL_Allowed
SSL_CA_FILEMaster_SSL_CA_File
SSL_CA_PATHMaster_SSL_CA_Path
SSL_CERTIFICATEMaster_SSL_Cert
SSL_CIPHERMaster_SSL_Cipher
SSL_KEYMaster_SSL_Key
SSL_VERIFY_SERVER_CERTIFICATEMaster_SSL_Verify_Server_Cert
SSL_CRL_FILEMaster_SSL_Crl
SSL_CRL_PATHMaster_SSL_Crlpath
CONNECTION_RETRY_INTERVALConnect_Retry
CONNECTION_RETRY_COUNTMaster_Retry_Count

24.10.11.2 The replication_connection_status Table

As of MySQL 5.7.2, this table shows the current status of the I/O thread that handles the slave server connection to the master server.

Compared to the replication_connection_configuration table, replication_connection_status changes more frequently. It contains values that change during the connection, whereas replication_connection_configuration contains values which define how the slave connects to the master and that remain constant during the connection.

The replication_connection_status table has these columns:

  • CHANNEL_NAME

    The replication channel which this row is displaying. There is always a default replication channel, and more replication channels can be added. See Section 18.2.3, “Replication Channels” for more information.

  • GROUP_NAME

    If this server is a member of a group, shows the name of the group the server belongs to. Added in MySQL 5.7.6.

  • SOURCE_UUID

    The server_uuid value from the master.

  • THREAD_ID

    The I/O thread ID.

  • SERVICE_STATE

    ON (thread exists and is active or idle), OFF (thread no longer exists), or CONNECTING (thread exists and is connecting to the master).

  • RECEIVED_TRANSACTION_SET

    The set of global transaction IDs (GTIDs) corresponding to all transactions received by this slave. Empty if GTIDs are not in use. See GTID Sets for more information.

  • LAST_ERROR_NUMBER, LAST_ERROR_MESSAGE

    The error number and error message of the most recent error that caused the I/O thread to stop. An error number of 0 and message of the empty string mean no error. If the LAST_ERROR_MESSAGE value is not empty, the error values also appear in the slave's error log.

    Issuing RESET MASTER or RESET SLAVE resets the values shown in these columns.

  • LAST_ERROR_TIMESTAMP

    A timestamp in YYMMDD HH:MM:SS format that shows when the most recent I/O error took place.

  • LAST_HEARTBEAT_TIMESTAMP

    A timestamp in YYMMDD HH:MM:SS format that shows when the most recent heartbeat signal was received by a replication slave. Added in MySQL 5.7.5.

  • COUNT_RECEIVED_HEARTBEATS

    The total number of heartbeat signals that a replication slave received since the last time it was restarted or reset, or a CHANGE MASTER TO statement was issued. Added in MySQL 5.7.5.

TRUNCATE TABLE is not permitted for the replication_connection_status table.

The following table shows the correspondence between replication_connection_status columns and SHOW SLAVE STATUS columns.

replication_connection_status ColumnSHOW SLAVE STATUS Column
SOURCE_UUIDMaster_UUID
THREAD_IDNone
SERVICE_STATESlave_IO_Running
RECEIVED_TRANSACTION_SETRetrieved_Gtid_Set
LAST_ERROR_NUMBERLast_IO_Errno
LAST_ERROR_MESSAGELast_IO_Error
LAST_ERROR_TIMESTAMPLast_IO_Error_Timestamp

24.10.11.3 The replication_applier_configuration Table

This table shows the configuration parameters that affect transactions applied by the slave server. Parameters stored in the table can be changed at runtime with the CHANGE MASTER TO statement, as indicated in the column descriptions. This table was added in MySQL 5.7.2 with the name replication_execute_configuration, and renamed to replication_applier_configuration in MySQL 5.7.6.

The replication_applier_configuration table has these columns:

  • CHANNEL_NAME

    The replication channel which this row is displaying. There is always a default replication channel, and more replication channels can be added. See Section 18.2.3, “Replication Channels” for more information.

  • DESIRED_DELAY

    The number of seconds that the slave must lag the master. (CHANGE MASTER TO option: MASTER_DELAY)

TRUNCATE TABLE is not permitted for the replication_applier_configuration table.

The following table shows the correspondence between replication_applier_configuration columns and SHOW SLAVE STATUS columns.

replication_applier_configuration ColumnSHOW SLAVE STATUS Column
DESIRED_DELAYSQL_Delay

24.10.11.4 The replication_applier_status Table

This table shows the current general transaction execution status on the slave server. This table was added in MySQL 5.7.2 with the name replication_execute_status, and renamed to replication_applier_configuration in MySQL 5.7.6.

This table provides information about general aspects of transaction applier status that are not specific to any thread involved. Thread-specific status information is available in the replication_applier_status_by_coordinator table (and replication_applier_status_by_worker if the slave is multi-threaded).

The replication_applier_status table has these columns:

  • CHANNEL_NAME

    The replication channel which this row is displaying. There is always a default replication channel, and more replication channels can be added. See Section 18.2.3, “Replication Channels” for more information.

  • SERVICE_STATE

    Shows ON when the replication channel's applier threads are active or idle, OFF means that the applier threads are not active.

  • REMAINING_DELAY

    If the slave is waiting for DESIRED_DELAY seconds to pass since the master applied an event, this field contains the number of delay seconds remaining. At other times, this field is NULL. (The DESIRED_DELAY value is stored in the replication_applier_configuration table.)

  • COUNT_TRANSACTIONS_RETRIES

    Added in MySQL 5.7.5, shows the number of retries that were made because the slave SQL thread failed to apply a transaction.

TRUNCATE TABLE is not permitted for the replication_applier_status table.

The following table shows the correspondence between replication_applier_status columns and SHOW SLAVE STATUS columns.

replication_applier_status ColumnSHOW SLAVE STATUS Column
SERVICE_STATENone
REMAINING_DELAYSQL_Remaining_Delay

24.10.11.5 The replication_applier_status_by_coordinator Table

For a multi-threaded slave, the slave uses multiple worker threads and a coordinator thread to manage them, and this table shows the status of the coordinator thread. In MySQL 5.7.9 and later, for a single-threaded slave, this table is empty. (Previously, this table showed the applier thread status for a single-threaded slave; this information can now be found in the replication_applier_status_by_worker table in such cases. See Bug #74765, Bug #20001173.) This table was added in MySQL 5.7.2 as replication_execute_status_by_coordinator, and renamed replication_applier_status_by_coordinator in MySQL 5.7.6. For a multi-threaded slave, the replication_applier_status_by_worker table shows the status of the worker threads.

The replication_applier_status_by_coordinator table has these columns:

  • CHANNEL_NAME

    The replication channel which this row is displaying. There is always a default replication channel, and more replication channels can be added. See Section 18.2.3, “Replication Channels” for more information.

  • THREAD_ID

    The SQL/coordinator thread ID.

  • SERVICE_STATE

    ON (thread exists and is active or idle) or OFF (thread no longer exists).

  • LAST_ERROR_NUMBER, LAST_ERROR_MESSAGE

    The error number and error message of the most recent error that caused the SQL/coordinator thread to stop. An error number of 0 and message of the empty string mean no error. If the LAST_ERROR_MESSAGE value is not empty, the error values also appear in the slave's error log.

    Issuing RESET MASTER or RESET SLAVE resets the values shown in these columns.

    All error codes and messages displayed in the LAST_ERROR_NUMBER and LAST_ERROR_MESSAGE columns correspond to error values listed in Section B.3, “Server Error Codes and Messages”.

  • LAST_ERROR_TIMESTAMP

    A timestamp in YYMMDD HH:MM:SS format that shows when the most recent SQL/coordinator error occurred.

TRUNCATE TABLE is not permitted for the replication_applier_status_by_coordinator table.

The following table shows the correspondence between replication_applier_status_by_coordinator columns and SHOW SLAVE STATUS columns.

replication_applier_status_by_coordinator ColumnSHOW SLAVE STATUS Column
THREAD_IDNone
SERVICE_STATESlave_SQL_Running
LAST_ERROR_NUMBERLast_SQL_Errno
LAST_ERROR_MESSAGELast_SQL_Error
LAST_ERROR_TIMESTAMPLast_SQL_Error_Timestamp

24.10.11.6 The replication_applier_status_by_worker Table

In MySQL 5.7.9 and later, if the slave is not multi-threaded, this table shows the status of the applier thread. (Previously, this table was empty in such cases, and this information was reported in the replication_applier_status_by_coordinator table; see Bug #74765, Bug #20001173.) Otherwise, the slave uses multiple worker threads and a coordinator thread to manage them, and this table shows the status of the worker threads. This table was added in MySQL 5.7.2 as replication_execute_status_by_worker, and renamed replication_applier_status_by_worker in MySQL 5.7.6. For a multi-threaded slave, the replication_applier_status_by_coordinator table shows the status of the coordinator thread.

The replication_applier_status_by_worker table has these columns:

  • CHANNEL_NAME

    The replication channel which this row is displaying. There is always a default replication channel, and more replication channels can be added. See Section 18.2.3, “Replication Channels” for more information.

  • WORKER_ID

    The worker identifier (same value as the id column in the mysql.slave_worker_info table). After STOP SLAVE, the THREAD_ID column becomes NULL, but the WORKER_ID value is preserved.

  • THREAD_ID

    The worker thread identifier.

  • SERVICE_STATE

    ON (thread exists and is active or idle) or OFF (thread no longer exists).

  • LAST_SEEN_TRANSACTION

    The transaction that the worker has last seen. The worker has not necessarily applied this transaction because it could still be in the process of doing so.

    If the gtid_mode system variable value is OFF, this column is ANONYMOUS, indicating that transactions do not have global transaction identifiers (GTIDs) and are identified by file and position only.

    If gtid_mode is ON, the column value is defined as follows:

    • If no transaction has executed, the column is empty.

    • When a transaction has executed, the column is set from gtid_next as soon as gtid_next is set. From this moment, the column always shows a GTID.

    • The GTID is preserved until the next transaction is executed. If an error occurs, the column value is the GTID of the transaction being executed by the worker when the error occurred.

    • When the next GTID log event is picked up by this worker thread, this column is updated from gtid_next soon after gtid_next is set.

  • LAST_ERROR_NUMBER, LAST_ERROR_MESSAGE

    The error number and error message of the most recent error that caused the worker thread to stop. An error number of 0 and message of the empty string mean no error. If the LAST_ERROR_MESSAGE value is not empty, the error values also appear in the slave's error log.

    Issuing RESET MASTER or RESET SLAVE resets the values shown in these columns.

    All error codes and messages displayed in the LAST_ERROR_NUMBER and LAST_ERROR_MESSAGE columns correspond to error values listed in Section B.3, “Server Error Codes and Messages”.

  • LAST_ERROR_TIMESTAMP

    A timestamp in YYMMDD HH:MM:SS format that shows when the most recent worker error occurred.

TRUNCATE TABLE is not permitted for the replication_applier_status_by_worker table.

The following table shows the correspondence between replication_applier_status_by_worker columns and SHOW SLAVE STATUS columns.

replication_applier_status_by_worker ColumnSHOW SLAVE STATUS Column
WORKER_IDNone
THREAD_IDNone
SERVICE_STATENone
LAST_SEEN_TRANSACTIONNone
LAST_ERROR_NUMBERLast_SQL_Errno
LAST_ERROR_MESSAGELast_SQL_Error
LAST_ERROR_TIMESTAMPLast_SQL_Error_Timestamp

24.10.11.7 The replication_group_members Table

This table shows network and status information for replication group members. Added in MySQL 5.7.6.

The replication_group_members table has the following columns:

  • CHANNEL_NAME

    Name of the Group Replication channel.

  • MEMBER_ID

    Identifier for this member; same as the server UUID.

  • MEMBER_HOST

    Network address of this member (host name or IP address).

  • MEMBER_PORT

    Port on which the server is listening.

  • MEMBER_STATE

    Current state of this member; can be any one of the following:

    • OFFLINE: The Group Replication plugin is installed but has not been started.

    • RECOVERING: The server has joined a group from which it is retrieving data.

    • ONLINE: The member is in a fully functioning state.

TRUNCATE TABLE is not permitted for the replication_group_members table.

24.10.11.8 The replication_group_member_stats Table

This table shows statistical information for MySQL Group Replication members. It was added in MySQL 5.7.6 and is only populated when Group Replication is running.

The replication_group_member_stats table has the following columns:

  • CHANNEL_NAME

    Name of the Group Replication channel.

  • VIEW_ID

    Current view identifier for this group.

  • MEMBER_ID

    Identifier for this member; same as the server UUID.

  • COUNT_TRANSACTIONS_IN_QUEUE

    Number of transactions pending certification.

  • COUNT_TRANSACTIONS_CHECKED

    Number of transactions already certified by this member.

  • COUNT_CONFLICTS_DETECTED

    Number of transactions that were negatively certified.

  • COUNT_TRANSACTIONS_ROWS_VALIDATING

    Number of transaction rows available which could be used for certification, but which have not been garbage collected.

  • TRANSACTIONS_COMMITTED_ALL_MEMBERS

    Set of stable group transactions.

  • LAST_CONFLICT_FREE_TRANSACTION

    Latest transaction certified without conflicts.

TRUNCATE TABLE is not permitted for the replication_group_member_stats table.

24.10.12 Performance Schema Lock Tables

The Performance Schema exposes lock information through these tables:

The following sections describe these tables in more detail.

24.10.12.1 The metadata_locks Table

As of MySQL 5.7.3, the Performance Schema exposes metadata lock information through the metadata_locks table:

  • Locks that have been granted (shows which sessions own which current metadata locks)

  • Locks that have been requested but not yet granted (shows which sessions are waiting for which metadata locks).

  • Lock requests that have been killed by the deadlock detector or timed out and are waiting for the requesting session's lock request to be discarded

This information enables you to understand metadata lock dependencies between sessions. You can see not only which lock a session is waiting for, but which session currently holds that lock.

The metadata_locks table is read only and cannot be updated. It is autosized by default; to configure the table size, set the performance_schema_max_metadata_locks system variable at server startup.

