Chapter 18 Replication

Replication enables data from one MySQL database server (the master) to be copied to one or more MySQL database servers (the slaves). Replication is asynchronous by default; slaves do not need to be connected permanently to receive updates from the master. Depending on the configuration, you can replicate all databases, selected databases, or even selected tables within a database.

Advantages of replication in MySQL include:

  • Scale-out solutions - spreading the load among multiple slaves to improve performance. In this environment, all writes and updates must take place on the master server. Reads, however, may take place on one or more slaves. This model can improve the performance of writes (since the master is dedicated to updates), while dramatically increasing read speed across an increasing number of slaves.

  • Data security - because data is replicated to the slave, and the slave can pause the replication process, it is possible to run backup services on the slave without corrupting the corresponding master data.

  • Analytics - live data can be created on the master, while the analysis of the information can take place on the slave without affecting the performance of the master.

  • Long-distance data distribution - you can use replication to create a local copy of data for a remote site to use, without permanent access to the master.

For information on how to use replication in such scenarios, see Section 18.3, “Replication Solutions”.

MySQL 5.7 supports different methods of replication. The traditional method is based on replicating events from the master's binary log, and requires the log files and positions in them to be synchronized between master and slave. The newer method based on global transaction identifiers (GTIDs) is transactional and therefore does not require working with log files or positions within these files, which greatly simplifies many common replication tasks. Replication using GTIDs guarantees consistency between master and slave as long as all transactions committed on the master have also been applied on the slave. For more information about GTIDs and GTID-based replication in MySQL, see Section 18.1.3, “Replication with Global Transaction Identifiers”. For information on using binary log file position based replication, see Section 18.1, “Configuring Replication”.

Replication in MySQL supports different types of synchronization. The original type of synchronization is one-way, asynchronous replication, in which one server acts as the master, while one or more other servers act as slaves. This is in contrast to the synchronous replication which is a characteristic of MySQL Cluster (see Chapter 20, MySQL NDB Cluster 7.5). In MySQL 5.7, semisynchronous replication is supported in addition to the built-in asynchronous replication. With semisynchronous replication, a commit performed on the master blocks before returning to the session that performed the transaction until at least one slave acknowledges that it has received and logged the events for the transaction; see Section 18.3.9, “Semisynchronous Replication”. MySQL 5.7 also supports delayed replication such that a slave server deliberately lags behind the master by at least a specified amount of time; see Section 18.3.10, “Delayed Replication”. For scenarios where synchronous replication is required, use MySQL Cluster (see Chapter 20, MySQL NDB Cluster 7.5).

There are a number of solutions available for setting up replication between servers, and the best method to use depends on the presence of data and the engine types you are using. For more information on the available options, see Section 18.1.2, “Setting Up Binary Log File Position Based Replication”.

There are two core types of replication format, Statement Based Replication (SBR), which replicates entire SQL statements, and Row Based Replication (RBR), which replicates only the changed rows. You can also use a third variety, Mixed Based Replication (MBR). For more information on the different replication formats, see Section 18.2.1, “Replication Formats”.

Replication is controlled through a number of different options and variables. For more information, see Section 18.1.6, “Replication and Binary Logging Options and Variables”.

You can use replication to solve a number of different problems, including performance, supporting the backup of different databases, and as part of a larger solution to alleviate system failures. For information on how to address these issues, see Section 18.3, “Replication Solutions”.

For notes and tips on how different data types and statements are treated during replication, including details of replication features, version compatibility, upgrades, and potential problems and their resolution, see Section 18.4, “Replication Notes and Tips”. For answers to some questions often asked by those who are new to MySQL Replication, see Section A.13, “MySQL 5.7 FAQ: Replication”.

For detailed information on the implementation of replication, how replication works, the process and contents of the binary log, background threads and the rules used to decide how statements are recorded and replicated, see Section 18.2, “Replication Implementation”.