Metadata lock instrumentation is disabled by default. To enable it, enable the wait/lock/metadata/sql/mdl instrument in the setup_instruments table.

The Performance Schema maintains metadata_locks table content as follows, using the LOCK_STATUS column to indicate the status of each lock:

  • When a metadata lock is requested and obtained immediately, a row with a status of GRANTED is inserted.

  • When a metadata lock is requested and not obtained immediately, a row with a status of PENDING is inserted.

  • When a metadata lock previously requested is granted, its row status is updated to GRANTED.

  • When a metadata lock is released, its row is deleted.

  • When a pending lock request is canceled by the deadlock detector to break a deadlock (ER_LOCK_DEADLOCK), its row status is updated from PENDING to VICTIM.

  • When a pending lock request times out (ER_LOCK_WAIT_TIMEOUT), its row status is updated from PENDING to TIMEOUT.

  • When granted lock or pending lock request is killed, its row status is updated from GRANTED or PENDING to KILLED.

  • The VICTIM, TIMEOUT, and KILLED status values are brief and signify that the lock row is about to be deleted.

  • The PRE_ACQUIRE_NOTIFY and POST_RELEASE_NOTIFY status values are brief and signify that the metadata locking subsubsystem is notifying interested storage engines while entering lock acquisition or leaving lock release operations. These status values were added in MySQL 5.7.11.

The metadata_locks table has these columns:

  • OBJECT_TYPE

    The type of lock used in the metadata lock subsystem: The value is one of GLOBAL, SCHEMA, TABLE, FUNCTION, PROCEDURE, TRIGGER (currently unused), EVENT, COMMIT, USER LEVEL LOCK, TABLESPACE, or LOCKING SERVICE.

    A value of USER LEVEL LOCK indicates a lock acquired with GET_LOCK(). A value of LOCKING SERVICE indicates a lock acquired using the locking service described in Section 27.3.1, “The Locking Service”.

  • OBJECT_SCHEMA

    The schema that contains the object.

  • OBJECT_NAME

    The name of the instrumented object.

  • OBJECT_INSTANCE_BEGIN

    The address in memory of the instrumented object.

  • LOCK_TYPE

    The lock type from the metadata lock subsystem. The value is one of INTENTION_EXCLUSIVE, SHARED, SHARED_HIGH_PRIO, SHARED_READ, SHARED_WRITE, SHARED_UPGRADABLE, SHARED_NO_WRITE, SHARED_NO_READ_WRITE, or EXCLUSIVE.

  • LOCK_DURATION

    The lock duration from the metadata lock subsystem. The value is one of STATEMENT, TRANSACTION, or EXPLICIT. The STATEMENT and TRANSACTION values are for locks that are released at statement or transaction end, respectively. The EXPLICIT value is for locks that survive statement or transaction end and are released explicitly, such as global locks acquired with FLUSH TABLES WITH READ LOCK.

  • LOCK_STATUS

    The lock status from the metadata lock subsystem. The value is one of PENDING, GRANTED, VICTIM, TIMEOUT, KILLED, PRE_ACQUIRE_NOTIFY, or POST_RELEASE_NOTIFY. The Performance Schema assigns these values as described earlier in this section.

  • SOURCE

    The name of the source file containing the instrumented code that produced the event and the line number in the file at which the instrumentation occurs. This enables you to check the source to determine exactly what code is involved.

  • OWNER_THREAD_ID

    The thread requesting a metadata lock.

  • OWNER_EVENT_ID

    The event requesting a metadata lock.

TRUNCATE TABLE is not permitted for the metadata_locks table.

24.10.12.2 The table_handles Table

As of MySQL 5.7.3, the Performance Schema exposes table lock information through the table_handles table to show the table locks currently in effect for each opened table handle. table_handles reports what is recorded by the table lock instrumentation. This information shows which table handles the server has open, how they are locked, and by which sessions.

The table_handles table is read only and cannot be updated. It is autosized by default; to configure the table size, set the performance_schema_max_table_handles system variable at server startup.

The table_handles table has these columns:

  • OBJECT_TYPE

    The table opened by a table handle.

  • OBJECT_SCHEMA

    The schema that contains the object.

  • OBJECT_NAME

    The name of the instrumented object.

  • OBJECT_INSTANCE_BEGIN

    The table handle address in memory.

  • OWNER_THREAD_ID

    The thread owning the table handle.

  • OWNER_EVENT_ID

    The event which caused the table handle to be opened.

  • INTERNAL_LOCK

    The table lock used at the SQL level. The value is one of READ, READ WITH SHARED LOCKS, READ HIGH PRIORITY, READ NO INSERT, WRITE ALLOW WRITE, WRITE CONCURRENT INSERT, WRITE LOW PRIORITY, or WRITE. For information about these lock types, see the include/thr_lock.h source file.

  • EXTERNAL_LOCK

    The table lock used at the storage engine level. The value is one of READ EXTERNAL or WRITE EXTERNAL.

TRUNCATE TABLE is not permitted for the table_handles table.

24.10.13 Performance Schema System Variable Tables

Note

The value of the show_compatibility_56 system variable affects the information available from the tables described here. For details, see the description of that variable in Section 6.1.5, “Server System Variables”.

The MySQL server maintains many system variables that indicate how it is configured (see Section 6.1.5, “Server System Variables”). As of MySQL 5.7.6, system variable information is available in these Performance Schema tables:

  • global_variables: Global system variables. An application that wants only global values should use this table.

  • session_variables: System variables for the current session. An application that wants all system variable values for its own session should use this table. It includes the session variables for its session, as well as the values of global variables that have no session counterpart. (In MySQL 5.7.6 and 5.7.7, the table does not fully reflect all system variable values in effect for the current session; it includes no rows for global variables that have no session counterpart. This is corrected in MySQL 5.7.8.)

  • variables_by_thread: Session system variables for each active session. An application that wants to know the session variable values for specific sessions should use this table. It includes session variables only, identified by thread ID.

The session variable tables (session_variables, variables_by_thread) contain information only for active sessions, not terminated sessions.

TRUNCATE TABLE is not supported for Performance Schema system variable tables.

The global_variables and session_variables tables have these columns:

  • VARIABLE_NAME

    The system variable name.

  • VARIABLE_VALUE

    The system variable value. For global_variables, this column contains the global value. For session_variables, this column contains the variable value in effect for the current session.

The variables_by_thread table has these columns:

  • THREAD_ID

    The thread identifier of the session in which the system variable is defined.

  • VARIABLE_NAME

    The system variable name.

  • VARIABLE_VALUE

    The session variable value for the session named by the THREAD_ID column.

The variables_by_thread table contains system variable information only about foreground threads. If not all threads are instrumented by the Performance Schema, this table will miss some rows. In this case, the Performance_schema_thread_instances_lost status variable will be greater than zero.

24.10.14 Performance Schema Status Variable Tables

Note

The value of the show_compatibility_56 system variable affects the information available from the tables described here. For details, see the description of that variable in Section 6.1.5, “Server System Variables”.

The MySQL server maintains many status variables that provide information about its operation (see Section 6.1.7, “Server Status Variables”). As of MySQL 5.7.6, status variable information is available in these Performance Schema tables:

  • global_status: Global status variables. An application that wants only global values should use this table.

  • session_status: Status variables for the current session. An application that wants all status variable values for its own session should use this table. It includes the session variables for its session, as well as the values of global variables that have no session counterpart. (In MySQL 5.7.6 and 5.7.7, the table does not fully reflect all status variable values in effect for the current session; it includes no rows for global variables that have no session counterpart. This is corrected in MySQL 5.7.8.)

  • status_by_thread: Session status variables for each active session. An application that wants to know the session variable values for specific sessions should use this table. It includes session variables only, identified by thread ID.

There are also summary tables that provide status variable information aggregated by account, host name, and user name. See Section 24.10.15.10, “Status Variable Summary Tables”.

The session variable tables (session_status, status_by_thread) contain information only for active sessions, not terminated sessions.

The Performance Schema collects statistics for global status variables only for threads for which the INSTRUMENTED value is YES in the threads table. Statistics for session status variables are always collected, regardless of the INSTRUMENTED value.

The Performance Schema does not collect statistics for Com_xxx status variables in the status variable tables. To obtain global and per-session statement execution counts, use the events_statements_summary_global_by_event_name and events_statements_summary_by_thread_by_event_name tables, respectively. For example:

SELECT EVENT_NAME, COUNT_STAR
FROM events_statements_summary_global_by_event_name
WHERE EVENT_NAME LIKE 'statement/sql/%';

The global_status and session_status tables have these columns:

  • VARIABLE_NAME

    The status variable name.

  • VARIABLE_VALUE

    The status variable value. For global_status, this column contains the global value. For session_status, this column contains the variable value for the current session.

The status_by_thread table contains the status of each active thread. It has these columns:

  • THREAD_ID

    The thread identifier of the session in which the status variable is defined.

  • VARIABLE_NAME

    The status variable name.

  • VARIABLE_VALUE

    The session variable value for the session named by the THREAD_ID column.

The status_by_thread table contains status variable information only about foreground threads. If the performance_schema_max_thread_instances system variable is not autoscaled (set to −1) and the maximum permitted number of instrumented thread objects is not greater than the number of background threads, the table will be empty.

The Performance Schema supports TRUNCATE TABLE for status variable tables as follows:

FLUSH STATUS adds the session status from all active sessions to the global status variables, resets the status of all active sessions, and resets account, host, and user status values aggregated from disconnected sessions.

24.10.15 Performance Schema Summary Tables

Summary tables provide aggregated information for terminated events over time. The tables in this group summarize event data in different ways.

Wait Event Summaries:

Stage Summaries:

Statement Summaries:

Transaction Summaries:

Object Wait Summaries:

File I/O Summaries:

Table I/O and Lock Wait Summaries:

Socket Summaries:

Memory Summaries:

Status Variable Summaries:

  • status_by_account: Status variables summarized by account (added in MySQL 5.7.6)

  • status_by_host: Status variables summarized by host name (added in MySQL 5.7.6)

  • status_by_user: Status variables summarized by user name (added in MySQL 5.7.6)

Each summary table has grouping columns that determine how to group the data to be aggregated, and summary columns that contain the aggregated values. Tables that summarize events in similar ways often have similar sets of summary columns and differ only in the grouping columns used to determine how events are aggregated.

Summary tables can be truncated with TRUNCATE TABLE. Generally, the effect is to reset the summary columns to 0 or NULL, not to remove rows. This enables you to clear collected values and restart aggregation. That might be useful, for example, after you have made a runtime configuration change. Exceptions to this truncation behavior are noted in individual summary table sections.

24.10.15.1 Wait Event Summary Tables

The Performance Schema maintains tables for collecting current and recent wait events, and aggregates that information in summary tables. Section 24.10.4, “Performance Schema Wait Event Tables” describes the events on which wait summaries are based. See that discussion for information about the content of wait events, the current and recent wait event tables, and how to control wait event collection, which is disabled by default.

Example wait event summary information:

mysql> SELECT * FROM events_waits_summary_global_by_event_name\G
...
*************************** 6. row ***************************
    EVENT_NAME: wait/synch/mutex/sql/BINARY_LOG::LOCK_index
    COUNT_STAR: 8
SUM_TIMER_WAIT: 2119302
MIN_TIMER_WAIT: 196092
AVG_TIMER_WAIT: 264912
MAX_TIMER_WAIT: 569421
...
*************************** 9. row ***************************
    EVENT_NAME: wait/synch/mutex/sql/hash_filo::lock
    COUNT_STAR: 69
SUM_TIMER_WAIT: 16848828
MIN_TIMER_WAIT: 0
AVG_TIMER_WAIT: 244185
MAX_TIMER_WAIT: 735345
...

Each wait event summary table has one or more grouping columns to indicate how the table aggregates events. Event names refer to names of event instruments in the setup_instruments table.

  • events_waits_summary_by_account_by_event_name has EVENT_NAME, USER, and HOST columns. Each row summarizes events for a given account (user and host combination) and event name.

  • events_waits_summary_by_host_by_event_name has EVENT_NAME and HOST columns. Each row summarizes events for a given host and event name.

  • events_waits_summary_by_instance has EVENT_NAME and OBJECT_INSTANCE_BEGIN columns. Each row summarizes events for a given event name and object. If an instrument is used to create multiple instances, each instance has a unique OBJECT_INSTANCE_BEGIN value and is summarized separately in this table.

  • events_waits_summary_by_thread_by_event_name has THREAD_ID and EVENT_NAME columns. Each row summarizes events for a given thread and event name.

  • events_waits_summary_by_user_by_event_name has EVENT_NAME and USER columns. Each row summarizes events for a given user and event name.

  • events_waits_summary_global_by_event_name has an EVENT_NAME column. Each row summarizes events for a given event name. An instrument might be used to create multiple instances of the instrumented object. For example, if there is an instrument for a mutex that is created for each connection, there are as many instances as there are connections. The summary row for the instrument summarizes over all these instances.

Each wait event summary table has these summary columns containing aggregated values:

  • COUNT_STAR

    The number of summarized events. This value includes all events, whether timed or nontimed.

  • SUM_TIMER_WAIT

    The total wait time of the summarized timed events. This value is calculated only for timed events because nontimed events have a wait time of NULL. The same is true for the other xxx_TIMER_WAIT values.

  • MIN_TIMER_WAIT

    The minimum wait time of the summarized timed events.

  • AVG_TIMER_WAIT

    The average wait time of the summarized timed events.

  • MAX_TIMER_WAIT

    The maximum wait time of the summarized timed events.

TRUNCATE TABLE is permitted for wait summary tables. It has these effects:

  • For summary tables not aggregated by account, host, or user, truncation resets the summary columns to zero rather than removing rows.

  • For summary tables aggregated by account, host, or user, truncation removes rows for accounts, hosts, or users with no connections, and resets the summary columns to zero for the remaining rows.

In addition, each wait summary table that is aggregated by account, host, user, or thread is implicitly truncated by truncation of the connection table on which it depends, or truncation of events_waits_summary_global_by_event_name. For details, see Section 24.10.8, “Performance Schema Connection Tables”.

24.10.15.2 Stage Summary Tables

The Performance Schema maintains tables for collecting current and recent stage events, and aggregates that information in summary tables. Section 24.10.5, “Performance Schema Stage Event Tables” describes the events on which stage summaries are based. See that discussion for information about the content of stage events, the current and recent stage event tables, and how to control stage event collection, which is disabled by default.

Example stage event summary information:

mysql> SELECT * FROM events_stages_summary_global_by_event_name\G
...
*************************** 5. row ***************************
    EVENT_NAME: stage/sql/checking permissions
    COUNT_STAR: 57
SUM_TIMER_WAIT: 26501888880
MIN_TIMER_WAIT: 7317456
AVG_TIMER_WAIT: 464945295
MAX_TIMER_WAIT: 12858936792
...
*************************** 9. row ***************************
    EVENT_NAME: stage/sql/closing tables
    COUNT_STAR: 37
SUM_TIMER_WAIT: 662606568
MIN_TIMER_WAIT: 1593864
AVG_TIMER_WAIT: 17907891
MAX_TIMER_WAIT: 437977248
...

Each stage summary table has one or more grouping columns to indicate how the table aggregates events. Event names refer to names of event instruments in the setup_instruments table.

Each stage summary table has these summary columns containing aggregated values: COUNT_STAR, SUM_TIMER_WAIT, MIN_TIMER_WAIT, AVG_TIMER_WAIT, and MAX_TIMER_WAIT. These columns are analogous to the columns of the same names in the wait event summary tables (see Section 24.10.15.1, “Wait Event Summary Tables”), except that the stage summary tables aggregate events from events_stages_current rather than events_waits_current.

TRUNCATE TABLE is permitted for stage summary tables. It has these effects:

  • For summary tables not aggregated by account, host, or user, truncation resets the summary columns to zero rather than removing rows.

  • For summary tables aggregated by account, host, or user, truncation removes rows for accounts, hosts, or users with no connections, and resets the summary columns to zero for the remaining rows.

In addition, each stage summary table that is aggregated by account, host, user, or thread is implicitly truncated by truncation of the connection table on which it depends, or truncation of events_stages_summary_global_by_event_name. For details, see Section 24.10.8, “Performance Schema Connection Tables”.

24.10.15.3 Statement Summary Tables

The Performance Schema maintains tables for collecting current and recent statement events, and aggregates that information in summary tables. Section 24.10.6, “Performance Schema Statement Event Tables” describes the events on which statement summaries are based. See that discussion for information about the content of statement events, the current and recent statement event tables, and how to control statement event collection, which is partially disabled by default.

Example statement event summary information:

mysql> SELECT * FROM events_statements_summary_global_by_event_name\G
*************************** 1. row ***************************
                 EVENT_NAME: statement/sql/select
                 COUNT_STAR: 25
             SUM_TIMER_WAIT: 1535983999000
             MIN_TIMER_WAIT: 209823000
             AVG_TIMER_WAIT: 61439359000
             MAX_TIMER_WAIT: 1363397650000
              SUM_LOCK_TIME: 20186000000
                 SUM_ERRORS: 0
               SUM_WARNINGS: 0
          SUM_ROWS_AFFECTED: 0
              SUM_ROWS_SENT: 388
          SUM_ROWS_EXAMINED: 370
SUM_CREATED_TMP_DISK_TABLES: 0
     SUM_CREATED_TMP_TABLES: 0
       SUM_SELECT_FULL_JOIN: 0
 SUM_SELECT_FULL_RANGE_JOIN: 0
           SUM_SELECT_RANGE: 0
     SUM_SELECT_RANGE_CHECK: 0
            SUM_SELECT_SCAN: 6
      SUM_SORT_MERGE_PASSES: 0
             SUM_SORT_RANGE: 0
              SUM_SORT_ROWS: 0
              SUM_SORT_SCAN: 0
          SUM_NO_INDEX_USED: 6
     SUM_NO_GOOD_INDEX_USED: 0
...

Each statement summary table has one or more grouping columns to indicate how the table aggregates events. Event names refer to names of event instruments in the setup_instruments table.

Each statement summary table has these summary columns containing aggregated values (with exceptions as noted):

The events_statements_summary_by_digest table has these additional summary columns:

  • FIRST_SEEN_TIMESTAMP, LAST_SEEN_TIMESTAMP

    The times at which a statement with the given digest value were first seen and most recently seen.

The events_statements_summary_by_program table has these additional summary columns:

  • COUNT_STATEMENTS, SUM_STATEMENTS_WAIT, MIN_STATEMENTS_WAIT, AVG_STATEMENTS_WAIT, MAX_STATEMENTS_WAIT

    Statistics about nested statements invoked during stored program execution.

The prepared_statements_instances table has these additional summary columns:

  • COUNT_EXECUTE, SUM_TIMER_EXECUTE, MIN_TIMER_EXECUTE, AVG_TIMER_EXECUTE, MAX_TIMER_EXECUTE

    Aggregated statistics for executions of the prepared statement.

TRUNCATE TABLE is permitted for statement summary tables. It has these effects:

  • For events_statements_summary_by_digest, it removes the rows.

  • For other summary tables not aggregated by account, host, or user, truncation resets the summary columns to zero rather than removing rows.

  • For other summary tables aggregated by account, host, or user, truncation removes rows for accounts, hosts, or users with no connections, and resets the summary columns to zero for the remaining rows.

In addition, each statement summary table that is aggregated by account, host, user, or thread is implicitly truncated by truncation of the connection table on which it depends, or truncation of events_statements_summary_global_by_event_name. For details, see Section 24.10.8, “Performance Schema Connection Tables”.

Statement Digest Aggregation Rules

If the statement_digest consumer is enabled, aggregation into events_statements_summary_by_digest occurs as follows when a statement completes. Aggregation is based on the DIGEST value computed for the statement.

  • If a events_statements_summary_by_digest row already exists with the digest value for the statement that just completed, statistics for the statement are aggregated to that row. The LAST_SEEN column is updated to the current time.

  • If no row has the digest value for the statement that just completed, and the table is not full, a new row is created for the statement. The FIRST_SEEN and LAST_SEEN columns are initialized with the current time.

  • If no row has the statement digest value for the statement that just completed, and the table is full, the statistics for the statement that just completed are added to a special catch-all row with DIGEST = NULL, which is created if necessary. If the row is created, the FIRST_SEEN and LAST_SEEN columns are initialized with the current time. Otherwise, the LAST_SEEN column is updated with the current time.

The row with DIGEST = NULL is maintained because Performance Schema tables have a maximum size due to memory constraints. The DIGEST = NULL row permits digests that do not match other rows to be counted even if the summary table is full, using a common other bucket. This row helps you estimate whether the digest summary is representative:

  • A DIGEST = NULL row that has a COUNT_STAR value that represents 5% of all digests shows that the digest summary table is very representative; the other rows cover 95% of the statements seen.

  • A DIGEST = NULL row that has a COUNT_STAR value that represents 50% of all digests shows that the digest summary table is not very representative; the other rows cover only half the statements seen. Most likely the DBA should increase the maximum table size so that more of the rows counted in the DIGEST = NULL row would be counted using more specific rows instead. To do this, set the performance_schema_digests_size system variable to a larger value at server startup. The default size is 200.

Stored Program Instrumentation Behavior

For stored program types for which instrumentation is enabled in the setup_objects table, events_statements_summary_by_program maintains statistics for stored programs as follows:

  • A row is added for an object when it is first used in the server.

  • The row for an object is removed when the object is dropped.

  • Statistics are aggregated in the row for an object as it executes.

See also Section 24.3.3, “Event Pre-Filtering”.

24.10.15.4 Transaction Summary Tables

As of MySQL 5.7.3, the Performance Schema maintains tables for collecting current and recent transaction events, and aggregates that information in summary tables. Section 24.10.7, “Performance Schema Transaction Tables” describes the events on which transaction summaries are based. See that discussion for information about the content of transaction events, the current and recent transaction event tables, and how to control transaction event collection, which is disabled by default.

Example transaction event summary information:

mysql> SELECT * FROM events_transactions_summary_global_by_event_name LIMIT 1\G
*************************** 1. row ***************************
          EVENT_NAME: transaction
          COUNT_STAR: 5
      SUM_TIMER_WAIT: 19550092000
      MIN_TIMER_WAIT: 2954148000
      AVG_TIMER_WAIT: 3910018000
      MAX_TIMER_WAIT: 5486275000
    COUNT_READ_WRITE: 5
SUM_TIMER_READ_WRITE: 19550092000
MIN_TIMER_READ_WRITE: 2954148000
AVG_TIMER_READ_WRITE: 3910018000
MAX_TIMER_READ_WRITE: 5486275000
     COUNT_READ_ONLY: 0
 SUM_TIMER_READ_ONLY: 0
 MIN_TIMER_READ_ONLY: 0
 AVG_TIMER_READ_ONLY: 0
 MAX_TIMER_READ_ONLY: 0

Each transaction summary table has one or more grouping columns to indicate how the table aggregates events. Event names refer to names of event instruments in the setup_instruments table.

Each transaction summary table has these summary columns containing aggregated values:

  • COUNT_STAR, SUM_TIMER_WAIT, MIN_TIMER_WAIT, AVG_TIMER_WAIT, MAX_TIMER_WAIT

    These columns are analogous to the columns of the same names in the wait event summary tables (see Section 24.10.15.1, “Wait Event Summary Tables”), except that the transaction summary tables aggregate events from events_transactions_current rather than events_waits_current. These columns summarize read-write and read-only transactions.

  • COUNT_READ_WRITE, SUM_TIMER_READ_WRITE, MIN_TIMER_READ_WRITE, AVG_TIMER_READ_WRITE, MAX_TIMER_READ_WRITE

    These are similar to the COUNT_STAR and xxx_TIMER_WAIT columns, but summarize read-write transactions only.

  • COUNT_READ_ONLY, SUM_TIMER_READ_ONLY, MIN_TIMER_READ_ONLY, AVG_TIMER_READ_ONLY, MAX_TIMER_READ_ONLY

    These are similar to the COUNT_STAR and xxx_TIMER_WAIT columns, but summarize read-only transactions only.

TRUNCATE TABLE is permitted for transaction summary tables. It has these effects:

  • For summary tables not aggregated by account, host, or user, truncation resets the summary columns to zero rather than removing rows.

  • For summary tables aggregated by account, host, or user, truncation removes rows for accounts, hosts, or users with no connections, and resets the summary columns to zero for the remaining rows.

In addition, each transaction summary table that is aggregated by account, host, user, or thread is implicitly truncated by truncation of the connection table on which it depends, or truncation of events_transactions_summary_global_by_event_name. For details, see Section 24.10.8, “Performance Schema Connection Tables”.

Transaction Aggregation Rules

Transaction event collection occurs without regard to isolation level, access mode, or autocommit mode.

Read-write transactions are generally more resource intensive than read-only transactions, therefore transaction summary tables include separate aggregate columns for read-write and read-only transactions.

Resource requirements may also vary with transaction isolation level. However, presuming that only one isolation level would be used per server, aggregation by isolation level is not provided.

24.10.15.5 Object Wait Summary Table

The Performance Schema maintains the objects_summary_global_by_type table for aggregating object wait events.

Example object wait event summary information:

mysql> SELECT * FROM objects_summary_global_by_type\G
...
*************************** 3. row ***************************
   OBJECT_TYPE: TABLE
 OBJECT_SCHEMA: test
   OBJECT_NAME: t
    COUNT_STAR: 3
SUM_TIMER_WAIT: 263126976
MIN_TIMER_WAIT: 1522272
AVG_TIMER_WAIT: 87708678
MAX_TIMER_WAIT: 258428280
...
*************************** 10. row ***************************
   OBJECT_TYPE: TABLE
 OBJECT_SCHEMA: mysql
   OBJECT_NAME: user
    COUNT_STAR: 14
SUM_TIMER_WAIT: 365567592
MIN_TIMER_WAIT: 1141704
AVG_TIMER_WAIT: 26111769
MAX_TIMER_WAIT: 334783032
...

The objects_summary_global_by_type table has these grouping columns to indicate how the table aggregates events: OBJECT_TYPE, OBJECT_SCHEMA, and OBJECT_NAME. Each row summarizes events for the given object.

objects_summary_global_by_type has the same summary columns as the events_waits_summary_by_xxx tables. See Section 24.10.15.1, “Wait Event Summary Tables”.

TRUNCATE TABLE is permitted for the object summary table. It resets the summary columns to zero rather than removing rows.

24.10.15.6 File I/O Summary Tables

The Performance Schema maintains file I/O summary tables that aggregate information about I/O operations.

Example file I/O event summary information:

mysql> SELECT * FROM file_summary_by_event_name\G
...
*************************** 2. row ***************************
               EVENT_NAME: wait/io/file/sql/binlog
               COUNT_STAR: 31
           SUM_TIMER_WAIT: 8243784888
           MIN_TIMER_WAIT: 0
           AVG_TIMER_WAIT: 265928484
           MAX_TIMER_WAIT: 6490658832
...
mysql> SELECT * FROM file_summary_by_instance\G
...
*************************** 2. row ***************************
                FILE_NAME: /var/mysql/share/english/errmsg.sys
               EVENT_NAME: wait/io/file/sql/ERRMSG
               EVENT_NAME: wait/io/file/sql/ERRMSG
    OBJECT_INSTANCE_BEGIN: 4686193384
               COUNT_STAR: 5
           SUM_TIMER_WAIT: 13990154448
           MIN_TIMER_WAIT: 26349624
           AVG_TIMER_WAIT: 2798030607
           MAX_TIMER_WAIT: 8150662536
...

Each file I/O summary table has one or more grouping columns to indicate how the table aggregates events. Event names refer to names of event instruments in the setup_instruments table.

  • file_summary_by_event_name has an EVENT_NAME column. Each row summarizes events for a given event name.

  • file_summary_by_instance has FILE_NAME, EVENT_NAME, and OBJECT_INSTANCE_BEGIN columns. Each row summarizes events for a given file and event name.