18.1 Configuring Replication

This section describes how to configure the different types of replication available in MySQL and includes the setup and configuration required for a replication environment, including step-by-step instructions for creating a new replication environment. The major components of this section are:

18.1.1 Binary Log File Position Based Replication Configuration Overview

This section describes replication between MySQL servers based on the binary log file position method, where the MySQL instance operating as the master (the source of the database changes) writes updates and changes as events to the binary log. The information in the binary log is stored in different logging formats according to the database changes being recorded. Slaves are configured to read the binary log from the master and to execute the events in the binary log on the slave's local database.

Each slave receives a copy of the entire contents of the binary log. It is the responsibility of the slave to decide which statements in the binary log should be executed. Unless you specify otherwise, all events in the master binary log are executed on the slave. If required, you can configure the slave to process only events that apply to particular databases or tables.

Important

You cannot configure the master to log only certain events.

Each slave keeps a record of the binary log coordinates: the file name and position within the file that it has read and processed from the master. This means that multiple slaves can be connected to the master and executing different parts of the same binary log. Because the slaves control this process, individual slaves can be connected and disconnected from the server without affecting the master's operation. Also, because each slave records the current position within the binary log, it is possible for slaves to be disconnected, reconnect and then resume processing.

The master and each slave must be configured with a unique ID (using the server-id option). In addition, each slave must be configured with information about the master host name, log file name, and position within that file. These details can be controlled from within a MySQL session using the CHANGE MASTER TO statement on the slave. The details are stored within the slave's master info repository, which can be either a file or a table (see Section 18.2.4, “Replication Relay and Status Logs”).

18.1.2 Setting Up Binary Log File Position Based Replication

This section describes how to set up a MySQL server to use binary log file position based replication. There are a number of different methods for setting up replication, and the exact method to use depends on how you are setting up replication, and whether you already have data within your master database.

There are some generic tasks that are common to all setups:

Note

Certain steps within the setup process require the SUPER privilege. If you do not have this privilege, it might not be possible to enable replication.

After configuring the basic options, select your scenario:

Before administering MySQL replication servers, read this entire chapter and try all statements mentioned in Section 14.4.1, “SQL Statements for Controlling Master Servers”, and Section 14.4.2, “SQL Statements for Controlling Slave Servers”. Also familiarize yourself with the replication startup options described in Section 18.1.6, “Replication and Binary Logging Options and Variables”.

18.1.2.1 Setting the Replication Master Configuration

To configure a master to use binary log file position based replication, you must enable binary logging and establish a unique server ID. If this has not already been done, a server restart is required.

Binary logging must be enabled on the master because the binary log is the basis for replicating changes from the master to its slaves. If binary logging is not enabled on the master using the log-bin option, replication is not possible.

Each server within a replication group must be configured with a unique server ID. This ID is used to identify individual servers within the group, and must be a positive integer between 1 and (232)−1. How you organize and select the numbers is your choice.

To configure the binary log and server ID options, shut down the MySQL server and edit the my.cnf or my.ini file. Within the [mysqld] section of the configuration file, add the log-bin and server-id options. If these options already exist, but are commented out, uncomment the options and alter them according to your needs. For example, to enable binary logging using a log file name prefix of mysql-bin, and configure a server ID of 1, use these lines:

[mysqld]
log-bin=mysql-bin
server-id=1

After making the changes, restart the server.

Note

The following options have an impact on this procedure:

  • if you omit server-id (or set it explicitly to its default value of 0), the master refuses any connections from slaves.

  • For the greatest possible durability and consistency in a replication setup using InnoDB with transactions, you should use innodb_flush_log_at_trx_commit=1 and sync_binlog=1 in the master my.cnf file.

  • Ensure that the skip-networking option is not enabled on your replication master. If networking has been disabled, the slave cannot communicate with the master and replication fails.