Each file I/O summary table has the following summary columns containing aggregated values. Some columns are more general and have values that are the same as the sum of the values of more fine-grained columns. In this way, aggregations at higher levels are available directly without the need for user-defined views that sum lower-level columns.

  • COUNT_STAR, SUM_TIMER_WAIT, MIN_TIMER_WAIT, AVG_TIMER_WAIT, MAX_TIMER_WAIT

    These columns aggregate all I/O operations.

  • COUNT_READ, SUM_TIMER_READ, MIN_TIMER_READ, AVG_TIMER_READ, MAX_TIMER_READ, SUM_NUMBER_OF_BYTES_READ

    These columns aggregate all read operations, including FGETS, FGETC, FREAD, and READ.

  • COUNT_WRITE, SUM_TIMER_WRITE, MIN_TIMER_WRITE, AVG_TIMER_WRITE, MAX_TIMER_WRITE, SUM_NUMBER_OF_BYTES_WRITE

    These columns aggregate all write operations, including FPUTS, FPUTC, FPRINTF, VFPRINTF, FWRITE, and PWRITE.

  • COUNT_MISC, SUM_TIMER_MISC, MIN_TIMER_MISC, AVG_TIMER_MISC, MAX_TIMER_MISC

    These columns aggregate all other I/O operations, including CREATE, DELETE, OPEN, CLOSE, STREAM_OPEN, STREAM_CLOSE, SEEK, TELL, FLUSH, STAT, FSTAT, CHSIZE, RENAME, and SYNC. There are no byte counts for these operations.

TRUNCATE TABLE is permitted for file I/O summary tables. It resets the summary columns to zero rather than removing rows.

The MySQL server uses several techniques to avoid I/O operations by caching information read from files, so it is possible that statements you might expect to result in I/O events will not. You may be able to ensure that I/O does occur by flushing caches or restarting the server to reset its state.

24.10.15.7 Table I/O and Lock Wait Summary Tables

The following sections describe the table I/O and lock wait summary tables:

24.10.15.7.1 The table_io_waits_summary_by_table Table

The table_io_waits_summary_by_table table aggregates all table I/O wait events, as generated by the wait/io/table/sql/handler instrument. The grouping is by table.

The table_io_waits_summary_by_table table has these grouping columns to indicate how the table aggregates events: OBJECT_TYPE, OBJECT_SCHEMA, and OBJECT_NAME. These columns have the same meaning as in the events_waits_current table. They identify the table to which the row applies.

table_io_waits_summary_by_table has the following summary columns containing aggregated values. As indicated in the column descriptions, some columns are more general and have values that are the same as the sum of the values of more fine-grained columns. For example, columns that aggregate all writes hold the sum of the corresponding columns that aggregate inserts, updates, and deletes. In this way, aggregations at higher levels are available directly without the need for user-defined views that sum lower-level columns.

  • COUNT_STAR, SUM_TIMER_WAIT, MIN_TIMER_WAIT, AVG_TIMER_WAIT, MAX_TIMER_WAIT

    These columns aggregate all I/O operations. They are the same as the sum of the corresponding xxx_READ and xxx_WRITE columns.

  • COUNT_READ, SUM_TIMER_READ, MIN_TIMER_READ, AVG_TIMER_READ, MAX_TIMER_READ

    These columns aggregate all read operations. They are the same as the sum of the corresponding xxx_FETCH columns.

  • COUNT_WRITE, SUM_TIMER_WRITE, MIN_TIMER_WRITE, AVG_TIMER_WRITE, MAX_TIMER_WRITE

    These columns aggregate all write operations. They are the same as the sum of the corresponding xxx_INSERT, xxx_UPDATE, and xxx_DELETE columns.

  • COUNT_FETCH, SUM_TIMER_FETCH, MIN_TIMER_FETCH, AVG_TIMER_FETCH, MAX_TIMER_FETCH

    These columns aggregate all fetch operations.

  • COUNT_INSERT, SUM_TIMER_INSERT, MIN_TIMER_INSERT, AVG_TIMER_INSERT, MAX_TIMER_INSERT

    These columns aggregate all insert operations.

  • COUNT_UPDATE, SUM_TIMER_UPDATE, MIN_TIMER_UPDATE, AVG_TIMER_UPDATE, MAX_TIMER_UPDATE

    These columns aggregate all update operations.

  • COUNT_DELETE, SUM_TIMER_DELETE, MIN_TIMER_DELETE, AVG_TIMER_DELETE, MAX_TIMER_DELETE

    These columns aggregate all delete operations.

TRUNCATE TABLE is permitted for table I/O summary tables. It resets the summary columns to zero rather than removing rows. Truncating this table also truncates the table_io_waits_summary_by_index_usage table.

24.10.15.7.2 The table_io_waits_summary_by_index_usage Table

The table_io_waits_summary_by_index_usage table aggregates all table index I/O wait events, as generated by the wait/io/table/sql/handler instrument. The grouping is by table index.

The columns of table_io_waits_summary_by_index_usage are nearly identical to table_io_waits_summary_by_table. The only difference is the additional group column, INDEX_NAME, which corresponds to the name of the index that was used when the table I/O wait event was recorded:

  • A value of PRIMARY indicates that table I/O used the primary index.

  • A value of NULL means that table I/O used no index.

  • Inserts are counted against INDEX_NAME = NULL.

TRUNCATE TABLE is permitted for table I/O summary tables. It resets the summary columns to zero rather than removing rows. This table is also truncated by truncation of the table_io_waits_summary_by_table table. A DDL operation that changes the index structure of a table may cause the per-index statistics to be reset.

24.10.15.7.3 The table_lock_waits_summary_by_table Table

The table_lock_waits_summary_by_table table aggregates all table lock wait events, as generated by the wait/lock/table/sql/handler instrument. The grouping is by table.

This table contains information about internal and external locks:

  • An internal lock corresponds to a lock in the SQL layer. This is currently implemented by a call to thr_lock(). In event rows, these locks are distinguished by the OPERATION column, which has one of these values:

    read normal
    read with shared locks
    read high priority
    read no insert
    write allow write
    write concurrent insert
    write delayed
    write low priority
    write normal
    
  • An external lock corresponds to a lock in the storage engine layer. This is currently implemented by a call to handler::external_lock(). In event rows, these locks are distinguished by the OPERATION column, which has one of these values:

    read external
    write external
    

The table_lock_waits_summary_by_table table has these grouping columns to indicate how the table aggregates events: OBJECT_TYPE, OBJECT_SCHEMA, and OBJECT_NAME. These columns have the same meaning as in the events_waits_current table. They identify the table to which the row applies.

table_lock_waits_summary_by_table has the following summary columns containing aggregated values. As indicated in the column descriptions, some columns are more general and have values that are the same as the sum of the values of more fine-grained columns. For example, columns that aggregate all locks hold the sum of the corresponding columns that aggregate read and write locks. In this way, aggregations at higher levels are available directly without the need for user-defined views that sum lower-level columns.

  • COUNT_STAR, SUM_TIMER_WAIT, MIN_TIMER_WAIT, AVG_TIMER_WAIT, MAX_TIMER_WAIT

    These columns aggregate all lock operations. They are the same as the sum of the corresponding xxx_READ and xxx_WRITE columns.

  • COUNT_READ, SUM_TIMER_READ, MIN_TIMER_READ, AVG_TIMER_READ, MAX_TIMER_READ

    These columns aggregate all read-lock operations. They are the same as the sum of the corresponding xxx_READ_NORMAL, xxx_READ_WITH_SHARED_LOCKS, xxx_READ_HIGH_PRIORITY, and xxx_READ_NO_INSERT columns.

  • COUNT_WRITE, SUM_TIMER_WRITE, MIN_TIMER_WRITE, AVG_TIMER_WRITE, MAX_TIMER_WRITE

    These columns aggregate all write-lock operations. They are the same as the sum of the corresponding xxx_WRITE_ALLOW_WRITE, xxx_WRITE_CONCURRENT_INSERT, xxx_WRITE_LOW_PRIORITY, and xxx_WRITE_NORMAL columns.

  • COUNT_READ_NORMAL, SUM_TIMER_READ_NORMAL, MIN_TIMER_READ_NORMAL, AVG_TIMER_READ_NORMAL, MAX_TIMER_READ_NORMAL

    These columns aggregate internal read locks.

  • COUNT_READ_WITH_SHARED_LOCKS, SUM_TIMER_READ_WITH_SHARED_LOCKS, MIN_TIMER_READ_WITH_SHARED_LOCKS, AVG_TIMER_READ_WITH_SHARED_LOCKS, MAX_TIMER_READ_WITH_SHARED_LOCKS

    These columns aggregate internal read locks.

  • COUNT_READ_HIGH_PRIORITY, SUM_TIMER_READ_HIGH_PRIORITY, MIN_TIMER_READ_HIGH_PRIORITY, AVG_TIMER_READ_HIGH_PRIORITY, MAX_TIMER_READ_HIGH_PRIORITY

    These columns aggregate internal read locks.

  • COUNT_READ_NO_INSERT, SUM_TIMER_READ_NO_INSERT, MIN_TIMER_READ_NO_INSERT, AVG_TIMER_READ_NO_INSERT, MAX_TIMER_READ_NO_INSERT

    These columns aggregate internal read locks.

  • COUNT_READ_EXTERNAL, SUM_TIMER_READ_EXTERNAL, MIN_TIMER_READ_EXTERNAL, AVG_TIMER_READ_EXTERNAL, MAX_TIMER_READ_EXTERNAL

    These columns aggregate external read locks.

  • COUNT_WRITE_ALLOW_WRITE, SUM_TIMER_WRITE_ALLOW_WRITE, MIN_TIMER_WRITE_ALLOW_WRITE, AVG_TIMER_WRITE_ALLOW_WRITE, MAX_TIMER_WRITE_ALLOW_WRITE

    These columns aggregate internal write locks.

  • COUNT_WRITE_CONCURRENT_INSERT, SUM_TIMER_WRITE_CONCURRENT_INSERT, MIN_TIMER_WRITE_CONCURRENT_INSERT, AVG_TIMER_WRITE_CONCURRENT_INSERT, MAX_TIMER_WRITE_CONCURRENT_INSERT

    These columns aggregate internal write locks.

  • COUNT_WRITE_LOW_PRIORITY, SUM_TIMER_WRITE_LOW_PRIORITY, MIN_TIMER_WRITE_LOW_PRIORITY, AVG_TIMER_WRITE_LOW_PRIORITY, MAX_TIMER_WRITE_LOW_PRIORITY

    These columns aggregate internal write locks.

  • COUNT_WRITE_NORMAL, SUM_TIMER_WRITE_NORMAL, MIN_TIMER_WRITE_NORMAL, AVG_TIMER_WRITE_NORMAL, MAX_TIMER_WRITE_NORMAL

    These columns aggregate internal write locks.

  • COUNT_WRITE_EXTERNAL, SUM_TIMER_WRITE_EXTERNAL, MIN_TIMER_WRITE_EXTERNAL, AVG_TIMER_WRITE_EXTERNAL, MAX_TIMER_WRITE_EXTERNAL

    These columns aggregate external write locks.

TRUNCATE TABLE is permitted for table lock summary tables. It resets the summary columns to zero rather than removing rows.

24.10.15.8 Socket Summary Tables

These socket summary tables aggregate timer and byte count information for socket operations:

  • socket_summary_by_event_name: Aggregate timer and byte count statistics generated by the wait/io/socket/* instruments for all socket I/O operations, per socket instrument.

  • socket_summary_by_instance: Aggregate timer and byte count statistics generated by the wait/io/socket/* instruments for all socket I/O operations, per socket instance. When a connection terminates, the row in socket_summary_by_instance corresponding to it is deleted.

The socket summary tables do not aggregate waits generated by idle events while sockets are waiting for the next request from the client. For idle event aggregations, use the wait-event summary tables; see Section 24.10.15.1, “Wait Event Summary Tables”.

Each socket summary table has one or more grouping columns to indicate how the table aggregates events. Event names refer to names of event instruments in the setup_instruments table.

Each socket summary table has these summary columns containing aggregated values:

  • COUNT_STAR, SUM_TIMER_WAIT, MIN_TIMER_WAIT, AVG_TIMER_WAIT, MAX_TIMER_WAIT

    These columns aggregate all operations.

  • COUNT_READ, SUM_TIMER_READ, MIN_TIMER_READ, AVG_TIMER_READ, MAX_TIMER_READ, SUM_NUMBER_OF_BYTES_READ

    These columns aggregate all receive operations (RECV, RECVFROM, and RECVMSG).

  • COUNT_WRITE, SUM_TIMER_WRITE, MIN_TIMER_WRITE, AVG_TIMER_WRITE, MAX_TIMER_WRITE, SUM_NUMBER_OF_BYTES_WRITE

    These columns aggregate all send operations (SEND, SENDTO, and SENDMSG).

  • COUNT_MISC, SUM_TIMER_MISC, MIN_TIMER_MISC, AVG_TIMER_MISC, MAX_TIMER_MISC

    These columns aggregate all other socket operations, such as CONNECT, LISTEN, ACCEPT, CLOSE, and SHUTDOWN. There are no byte counts for these operations.

The socket_summary_by_instance table also has an EVENT_NAME column that indicates the class of the socket: client_connection, server_tcpip_socket, server_unix_socket. This column can be grouped on to isolate, for example, client activity from that of the server listening sockets.

TRUNCATE TABLE is permitted for socket summary tables. Except for events_statements_summary_by_digest, tt resets the summary columns to zero rather than removing rows.

24.10.15.9 Memory Summary Tables

The Performance Schema instruments memory usage and aggregates memory usage statistics, detailed by these factors:

  • Type of memory used (various caches, internal buffers, and so forth)

  • Thread, account, user, host indirectly performing the memory operation

The Performance Schema instruments the following aspects of memory use

  • Memory sizes used

  • Operation counts

  • Low and high water marks

Memory sizes help to understand or tune the memory consumption of the server.

Operation counts help to understand or tune the overall pressure the server is putting on the memory allocator, which has an impact on performance. Allocating a single byte one million times is not the same as allocating one million bytes a single time; tracking both sizes and counts can expose the difference.

Low and high water marks are critical to detect workload spikes, overall workload stability, and possible memory leaks.

Memory summary tables do not contain timing information because memory events are not timed.

Collection of memory information is described in Memory Instrumentation Behavior.

Example memory event summary information:

mysql> SELECT * FROM memory_summary_global_by_event_name
       WHERE EVENT_NAME = 'memory/sql/TABLE'\G
*************************** 1. row ***************************
                  EVENT_NAME: memory/sql/TABLE
                 COUNT_ALLOC: 1381
                  COUNT_FREE: 924
   SUM_NUMBER_OF_BYTES_ALLOC: 2059873
    SUM_NUMBER_OF_BYTES_FREE: 1407432
              LOW_COUNT_USED: 0
          CURRENT_COUNT_USED: 457
             HIGH_COUNT_USED: 461
    LOW_NUMBER_OF_BYTES_USED: 0
CURRENT_NUMBER_OF_BYTES_USED: 652441
   HIGH_NUMBER_OF_BYTES_USED: 669269

Each memory summary table has one or more grouping columns to indicate how the table aggregates events. Event names refer to names of event instruments in the setup_instruments table.

Each memory summary table has these summary columns containing aggregated values:

  • COUNT_ALLOC, COUNT_FREE

    The aggregated numbers of calls to malloc-like and free-like functions.

  • SUM_NUMBER_OF_BYTES_ALLOC, SUM_NUMBER_OF_BYTES_FREE

    The aggregated sizes of allocated and freed memory blocks.

  • CURRENT_COUNT_USED

    The aggregated number of currently allocated blocks that have not been freed yet. This is a convenience column, equal to COUNT_ALLOCCOUNT_FREE.

  • CURRENT_NUMBER_OF_BYTES_USED

    The aggregated size of currently allocated memory blocks that have not been freed yet. This is a convenience column, equal to SUM_NUMBER_OF_BYTES_ALLOCSUM_NUMBER_OF_BYTES_FREE.

  • LOW_COUNT_USED, HIGH_COUNT_USED

    The low and high water marks corresponding to the CURRENT_COUNT_USED column.

  • LOW_NUMBER_OF_BYTES_USED, HIGH_NUMBER_OF_BYTES_USED

    The low and high water marks corresponding to the CURRENT_NUMBER_OF_BYTES_USED column.

TRUNCATE TABLE is permitted for memory summary tables. It has these effects:

  • In general, truncation resets the baseline for statistics, but does not change the server state. That is, truncating a memory table does not free memory.

  • COUNT_ALLOC and COUNT_FREE are reset to a new baseline, by reducing each counter by the same value.

  • Likewise, SUM_NUMBER_OF_BYTES_ALLOC and SUM_NUMBER_OF_BYTES_FREE are reset to a new baseline.

  • LOW_COUNT_USED and HIGH_COUNT_USED are reset to CURRENT_COUNT_USED.

  • LOW_NUMBER_OF_BYTES_USED and HIGH_NUMBER_OF_BYTES_USED are reset to CURRENT_NUMBER_OF_BYTES_USED.

In addition, each memory summary table that is aggregated by account, host, user, or thread is implicitly truncated by truncation of the connection table on which it depends, or truncation of memory_summary_global_by_event_name. For details, see Section 24.10.8, “Performance Schema Connection Tables”.

Memory Instrumentation Behavior

Most memory instrumentation is disabled by default, and can be enabled or disabled dynamically by updating the ENABLED column of the relevant instruments in the setup_instruments table. Memory instruments have names of the form memory/code_area/instrument_name.

To enable all memory instruments, execute this statement:

mysql> UPDATE setup_instruments SET ENABLED='YES'
       WHERE NAME LIKE 'memory/%';

Instruments named with the prefix memory/performance_schema/ expose how much memory is allocated for internal buffers in the Performance Schema itself. The memory/performance_schema/ instruments are built in, always enabled, and cannot be disabled at startup or runtime. The built-in memory instruments are displayed only in the memory_summary_global_by_event_name table.

For memory instruments, the TIMED column in setup_instruments is ignored because memory operations are not timed.

When a thread in the server executes a memory allocation that has been instrumented, these rules apply:

  • If the thread is not instrumented or the memory instrument is not enabled, the memory block allocated is not instrumented.

  • Otherwise (that is, both the thread and the instrument are enabled), the memory block allocated is instrumented.

For deallocation, these rules apply:

  • If a thread is instrumented, and a memory block is not instrumented, the free operation is not instrumented; no statistics are changed.

  • If a thread is not instrumented, and a memory block is instrumented, the free operation is instrumented, and statistics are changed.

For the per-thread statistics, the following rules apply.

When an instrumented memory block of size N is allocated, the Performance Schema makes these updates to memory summary table columns:

  • COUNT_ALLOC: Increased by 1

  • CURRENT_COUNT_USED: Increased by 1

  • HIGH_COUNT_USED: Increased if CURRENT_COUNT_USED is a new maximum

  • SUM_NUMBER_OF_BYTES_ALLOC: Increased by N

  • CURRENT_NUMBER_OF_BYTES_USED: Increased by N

  • HIGH_NUMBER_OF_BYTES_USED: Increased if CURRENT_NUMBER_OF_BYTES_USED is a new maximum

When an instrumented memory block is deallocated, the Performance Schema makes these updates to memory summary table columns:

  • COUNT_FREE: Increased by 1

  • CURRENT_COUNT_USED: Decreased by 1

  • LOW_COUNT_USED: Decreased if CURRENT_COUNT_USED is a new minimum

  • SUM_NUMBER_OF_BYTES_FREE: Increased by N

  • CURRENT_NUMBER_OF_BYTES_USED: Decreased by N

  • LOW_NUMBER_OF_BYTES_USED: Decreased if CURRENT_NUMBER_OF_BYTES_USED is a new minimum

For higher-level aggregates (global, by account, by user, by host), the same rules apply as expected for low and high water marks.

  • LOW_COUNT_USED and LOW_NUMBER_OF_BYTES_USED are lower estimates. The value reported by the Performance Schema is guaranteed to be less than or equal to the lowest count or size of memory effectively used at runtime.

  • HIGH_COUNT_USED and HIGH_NUMBER_OF_BYTES_USED are higher estimates. The value reported by the Performance Schema is guaranteed to be greater than or equal to the highest count or size of memory effectively used at runtime.

For lower estimates in summary tables other than memory_summary_global_by_event_name, it is possible for values to go negative if memory ownership is transferred between threads.

Here is an example of estimate computation; but note that estimate implementation is subject to change:

Thread 1 uses memory in the range from 1MB to 2MB during execution, as reported by the LOW_NUMBER_OF_BYTES_USED and HIGH_NUMBER_OF_BYTES_USED columns of the memory_summary_by_thread_by_event_name table.

Thread 2 uses memory in the range from 10MB to 12MB during execution, as reported likewise.

When these two threads belong to the same user account, the per-account summary estimates that this account used memory in the range from 11MB to 14MB. That is, the LOW_NUMBER_OF_BYTES_USED for the higher level aggregate is the sum of each LOW_NUMBER_OF_BYTES_USED (assuming the worst case). Likewise, the HIGH_NUMBER_OF_BYTES_USED for the higher level aggregate is the sum of each HIGH_NUMBER_OF_BYTES_USED (assuming the worst case).

11MB is a lower estimate that can occur only if both threads hit the low usage mark at the same time.

14MB is a higher estimate that can occur only if both threads hit the high usage mark at the same time.

The real memory usage for this account could have been in the range from 11.5MB to 13.5MB.

For capacity planning, reporting the worst case is actually the desired behavior, as it shows what can potentially happen when sessions are uncorrelated, which is typically the case.

24.10.15.10 Status Variable Summary Tables

Note

The value of the show_compatibility_56 system variable affects the information available from the tables described here. For details, see the description of that variable in Section 6.1.5, “Server System Variables”.

As of MySQL 5.7.6, the Performance Schema makes status variable information available in the tables described in Section 24.10.14, “Performance Schema Status Variable Tables”. It also makes aggregated status variable information available in summary tables, described here. Each status variable summary table has one or more grouping columns to indicate how the table aggregates status values:

  • status_by_account has USER, HOST, and VARIABLE_NAME columns to summarize status variables by account.

  • status_by_host has HOST and VARIABLE_NAME columns to summarize status variables by the host from which clients connected.

  • status_by_user has USER and VARIABLE_NAME columns to summarize status variables by client user name.

Each status variable summary table has this summary column containing aggregated values:

  • VARIABLE_VALUE

    The aggregated status variable value for active and terminated sessions.

The meaning of account in these tables is similar to its meaning in the MySQL grant tables in the mysql system database, in the sense that the term refers to a combination of user and host values. They differ in that, for grant tables, the host part of an account can be a pattern, whereas for Performance Schema tables, the host value is always a specific nonpattern host name.

Account status is collected when sessions terminate. The session status counters are added to the global status counters and the corresponding account status counters. If account statistics are not collected, the session status is added to host and user status, if host and user status are collected.

Account, host, and user statistics are not collected if the performance_schema_accounts_size, performance_schema_hosts_size, and performance_schema_users_size system variables, respectively, are set to 0.

The Performance Schema supports TRUNCATE TABLE for status variable summary tables as follows; in all cases, status for active sessions is unaffected:

  • status_by_account: Aggregates account status from terminated sessions to user and host status, then resets account status.

  • status_by_host: Resets aggregated host status from terminated sessions.

  • status_by_user: Resets aggregated user status from terminated sessions.

FLUSH STATUS adds the session status from all active sessions to the global status variables, resets the status of all active sessions, and resets account, host, and user status values aggregated from disconnected sessions.

24.10.16 Performance Schema Miscellaneous Tables

The following sections describe tables that do not fall into the table categories discussed in the preceding sections:

24.10.16.1 The host_cache Table

The host_cache table provides access to the contents of the host cache, which contains client host name and IP address information and is used to avoid DNS lookups. (See Section 9.12.5.2, “DNS Lookup Optimization and the Host Cache”.) The host_cache table exposes the contents of the host cache so that it can be examined using SELECT statements. The Performance Schema must be enabled or this table is empty.

The host_cache table has these columns:

  • IP

    The IP address of the client that connected to the server, expressed as a string.

  • HOST

    The resolved DNS host name for that client IP, or NULL if the name is unknown.

  • HOST_VALIDATED

    Whether the IP-to-host name-to-IP DNS resolution was performed successfully for the client IP. If HOST_VALIDATED is YES, the HOST column is used as the host name corresponding to the IP so that calls to DNS can be avoided. While HOST_VALIDATED is NO, DNS resolution is attempted again for each connect, until it eventually completes with either a valid result or a permanent error. This information enables the server to avoid caching bad or missing host names during temporary DNS failures, which would affect clients forever.

  • SUM_CONNECT_ERRORS

    The number of connection errors that are deemed blocking (assessed against the max_connect_errors system variable). Only protocol handshake errors are counted, and only for hosts that passed validation (HOST_VALIDATED = YES).

  • COUNT_HOST_BLOCKED_ERRORS

    The number of connections that were blocked because SUM_CONNECT_ERRORS exceeded the value of the max_connect_errors system variable.

  • COUNT_NAMEINFO_TRANSIENT_ERRORS

    The number of transient errors during IP-to-host name DNS resolution.

  • COUNT_NAMEINFO_PERMANENT_ERRORS

    The number of permanent errors during IP-to-host name DNS resolution.

  • COUNT_FORMAT_ERRORS

    The number of host name format errors. MySQL does not perform matching of Host column values in the mysql.user table against host names for which one or more of the initial components of the name are entirely numeric, such as 1.2.example.com. The client IP address is used instead. For the rationale why this type of matching does not occur, see Section 7.2.3, “Specifying Account Names”.

  • COUNT_ADDRINFO_TRANSIENT_ERRORS

    The number of transient errors during host name-to-IP reverse DNS resolution.

  • COUNT_ADDRINFO_PERMANENT_ERRORS

    The number of permanent errors during host name-to-IP reverse DNS resolution.

  • COUNT_FCRDNS_ERRORS

    The number of forward-confirmed reverse DNS errors. These errors occur when IP-to-host name-to-IP DNS resolution produces an IP address that does not match the client originating IP address.

  • COUNT_HOST_ACL_ERRORS

    The number of errors that occur because no user from the client host can possibly log in. In such cases, the server returns ER_HOST_NOT_PRIVILEGED and does not even ask for a user name or password.

  • COUNT_NO_AUTH_PLUGIN_ERRORS

    The number of errors due to requests for an unavailable authentication plugin. A plugin can be unavailable if, for example, it was never loaded or a load attempt failed.

  • COUNT_AUTH_PLUGIN_ERRORS

    The number of errors reported by authentication plugins.

    An authentication plugin can report different error codes to indicate the root cause of a failure. Depending on the type of error, one of these columns is incremented: COUNT_AUTHENTICATION_ERRORS, COUNT_AUTH_PLUGIN_ERRORS, COUNT_HANDSHAKE_ERRORS. New return codes are an optional extension to the existing plugin API. Unknown or unexpected plugin errors are counted in the COUNT_AUTH_PLUGIN_ERRORS column.

  • COUNT_HANDSHAKE_ERRORS

    The number of errors detected at the wire protocol level.

  • COUNT_PROXY_USER_ERRORS

    The number of errors detected when a proxy user A is proxied to another user B who does not exist.

  • COUNT_PROXY_USER_ACL_ERRORS

    The number of errors detected when a proxy user A is proxied to another user B who does exist but for whom A does not have the PROXY privilege.

  • COUNT_AUTHENTICATION_ERRORS

    The number of errors caused by failed authentication.

  • COUNT_SSL_ERRORS

    The number of errors due to SSL problems.

  • COUNT_MAX_USER_CONNECTIONS_ERRORS

    The number of errors caused by exceeding per-user connection quotas. See Section 7.3.4, “Setting Account Resource Limits”.