18.1.2.2 Creating a User for Replication

Each slave connects to the master using a MySQL user name and password, so there must be a user account on the master that the slave can use to connect. Any account can be used for this operation, providing it has been granted the REPLICATION SLAVE privilege. You can choose to create a different account for each slave, or connect to the master using the same account for each slave.

Although you do not have to create an account specifically for replication, you should be aware that the replication user name and password are stored in plain text in the master info repository file or table (see Section 18.2.4.2, “Slave Status Logs”). Therefore, you may want to create a separate account that has privileges only for the replication process, to minimize the possibility of compromise to other accounts.

To create a new account, use CREATE USER. To grant this account the privileges required for replication, use the GRANT statement. If you create an account solely for the purposes of replication, that account needs only the REPLICATION SLAVE privilege. For example, to set up a new user, repl, that can connect for replication from any host within the mydomain.com domain, issue these statements on the master:

mysql> CREATE USER 'repl'@'%.mydomain.com' IDENTIFIED BY 'slavepass';
mysql> GRANT REPLICATION SLAVE ON *.* TO 'repl'@'%.mydomain.com';

See Section 14.7.1, “Account Management Statements”, for more information on statements for manipulation of user accounts.

18.1.2.3 Obtaining the Replication Master Binary Log Coordinates

To configure the slave to start the replication process at the correct point, you need the master's current coordinates within its binary log.

If the master has been running previously without binary logging enabled, the log file name and position values displayed by SHOW MASTER STATUS or mysqldump --master-data are empty. In that case, the values that you need to use later when specifying the slave's log file and position are the empty string ('') and 4.

If the master has been binary logging previously, use this procedure to obtain the master binary log coordinates:

Warning

This procedure uses FLUSH TABLES WITH READ LOCK, which blocks COMMIT operations for InnoDB tables.

  1. Start a session on the master by connecting to it with the command-line client, and flush all tables and block write statements by executing the FLUSH TABLES WITH READ LOCK statement:

    mysql> FLUSH TABLES WITH READ LOCK;
    
    Warning

    Leave the client from which you issued the FLUSH TABLES statement running so that the read lock remains in effect. If you exit the client, the lock is released.

  2. In a different session on the master, use the SHOW MASTER STATUS statement to determine the current binary log file name and position:

    mysql > SHOW MASTER STATUS;
    +------------------+----------+--------------+------------------+
    | File             | Position | Binlog_Do_DB | Binlog_Ignore_DB |
    +------------------+----------+--------------+------------------+
    | mysql-bin.000003 | 73       | test         | manual,mysql     |
    +------------------+----------+--------------+------------------+
    

    The File column shows the name of the log file and the Position column shows the position within the file. In this example, the binary log file is mysql-bin.000003 and the position is 73. Record these values. You need them later when you are setting up the slave. They represent the replication coordinates at which the slave should begin processing new updates from the master.

You now have the information you need to enable the slave to start reading from the binary log in the correct place to start replication.

The next step depends on whether you have existing data on the master. Choose one of the following options:

18.1.2.4 Choosing a Method for Data Snapshots

If the master database contains existing data it is necessary to copy this data to each slave. There are different ways to dump the data from the master database. The following sections describe possible options.

To select the appropriate method of dumping the database, choose between these options:

  • Use the mysqldump tool to create a dump of all the databases you want to replicate. This is the recommended method, especially when using InnoDB.

  • If your database is stored in binary portable files, you can copy the raw data files to a slave. This can be more efficient than using mysqldump and importing the file on each slave, because it skips the overhead of updating indexes as the INSERT statements are replayed. With storage engines such as InnoDB this is not recommended.

18.1.2.4.1 Creating a Data Snapshot Using mysqldump

To create a snapshot of the data in an existing master database, use the mysqldump tool. Once the data dump has been completed, import this data into the slave before starting the replication process.