  • COUNT_MAX_USER_CONNECTIONS_PER_HOUR_ERRORS

    The number of errors caused by exceeding per-user connections-per-hour quotas. See Section 7.3.4, “Setting Account Resource Limits”.

  • COUNT_DEFAULT_DATABASE_ERRORS

    The number of errors related to the default database. For example, the database did not exist or the user had no privileges for accessing it.

  • COUNT_INIT_CONNECT_ERRORS

    The number of errors caused by execution failures of statements in the init_connect system variable value.

  • COUNT_LOCAL_ERRORS

    The number of errors local to the server implementation and not related to the network, authentication, or authorization. For example, out-of-memory conditions fall into this category.

  • COUNT_UNKNOWN_ERRORS

    The number of other, unknown errors not accounted for by other columns in this table. This column is reserved for future use, in case new error conditions must be reported, and if preserving the backward compatibility and table structure of the host_cache table is required.

  • FIRST_SEEN

    The timestamp of the first connection attempt seen from the client in the IP column.

  • LAST_SEEN

    The timestamp of the last connection attempt seen from the client in the IP column.

  • FIRST_ERROR_SEEN

    The timestamp of the first error seen from the client in the IP column.

  • LAST_ERROR_SEEN

    The timestamp of the last error seen from the client in the IP column.

FLUSH HOSTS and TRUNCATE TABLE host_cache have the same effect: They clear the host cache. This also removes rows from the host_cache table (because it is the visible representation of the cache) and unblocks any blocked hosts (see Section B.5.2.6, “Host 'host_name' is blocked”.) FLUSH HOSTS requires the RELOAD privilege. TRUNCATE TABLE requires the DROP privilege for the host_cache table.

24.10.16.2 The performance_timers Table

The performance_timers table shows which event timers are available:

mysql> SELECT * FROM performance_timers;
+-------------+-----------------+------------------+----------------+
| TIMER_NAME  | TIMER_FREQUENCY | TIMER_RESOLUTION | TIMER_OVERHEAD |
+-------------+-----------------+------------------+----------------+
| CYCLE       |      2389029850 |                1 |             72 |
| NANOSECOND  |      1000000000 |                1 |            112 |
| MICROSECOND |         1000000 |                1 |            136 |
| MILLISECOND |            1036 |                1 |            168 |
| TICK        |             105 |                1 |           2416 |
+-------------+-----------------+------------------+----------------+

The timers in setup_timers that you can use are those that do not have NULL in the other columns. If the values associated with a given timer name are NULL, that timer is not supported on your platform.

The performance_timers table has these columns:

  • TIMER_NAME

    The name by which to refer to the timer when configuring the setup_timers table.

  • TIMER_FREQUENCY

    The number of timer units per second. For a cycle timer, the frequency is generally related to the CPU speed. For example, on a system with a 2.4GHz processor, the CYCLE may be close to 2400000000.

  • TIMER_RESOLUTION

    Indicates the number of timer units by which timer values increase. If a timer has a resolution of 10, its value increases by 10 each time.

  • TIMER_OVERHEAD

    The minimal number of cycles of overhead to obtain one timing with the given timer. The Performance Schema determines this value by invoking the timer 20 times during initialization and picking the smallest value. The total overhead really is twice this amount because the instrumentation invokes the timer at the start and end of each event. The timer code is called only for timed events, so this overhead does not apply for nontimed events.

TRUNCATE TABLE is not permitted for the performance_timers table.

24.10.16.3 The threads Table

The threads table contains a row for each server thread. Each row contains information about a thread and indicates whether monitoring and historical event logging are enabled for it:

mysql> SELECT * FROM threads\G
*************************** 1. row ***************************
          THREAD_ID: 1
               NAME: thread/sql/main
               TYPE: BACKGROUND
     PROCESSLIST_ID: NULL
   PROCESSLIST_USER: NULL
   PROCESSLIST_HOST: NULL
     PROCESSLIST_DB: NULL
PROCESSLIST_COMMAND: NULL
   PROCESSLIST_TIME: 80284
  PROCESSLIST_STATE: NULL
   PROCESSLIST_INFO: NULL
   PARENT_THREAD_ID: NULL
               ROLE: NULL
       INSTRUMENTED: YES
            HISTORY: YES
    CONNECTION_TYPE: NULL
       THREAD_OS_ID: 489803
...
*************************** 4. row ***************************
          THREAD_ID: 51
               NAME: thread/sql/one_connection
               TYPE: FOREGROUND
     PROCESSLIST_ID: 34
   PROCESSLIST_USER: isabella
   PROCESSLIST_HOST: localhost
     PROCESSLIST_DB: performance_schema
PROCESSLIST_COMMAND: Query
   PROCESSLIST_TIME: 0
  PROCESSLIST_STATE: Sending data
   PROCESSLIST_INFO: SELECT * FROM threads
   PARENT_THREAD_ID: 1
               ROLE: NULL
       INSTRUMENTED: YES
            HISTORY: YES
    CONNECTION_TYPE: SSL/TLS
       THREAD_OS_ID: 755399
...

When the Performance Schema initializes, it populates the threads table based on the threads in existence then. Thereafter, a new row is added each time the server creates a thread.

The INSTRUMENTED and HISTORY column values for new threads are determined by the contents of the setup_actors table. For information about how to use the setup_actors table to control these columns, see Section 24.3.6, “Pre-Filtering by Thread”.

Removal of rows from the threads table occurs when threads end. For a thread associated with a client session, removal occurs when the session ends. If a client has auto-reconnect enabled and the session reconnects after a disconnect, the session becomes associated with a new row in the threads table that has a different PROCESSLIST_ID value. The initial INSTRUMENTED and HISTORY values for the new thread may be different from those of the original thread: The setup_actors table may have changed in the meantime, and if the INSTRUMENTED or HISTORY value for the original thread was changed after the row was initialized, the change does not carry over to the new thread.

The threads table columns with names having a prefix of PROCESSLIST_ provide information similar to that available from the INFORMATION_SCHEMA.PROCESSLIST table or the SHOW PROCESSLIST statement. Thus, all three sources provide thread-monitoring information. Use of threads differs from use of the other two sources in these ways:

  • Access to threads does not require a mutex and has minimal impact on server performance. INFORMATION_SCHEMA.PROCESSLIST and SHOW PROCESSLIST have negative performance consequences because they require a mutex.

  • threads provides additional information for each thread, such as whether it is a foreground or background thread, and the location within the server associated with the thread.

  • threads provides information about background threads, so it can be used to monitor activity the other thread information sources cannot.

  • You can enable or disable thread monitoring (that is, whether events executed by the thread are instrumented) and historical event logging. To control the initial INSTRUMENTED and HISTORY values for new foreground threads, use the setup_actors table. To control these aspects of existing threads, set the INSTRUMENTED and HISTORY columns of threads table rows. (For more information about the conditions under which thread monitoring and historical event logging occur, see the descriptions of the INSTRUMENTED and HISTORY columns.)

For these reasons, DBAs who perform server monitoring using INFORMATION_SCHEMA.PROCESSLIST or SHOW PROCESSLIST may wish to monitor using the threads table instead.

Note

For INFORMATION_SCHEMA.PROCESSLIST and SHOW PROCESSLIST, information about threads for other users is shown only if the current user has the PROCESS privilege. That is not true of the threads table; all rows are shown to any user who has the SELECT privilege for the table. Users who should not be able to see threads for other users should not be given that privilege.

The threads table has these columns:

  • THREAD_ID

    A unique thread identifier.

  • NAME

    The name associated with the thread instrumentation code in the server. For example, thread/sql/one_connection corresponds to the thread function in the code responsible for handling a user connection, and thread/sql/main stands for the main() function of the server.

  • TYPE

    The thread type, either FOREGROUND or BACKGROUND. User connection threads are foreground threads. Threads associated with internal server activity are background threads. Examples are internal InnoDB threads, binlog dump threads sending information to slaves, and slave I/O and SQL threads.

  • PROCESSLIST_ID

    For threads that are displayed in the INFORMATION_SCHEMA.PROCESSLIST table, this is the same value displayed in the ID column of that table. It is also the value displayed in the Id column of SHOW PROCESSLIST output, and the value that CONNECTION_ID() would return within that thread.

    For background threads (threads not associated with a user connection), PROCESSLIST_ID is NULL, so the values are not unique.

  • PROCESSLIST_USER

    The user associated with a foreground thread, NULL for a background thread.

  • PROCESSLIST_HOST

    The host name of the client associated with a foreground thread, NULL for a background thread.

    Unlike the HOST column of the INFORMATION_SCHEMA PROCESSLIST table or the Host column of SHOW PROCESSLIST output, the PROCESSLIST_HOST column does not include the port number for TCP/IP connections. To obtain this information from the Performance Schema, enable the socket instrumentation (which is not enabled by default) and examine the socket_instances table:

    mysql> SELECT * FROM setup_instruments WHERE NAME LIKE 'wait/io/socket%';
    +----------------------------------------+---------+-------+
    | NAME                                   | ENABLED | TIMED |
    +----------------------------------------+---------+-------+
    | wait/io/socket/sql/server_tcpip_socket | NO      | NO    |
    | wait/io/socket/sql/server_unix_socket  | NO      | NO    |
    | wait/io/socket/sql/client_connection   | NO      | NO    |
    +----------------------------------------+---------+-------+
    3 rows in set (0.01 sec)
    
    mysql> UPDATE setup_instruments SET ENABLED='YES' WHERE NAME LIKE 'wait/io/socket%';
    Query OK, 3 rows affected (0.00 sec)
    Rows matched: 3  Changed: 3  Warnings: 0
    
    mysql> SELECT * FROM socket_instances\G
    *************************** 1. row ***************************
               EVENT_NAME: wait/io/socket/sql/client_connection
    OBJECT_INSTANCE_BEGIN: 140612577298432
                THREAD_ID: 31
                SOCKET_ID: 53
                       IP: ::ffff:127.0.0.1
                     PORT: 55642
                    STATE: ACTIVE
    ...
    
  • PROCESSLIST_DB

    The default database for the thread, or NULL if there is none.

  • PROCESSLIST_COMMAND

    For foreground threads, the type of command the thread is executing on behalf of the client, or Sleep if the session is idle. For descriptions of thread commands, see Section 9.14, “Examining Thread Information”. The value of this column corresponds to the COM_xxx commands of the client/server protocol and Com_xxx status variables. See Section 6.1.7, “Server Status Variables”

    Background threads do not execute commands on behalf of clients, so this column may be NULL.

  • PROCESSLIST_TIME

    The time in seconds that the thread has been in its current state.

  • PROCESSLIST_STATE

    An action, event, or state that indicates what the thread is doing. For descriptions of PROCESSLIST_STATE values, see Section 9.14, “Examining Thread Information”. If the value if NULL, the thread may correspond to an idle client session or the work it is doing is not instrumented with stages.

    Most states correspond to very quick operations. If a thread stays in a given state for many seconds, there might be a problem that bears investigation.

  • PROCESSLIST_INFO

    The statement the thread is executing, or NULL if it is not executing any statement. The statement might be the one sent to the server, or an innermost statement if the statement executes other statements. For example, if a CALL statement executes a stored procedure that is executing a SELECT statement, the PROCESSLIST_INFO value shows the SELECT statement.

  • PARENT_THREAD_ID

    If this thread is a subthread (spawned by another thread), this is the THREAD_ID value of the spawning thread.

  • ROLE

    Unused.

  • INSTRUMENTED

    Whether events executed by the thread are instrumented. The value is YES or NO.

    • For foreground threads, the initial INSTRUMENTED value is determined by whether the user account associated with the thread matches any row in the setup_actors table. Matching is based on the values of the PROCESSLIST_USER and PROCESSLIST_HOST columns.

      If the thread spawns a subthread, matching occurs again for the threads table row created for the subthread.

    • For background threads, INSTRUMENTED is YES by default. setup_actors is not consulted because there is no associated user for background threads.

    • For any thread, its INSTRUMENTED value can be changed during the lifetime of the thread.

    For monitoring of events executed by the thread to occur, these things must be true:

    • The thread_instrumentation consumer in the setup_consumers table must be YES.

    • The threads.INSTRUMENTED column must be YES.

    • Monitoring occurs only for those thread events produced from instruments that have the ENABLED column set to YES in the setup_instruments table.

  • HISTORY

    Whether to log historical events for the thread. The value is YES or NO.

    • For foreground threads, the initial HISTORY value is determined by whether the user account associated with the thread matches any row in the setup_actors table. Matching is based on the values of the PROCESSLIST_USER and PROCESSLIST_HOST columns.

      If the thread spawns a subthread, matching occurs again for the threads table row created for the subthread.

    • For background threads, HISTORY is YES by default. setup_actors is not consulted because there is no associated user for background threads.

    • For any thread, its HISTORY value can be changed during the lifetime of the thread.

    For historical event logging for the thread to occur, these things must be true:

    • The appropriate history-related consumers in the setup_consumers table must be enabled. For example, wait event logging in the events_waits_history and events_waits_history_long tables requires the corresponding events_waits_history and events_waits_history_long consumers to be YES.

    • The threads.HISTORY column must be YES.

    • Logging occurs only for those thread events produced from instruments that have the ENABLED column set to YES in the setup_instruments table.

    The HISTORY column was added in MySQL 5.7.8. For earlier versions in which it is not present, the Performance Schema logs historical events either for all threads or no threads, depending on which history consumers are enabled or disabled.

  • CONNECTION_TYPE

    The protocol used to establish the connection, or NULL for background threads. Permitted values are TCP/IP (TCP/IP connection established without SSL), SSL/TLS (TCP/IP connection established with SSL), Socket (Unix socket file connection), Named Pipe (Windows named pipe connection), and Shared Memory (Windows shared memory connection).

    This column was added in MySQL 5.7.8.

  • THREAD_OS_ID

    The thread or task identifier as defined by the underlying operating system, if there is one:

    • When a MySQL thread is associated with the same operating system thread for its lifetime, THREAD_OS_ID contains the operating system thread ID.

    • When a MySQL thread is not associated with the same operating system thread for its lifetime, THREAD_OS_ID contains NULL. This is typical for user sessions when the thread pool plugin is used (see Section 6.5.4, “MySQL Enterprise Thread Pool”).

    For Windows, THREAD_OS_ID corresponds to the thread ID visible in Process Explorer (https://technet.microsoft.com/en-us/sysinternals/bb896653.aspx).

    For Linux, THREAD_OS_ID corresponds to the value of the gettid() function. This value is exposed, for example, using the perf or ps -L commands, or in the proc file system (/proc/[pid]/task/[tid]). For more information, see the perf-stat(1), ps(1), and proc(5) man pages.

    This column was added in MySQL 5.7.9.

TRUNCATE TABLE is not permitted for the threads table.

24.11 Performance Schema Option and Variable Reference

Table 24.3 Performance Schema Variable Reference

NameCmd-LineOption FileSystem VarStatus VarVar ScopeDynamic
performance_schemaYesYesYes GlobalNo
Performance_schema_accounts_lost   YesGlobalNo
performance_schema_accounts_sizeYesYesYes GlobalNo
Performance_schema_cond_classes_lost   YesGlobalNo
Performance_schema_cond_instances_lost   YesGlobalNo
performance-schema-consumer-events-stages-currentYesYes    
performance-schema-consumer-events-stages-historyYesYes    
performance-schema-consumer-events-stages-history-longYesYes    
performance-schema-consumer-events-statements-currentYesYes    
performance-schema-consumer-events-statements-historyYesYes    
performance-schema-consumer-events-statements-history-longYesYes    
performance-schema-consumer-events-transactions-currentYesYes    
performance-schema-consumer-events-transactions-historyYesYes    
performance-schema-consumer-events-transactions-history-longYesYes    
performance-schema-consumer-events-waits-currentYesYes    
performance-schema-consumer-events-waits-historyYesYes    
performance-schema-consumer-events-waits-history-longYesYes    
performance-schema-consumer-global-instrumentationYesYes    
performance-schema-consumer-statements-digestYesYes    
performance-schema-consumer-thread-instrumentationYesYes    
Performance_schema_digest_lost   YesGlobalNo
performance_schema_digests_sizeYesYesYes GlobalNo
performance_schema_events_stages_history_long_sizeYesYesYes GlobalNo
performance_schema_events_stages_history_sizeYesYesYes GlobalNo
performance_schema_events_statements_history_long_sizeYesYesYes GlobalNo
performance_schema_events_statements_history_sizeYesYesYes GlobalNo
performance_schema_events_transactions_history_long_sizeYesYesYes GlobalNo
performance_schema_events_transactions_history_sizeYesYesYes GlobalNo
performance_schema_events_waits_history_long_sizeYesYesYes GlobalNo
performance_schema_events_waits_history_sizeYesYesYes GlobalNo
Performance_schema_file_classes_lost   YesGlobalNo
Performance_schema_file_handles_lost   YesGlobalNo
Performance_schema_file_instances_lost   YesGlobalNo
Performance_schema_hosts_lost   YesGlobalNo
performance_schema_hosts_sizeYesYesYes GlobalNo
performance-schema-instrumentYesYes    
Performance_schema_locker_lost   YesGlobalNo
performance_schema_max_cond_classesYesYesYes GlobalNo
performance_schema_max_cond_instancesYesYesYes GlobalNo
performance_schema_max_digest_lengthYesYesYes GlobalNo
performance_schema_max_file_classesYesYesYes GlobalNo
performance_schema_max_file_handlesYesYesYes GlobalNo
performance_schema_max_file_instancesYesYesYes GlobalNo
performance_schema_max_memory_classesYesYesYes GlobalNo
performance_schema_max_metadata_locksYesYesYes GlobalNo
performance_schema_max_mutex_classesYesYesYes GlobalNo
performance_schema_max_mutex_instancesYesYesYes GlobalNo
performance_schema_max_prepared_statements_instancesYesYesYes GlobalNo
performance_schema_max_program_instancesYesYesYes GlobalNo
performance_schema_max_rwlock_classesYesYesYes GlobalNo
performance_schema_max_rwlock_instancesYesYesYes GlobalNo
performance_schema_max_socket_classesYesYesYes GlobalNo
performance_schema_max_socket_instancesYesYesYes GlobalNo
performance_schema_max_stage_classesYesYesYes GlobalNo
performance_schema_max_statement_classesYesYesYes GlobalNo
performance_schema_max_statement_stackYesYesYes GlobalNo
performance_schema_max_table_handlesYesYesYes GlobalNo
performance_schema_max_table_instancesYesYesYes GlobalNo
performance_schema_max_thread_classesYesYesYes GlobalNo
performance_schema_max_thread_instancesYesYesYes GlobalNo
Performance_schema_memory_classes_lost   YesGlobalNo
Performance_schema_metadata_lock_lost   YesGlobalNo
Performance_schema_mutex_classes_lost   YesGlobalNo
Performance_schema_mutex_instances_lost   YesGlobalNo
Performance_schema_nested_statement_lost   YesGlobalNo
Performance_schema_prepared_statements_lost   YesGlobalNo
Performance_schema_program_lost   YesGlobalNo
Performance_schema_rwlock_classes_lost   YesGlobalNo
Performance_schema_rwlock_instances_lost   YesGlobalNo
Performance_schema_session_connect_attrs_lost   YesGlobalNo
performance_schema_session_connect_attrs_sizeYesYesYes GlobalNo
performance_schema_setup_actors_sizeYesYesYes GlobalNo
performance_schema_setup_objects_sizeYesYesYes GlobalNo
Performance_schema_socket_classes_lost   YesGlobalNo
Performance_schema_socket_instances_lost   YesGlobalNo
Performance_schema_stage_classes_lost   YesGlobalNo
Performance_schema_statement_classes_lost   YesGlobalNo
Performance_schema_table_handles_lost   YesGlobalNo
Performance_schema_table_instances_lost   YesGlobalNo
Performance_schema_thread_classes_lost   YesGlobalNo
Performance_schema_thread_instances_lost   YesGlobalNo
Performance_schema_users_lost   YesGlobalNo
performance_schema_users_sizeYesYesYes GlobalNo

24.12 Performance Schema Command Options

Performance Schema parameters can be specified at server startup on the command line or in option files to configure Performance Schema instruments and consumers. Runtime configuration is also possible in many cases (see Section 24.3, “Performance Schema Runtime Configuration”), but startup configuration must be used when runtime configuration is too late to affect instruments that have already been initialized during the startup process.

Performance Schema consumers and instruments can be configured at startup using the following syntax. For additional details, see Section 24.2.2, “Performance Schema Startup Configuration”.

The following items configure individual consumers:

24.13 Performance Schema System Variables

The Performance Schema implements several system variables that provide configuration information:

mysql> SHOW VARIABLES LIKE 'perf%';
+----------------------------------------------------------+-------+
| Variable_name                                            | Value |
+----------------------------------------------------------+-------+
| performance_schema                                       | ON    |
| performance_schema_accounts_size                         | -1    |
| performance_schema_digests_size                          | 10000 |
| performance_schema_events_stages_history_long_size       | 10000 |
| performance_schema_events_stages_history_size            | 10    |
| performance_schema_events_statements_history_long_size   | 10000 |
| performance_schema_events_statements_history_size        | 10    |
| performance_schema_events_transactions_history_long_size | 10000 |
| performance_schema_events_transactions_history_size      | 10    |
| performance_schema_events_waits_history_long_size        | 10000 |
| performance_schema_events_waits_history_size             | 10    |
| performance_schema_hosts_size                            | -1    |
| performance_schema_max_cond_classes                      | 80    |
| performance_schema_max_cond_instances                    | -1    |
| performance_schema_max_digest_length                     | 1024  |
| performance_schema_max_file_classes                      | 50    |
| performance_schema_max_file_handles                      | 32768 |
| performance_schema_max_file_instances                    | -1    |
| performance_schema_max_index_stat                        | -1    |
| performance_schema_max_memory_classes                    | 320   |
| performance_schema_max_metadata_locks                    | -1    |
| performance_schema_max_mutex_classes                     | 200   |
| performance_schema_max_mutex_instances                   | -1    |
| performance_schema_max_prepared_statements_instances     | -1    |
| performance_schema_max_program_instances                 | -1    |
| performance_schema_max_rwlock_classes                    | 40    |
| performance_schema_max_rwlock_instances                  | -1    |
| performance_schema_max_socket_classes                    | 10    |
| performance_schema_max_socket_instances                  | -1    |
| performance_schema_max_sql_text_length                   | 1024  |
| performance_schema_max_stage_classes                     | 150   |
| performance_schema_max_statement_classes                 | 192   |
| performance_schema_max_statement_stack                   | 10    |
| performance_schema_max_table_handles                     | -1    |
| performance_schema_max_table_instances                   | -1    |
| performance_schema_max_table_lock_stat                   | -1    |
| performance_schema_max_thread_classes                    | 50    |
| performance_schema_max_thread_instances                  | -1    |
| performance_schema_session_connect_attrs_size            | 512   |
| performance_schema_setup_actors_size                     | -1    |
| performance_schema_setup_objects_size                    | -1    |
| performance_schema_users_size                            | -1    |
+----------------------------------------------------------+-------+

Performance Schema system variables can be set at server startup on the command line or in option files, and many can be set at runtime. See Section 24.11, “Performance Schema Option and Variable Reference”.

The Performance Schema automatically sizes the values of several of its parameters at server startup if they are not set explicitly. For more information, see Section 24.2.2, “Performance Schema Startup Configuration”.

Performance Schema system variables have the following meanings:

24.14 Performance Schema Status Variables

The Performance Schema implements several status variables that provide information about instrumentation that could not be loaded or created due to memory constraints:

mysql> SHOW STATUS LIKE 'perf%';
+-------------------------------------------+-------+
| Variable_name                             | Value |
+-------------------------------------------+-------+
| Performance_schema_accounts_lost          | 0     |
| Performance_schema_cond_classes_lost      | 0     |
| Performance_schema_cond_instances_lost    | 0     |
| Performance_schema_file_classes_lost      | 0     |
| Performance_schema_file_handles_lost      | 0     |
| Performance_schema_file_instances_lost    | 0     |
| Performance_schema_hosts_lost             | 0     |
| Performance_schema_locker_lost            | 0     |
| Performance_schema_mutex_classes_lost     | 0     |
| Performance_schema_mutex_instances_lost   | 0     |
| Performance_schema_rwlock_classes_lost    | 0     |
| Performance_schema_rwlock_instances_lost  | 0     |
| Performance_schema_socket_classes_lost    | 0     |
| Performance_schema_socket_instances_lost  | 0     |
| Performance_schema_stage_classes_lost     | 0     |
| Performance_schema_statement_classes_lost | 0     |
| Performance_schema_table_handles_lost     | 0     |
| Performance_schema_table_instances_lost   | 0     |
| Performance_schema_thread_classes_lost    | 0     |
| Performance_schema_thread_instances_lost  | 0     |
| Performance_schema_users_lost             | 0     |
+-------------------------------------------+-------+

Performance Schema status variables have the following meanings:

For information on using these variables to check Performance Schema status, see Section 24.6, “Performance Schema Status Monitoring”.

24.15 The Performance Schema Memory-Allocation Model

Before MySQL 5.7.6, the Performance Schema used this memory allocation model:

  • Allocate all the memory needed at server startup

  • Never allocate memory during server operation

  • Never free memory during server operation

  • Free all memory used at shutdown

With that model, the Performance Schema potentially allocates a large amount of memory unless explicit configuration is used to minimize particular types of instrumentation.

As of MySQL 5.7.6, the memory model allocates less memory by default under most circumstances:

  • May allocate memory at server startup

  • May allocate additional memory during server operation

  • Never free memory during server operation (although it might be recycled)

  • Free all memory used at shutdown

The result is to relax memory constraints so that the Performance Schema can be used with less configuration, and to decrease the memory footprint so that consumption scales with server load. Memory used depends on the load actually seen, not the load estimated or explicitly configured for.

Several Performance Schema sizing parameters are autoscaled and need not be configured explicitly unless you want to establish an explicit limit on memory allocation:

performance_schema_accounts_size
performance_schema_hosts_size
performance_schema_max_cond_instances
performance_schema_max_file_instances
performance_schema_max_index_stat
performance_schema_max_metadata_locks
performance_schema_max_mutex_instances
performance_schema_max_prepared_statements_instances
performance_schema_max_program_instances
performance_schema_max_rwlock_instances
performance_schema_max_socket_instances
performance_schema_max_table_handles
performance_schema_max_table_instances
performance_schema_max_table_lock_stat
performance_schema_max_thread_instances
performance_schema_users_size

For an autoscaled parameter, configuration works like this:

  • With the value set to -1 (the default), the parameter is autoscaled:

    • The corresponding internal buffer is empty initially and no memory is allocated.

    • As the Performance Schema collects data, memory is allocated in the corresponding buffer. The buffer size is unbounded, and may grow with the load.

  • With the value set to 0:

    • The corresponding internal buffer is empty initially and no memory is allocated.

  • With the value set to N > 0:

    • The corresponding internal buffer is empty initially and no memory is allocated.

    • As the Performance Schema collects data, memory is allocated in the corresponding buffer, until the buffer size reaches N.

    • Once the buffer size reaches N, no more memory is allocated. Data collected by the Performance Schema for this buffer is lost, and any corresponding lost instance counters are incremented.

To see how much memory the Performance Schema is using, check the instruments designed for that purpose. The Performance Schema allocates memory internally and associates each buffer with a dedicated instrument so that memory consumption can be traced to individual buffers. Instruments named with the prefix memory/performance_schema/ expose how much memory is allocated for these internal buffers. The buffers are global to the server, so the instruments are displayed only in the memory_summary_global_by_event_name table, and not in other memory_summary_by_xxx_by_event_name tables.

This query shows the information associated with the memory instruments:

SELECT * FROM memory_summary_global_by_event_name
WHERE EVENT_NAME LIKE 'memory/performance_schema/%';

24.16 Performance Schema and Plugins

Removing a plugin with UNINSTALL PLUGIN does not affect information already collected for code in that plugin. Time spent executing the code while the plugin was loaded was still spent even if the plugin is unloaded later. The associated event information, including aggregate information, remains readable in performance_schema database tables. For additional information about the effect of plugin installation and removal, see Section 24.6, “Performance Schema Status Monitoring”.

A plugin implementor who instruments plugin code should document its instrumentation characteristics to enable those who load the plugin to account for its requirements. For example, a third-party storage engine should include in its documentation how much memory the engine needs for mutex and other instruments.

24.17 Using the Performance Schema to Diagnose Problems

The Performance Schema is a tool to help a DBA do performance tuning by taking real measurements instead of wild guesses. This section demonstrates some ways to use the Performance Schema for this purpose. The discussion here relies on the use of event filtering, which is described in Section 24.3.2, “Performance Schema Event Filtering”.

The following example provides one methodology that you can use to analyze a repeatable problem, such as investigating a performance bottleneck. To begin, you should have a repeatable use case where performance is deemed too slow and needs optimization, and you should enable all instrumentation (no pre-filtering at all).

  1. Run the use case.

  2. Using the Performance Schema tables, analyze the root cause of the performance problem. This analysis will rely heavily on post-filtering.

  3. For problem areas that are ruled out, disable the corresponding instruments. For example, if analysis shows that the issue is not related to file I/O in a particular storage engine, disable the file I/O instruments for that engine. Then truncate the history and summary tables to remove previously collected events.

  4. Repeat the process at step 1.

    At each iteration, the Performance Schema output, particularly the events_waits_history_long table, will contain less and less noise caused by nonsignificant instruments, and given that this table has a fixed size, will contain more and more data relevant to the analysis of the problem at hand.

    At each iteration, investigation should lead closer and closer to the root cause of the problem, as the signal/noise ratio will improve, making analysis easier.

  5. Once a root cause of performance bottleneck is identified, take the appropriate corrective action, such as:

    • Tune the server parameters (cache sizes, memory, and so forth).

    • Tune a query by writing it differently,

    • Tune the database schema (tables, indexes, and so forth).

    • Tune the code (this applies to storage engine or server developers only).

  6. Start again at step 1, to see the effects of the changes on performance.

The mutex_instances.LOCKED_BY_THREAD_ID and rwlock_instances.WRITE_LOCKED_BY_THREAD_ID columns are extremely important for investigating performance bottlenecks or deadlocks. This is made possible by Performance Schema instrumentation as follows:

  1. Suppose that thread 1 is stuck waiting for a mutex.

  2. You can determine what the thread is waiting for:

    SELECT * FROM events_waits_current WHERE THREAD_ID = thread_1;
    

    Say the query result identifies that the thread is waiting for mutex A, found in events_waits_current.OBJECT_INSTANCE_BEGIN.

  3. You can determine which thread is holding mutex A:

    SELECT * FROM mutex_instances WHERE OBJECT_INSTANCE_BEGIN = mutex_A;
    

    Say the query result identifies that it is thread 2 holding mutex A, as found in mutex_instances.LOCKED_BY_THREAD_ID.

  4. You can see what thread 2 is doing:

    SELECT * FROM events_waits_current WHERE THREAD_ID = thread_2;
    

24.17.1 Query Profiling Using Performance Schema

The following example demonstrates how to use Performance Schema statement events and stage events to retrieve data comparable to profiling information provided by SHOW PROFILES and SHOW PROFILE statements.

As of MySQL 5.7.8, the setup_actors table can be used to limit the collection of historical events by host, user, or account to reduce runtime overhead and the amount of data collected in history tables. The first step of the example shows how to limit collection of historical events to a specific user.

Performance Schema displays event timer information in picoseconds (trillionths of a second) to normalize timing data to a standard unit. In the following example, TIMER_WAIT values are divided by 1000000000000 to show data in units of seconds. Values are also truncated to 6 decimal places to display data in the same format as SHOW PROFILES and SHOW PROFILE statements.

  1. Limit the collection of historical events to the user that will run the query. By default, setup_actors is configured to allow monitoring and historical event collection for all foreground threads:

    mysql> SELECT * FROM setup_actors;
    +------+------+------+---------+---------+
    | HOST | USER | ROLE | ENABLED | HISTORY |
    +------+------+------+---------+---------+
    | %    | %    | %    | YES     | YES     |
    +------+------+------+---------+---------+
    

    Update the default row in the setup_actors table to disable historical event collection and monitoring for all foreground threads, and insert a new row that enables monitoring and historical event collection for the user that will run the query:

    mysql> UPDATE performance_schema.setup_actors SET ENABLED = 'NO', HISTORY = 'NO'
           WHERE HOST = '%' AND USER = '%';
    
    mysql> INSERT INTO performance_schema.setup_actors (HOST,USER,ROLE,ENABLED,HISTORY)
           VALUES('localhost','test_user','%','YES','YES');
    

    Data in the setup_actors table should now appear similar to the following:

    mysql> SELECT * FROM performance_schema.setup_actors;
    +-----------+-----------+------+---------+---------+
    | HOST      | USER      | ROLE | ENABLED | HISTORY |
    +-----------+-----------+------+---------+---------+
    | %         | %         | %    | NO      | NO      |
    | localhost | test_user | %    | YES     | YES     |
    +-----------+-----------+------+---------+---------+
    
  2. Ensure that statement and stage instrumentation is enabled by updating the setup_instruments table. Some instruments may already be enabled by default.

    mysql> UPDATE performance_schema.setup_instruments SET ENABLED = 'YES', TIMED = 'YES'
           WHERE NAME LIKE '%statement/%';
    
    mysql> UPDATE performance_schema.setup_instruments SET ENABLED = 'YES', TIMED = 'YES'
           WHERE NAME LIKE '%stage/%';
    
  3. Ensure that events_statements_* and events_stages_* consumers are enabled. Some consumers may already be enabled by default.

    mysql> UPDATE performance_schema.setup_consumers SET ENABLED = 'YES'
           WHERE NAME LIKE '%events_statements_%';
    
    mysql> UPDATE performance_schema.setup_consumers SET ENABLED = 'YES'
           WHERE NAME LIKE '%events_stages_%';
    
  4. Under the user account you are monitoring, run the statement that you want to profile. For example:

    mysql> SELECT * FROM employees.employees WHERE emp_no = 10001;
    +--------+------------+------------+-----------+--------+------------+
    | emp_no | birth_date | first_name | last_name | gender | hire_date |
    +--------+------------+------------+-----------+--------+------------+
    |  10001 | 1953-09-02 | Georgi     | Facello   | M      | 1986-06-26 |
    +--------+------------+------------+-----------+--------+------------+
    
  5. Identify the EVENT_ID of the statement by querying the events_statements_history_long table. This step is similar to running SHOW PROFILES to identify the Query_ID. The following query produces output similar to SHOW PROFILES:

    mysql> SELECT EVENT_ID, TRUNCATE(TIMER_WAIT/1000000000000,6) as Duration, SQL_TEXT
           FROM performance_schema.events_statements_history_long WHERE SQL_TEXT like '%10001%';
    +----------+----------+--------------------------------------------------------+
    | event_id | duration | sql_text                                               |
    +----------+----------+--------------------------------------------------------+
    |       31 | 0.028310 | SELECT * FROM employees.employees WHERE emp_no = 10001 |
    +----------+----------+--------------------------------------------------------+
    
  6. Query the events_stages_history_long table to retrieve the statement's stage events. Stages are linked to statements using event nesting. Each stage event record has a NESTING_EVENT_ID column that contains the EVENT_ID of the parent statement.

    mysql> SELECT event_name AS Stage, TRUNCATE(TIMER_WAIT/1000000000000,6) AS Duration
           FROM performance_schema.events_stages_history_long WHERE NESTING_EVENT_ID=31;
    +--------------------------------+----------+
    | Stage                          | Duration |
    +--------------------------------+----------+
    | stage/sql/starting             | 0.000080 |
    | stage/sql/checking permissions | 0.000005 |
    | stage/sql/Opening tables       | 0.027759 |
    | stage/sql/init                 | 0.000052 |
    | stage/sql/System lock          | 0.000009 |
    | stage/sql/optimizing           | 0.000006 |
    | stage/sql/statistics           | 0.000082 |
    | stage/sql/preparing            | 0.000008 |
    | stage/sql/executing            | 0.000000 |
    | stage/sql/Sending data         | 0.000017 |
    | stage/sql/end                  | 0.000001 |
    | stage/sql/query end            | 0.000004 |
    | stage/sql/closing tables       | 0.000006 |
    | stage/sql/freeing items        | 0.000272 |
    | stage/sql/cleaning up          | 0.000001 |
    +--------------------------------+----------+
    

24.18 Migrating to Performance Schema System and Status Variable Tables

The INFORMATION_SCHEMA has tables that contain system and status variable information (see Section 23.10, “The INFORMATION_SCHEMA GLOBAL_VARIABLES and SESSION_VARIABLES Tables”, and Section 23.9, “The INFORMATION_SCHEMA GLOBAL_STATUS and SESSION_STATUS Tables”). As of MySQL 5.7.6, the Performance Schema also contains system and status variable tables (see Section 24.10.13, “Performance Schema System Variable Tables”, and Section 24.10.14, “Performance Schema Status Variable Tables”). The Performance Schema tables are intended to replace the INFORMATION_SCHEMA tables, which are deprecated as of MySQL 5.7.6 and will be removed in a future MySQL release.

This section describes the intended migration path away from the INFORMATION_SCHEMA system and status variable tables to the corresponding Performance Schema tables. Application developers should use this information as guidance regarding the changes required to access system and status variables in MySQL 5.7.6 and up as the INFORMATION_SCHEMA tables become deprecated and eventually are removed.

MySQL 5.6

In MySQL 5.6, system and status variable information is available from these SHOW statements:

SHOW VARIABLES
SHOW STATUS

And from these INFORMATION_SCHEMA tables:

INFORMATION_SCHEMA.GLOBAL_VARIABLES
INFORMATION_SCHEMA.SESSION_VARIABLES

INFORMATION_SCHEMA.GLOBAL_STATUS
INFORMATION_SCHEMA.SESSION_STATUS

MySQL 5.7

As of MySQL 5.7.6, the Performance Schema includes these tables as new sources of system and status variable information:

performance_schema.global_variables
performance_schema.session_variables
performance_schema.variables_by_thread

performance_schema.global_status
performance_schema.session_status
performance_schema.status_by_thread
performance_schema.status_by_account
performance_schema.status_by_host
performance_schema.status_by_user

MySQL 5.7.6 also adds a show_compatibility_56 system variable to control how the server makes system and status variable information available.

When show_compatibility_56 is ON, compatibility with MySQL 5.6 is enabled. The older system and status variable sources (SHOW statements, INFORMATION_SCHEMA tables) are available with semantics identical to MySQL 5.6. Applications should run as is, with no code changes, and should see the same variable names and values as in MySQL 5.6. Warnings occur under these circumstances:

  • A deprecation warning is raised when selecting from the INFORMATION_SCHEMA tables.

  • In MySQL 5.7.6 and 5.7.7, a deprecation warning is raised when using a WHERE clause with the SHOW statements. This behavior does not occur as of MySQL 5.7.8.

When show_compatibility_56 is OFF, compatibility with MySQL 5.6 is disabled and several changes result. Applications must be revised as follows to run properly:

  • Selecting from the INFORMATION_SCHEMA tables produces an error. Applications that access the INFORMATION_SCHEMA tables should be revised to use the corresponding Performance Schema tables instead.

    Before MySQL 5.7.9, selecting from the INFORMATION_SCHEMA tables produces an empty result set plus a deprecation warning. This was not sufficient notice to signal the need to migrate to the corresponding Performance Schema system and status variable tables for the case that show_compatibility_56=OFF. Producing an error in MySQL 5.7.9 and higher makes it more evident that an application is operating under conditions that require modification, as well as where the problem lies.

    In MySQL 5.7.6 and 5.7.7, the Performance Schema session_variables and session_status tables do not fully reflect all variable values in effect for the current session; they include no rows for global variables that have no session counterpart. This is corrected in MySQL 5.7.8.

  • Output for the SHOW statements is produced using the underlying Performance Schema tables. Applications written to use these statements can still use them, but it is best to use MySQL 5.7.8 or higher. In MySQL 5.7.6 and 5.7.7, the results may differ:

    • SHOW [SESSION] VARIABLES output does not include global variables that have no session counterpart.

    • Using a WHERE clause with the SHOW statements produces an error.

  • These Slave_xxx status variables become unavailable through SHOW STATUS:

    Slave_heartbeat_period
    Slave_last_heartbeat
    Slave_received_heartbeats
    Slave_retried_transactions
    Slave_running
    

    Applications that use these status variables should be revised to obtain this information using the replication-related Performance Schema tables. For details, see Effect of show_compatibility_56 on Slave Status Variables.

Migration and Privileges

Initially, with the introduction of Performance Schema system and status variable tables in MySQL 5.7.6, access to those tables required the SELECT privilege, just as for other Performance Schema tables. However, this had the consequence that when show_compatibility_56=OFF, the SHOW VARIABLES and SHOW STATUS statements also required the SELECT privilege: With compatibility disabled, output for those statements was taken from the Performance Schema global_variables, session_variables, global_status, and session_status tables.

As of MySQL 5.7.9, those Performance Schema tables are world readable and accessible without the SELECT privilege. Consequently, SHOW VARIABLES and SHOW STATUS do not require privileges on the underlying Performance Schema tables from which their output is produced when show_compatibility_56=OFF.

Beyond MySQL 5.7

In a MySQL 8.0, the INFORMATION_SCHEMA variable tables and the show_compatibility_56 system variable are removed, and output from the SHOW statements is always based on the underlying Performance Schema tables.

Applications that have been revised to work in MySQL 5.7 when show_compatibility_56=OFF should work without further changes, except that it will not be possible to test or set show_compatibility_56 because it will not exist.