The following example dumps all databases to a file named dbdump.db, and includes the --master-data option which automatically appends the CHANGE MASTER TO statement required on the slave to start the replication process:

shell> mysqldump --all-databases --master-data > dbdump.db
Note

If you do not use --master-data, then it is necessary to lock all tables in a separate session manually. See Section 18.1.2.3, “Obtaining the Replication Master Binary Log Coordinates”.

It is possible to exclude certain databases from the dump using the mysqldump tool. If you want to choose which databases to include in the dump, do not use --all-databases. Choose one of these options:

  • Exclude all the tables in the database using --ignore-table option.

  • Name only those databases which you want dumped using the --databases option.

For more information, see Section 5.5.4, “mysqldump — A Database Backup Program”.

To import the data, either copy the dump file to the slave, or access the file from the master when connecting remotely to the slave.

18.1.2.4.2 Creating a Data Snapshot Using Raw Data Files

This section describes how to create a data snapshot using the raw files which make up the database. Employing this method with a table using a storage engine that has complex caching or logging algorithms requires extra steps to produce a perfect point in time snapshot: the initial copy command could leave out cache information and logging updates, even if you have acquired a global read lock. How the storage engine responds to this depends on its crash recovery abilities.

If you use InnoDB tables, you can use the mysqlbackup command from the MySQL Enterprise Backup component to produce a consistent snapshot. This command records the log name and offset corresponding to the snapshot to be used on the slave. MySQL Enterprise Backup is a commercial product that is included as part of a MySQL Enterprise subscription. See Section 28.2, “MySQL Enterprise Backup Overview” for detailed information.

This method also does not work reliably if the master and slave have different values for ft_stopword_file, ft_min_word_len, or ft_max_word_len and you are copying tables having full-text indexes.

Assuming the above exceptions do not apply to your database, use the cold backup technique to obtain a reliable binary snapshot of InnoDB tables: do a slow shutdown of the MySQL Server, then copy the data files manually.

To create a raw data snapshot of MyISAM tables when your MySQL data files exist on a single file system, you can use standard file copy tools such as cp or copy, a remote copy tool such as scp or rsync, an archiving tool such as zip or tar, or a file system snapshot tool such as dump. If you are replicating only certain databases, copy only those files that relate to those tables. For InnoDB, all tables in all databases are stored in the system tablespace files, unless you have the innodb_file_per_table option enabled.

The following files are not required for replication:

Depending on whether you are using InnoDB tables or not, choose one of the following:

If you are using InnoDB tables, and also to get the most consistent results with a raw data snapshot, shut down the master server during the process, as follows:

  1. Acquire a read lock and get the master's status. See Section 18.1.2.3, “Obtaining the Replication Master Binary Log Coordinates”.

  2. In a separate session, shut down the master server:

    shell> mysqladmin shutdown
    
  3. Make a copy of the MySQL data files. The following examples show common ways to do this. You need to choose only one of them:

    shell> tar cf /tmp/db.tar ./data
    shell> zip -r /tmp/db.zip ./data
    shell> rsync --recursive ./data /tmp/dbdata
    
  4. Restart the master server.

If you are not using InnoDB tables, you can get a snapshot of the system from a master without shutting down the server as described in the following steps:

  1. Acquire a read lock and get the master's status. See Section 18.1.2.3, “Obtaining the Replication Master Binary Log Coordinates”.

  2. Make a copy of the MySQL data files. The following examples show common ways to do this. You need to choose only one of them:

    shell> tar cf /tmp/db.tar ./data
    shell> zip -r /tmp/db.zip ./data
    shell> rsync --recursive ./data /tmp/dbdata
    
  3. In the client where you acquired the read lock, release the lock:

    mysql> UNLOCK TABLES;
    

Once you have created the archive or copy of the database, copy the files to each slave before starting the slave replication process.

18.1.2.5 Setting Up Replication Slaves

The following sections describe how to set up slaves. Before you proceed, ensure that you have:

18.1.2.5.1 Setting the Replication Slave Configuration

Each replication slave must have a unique server ID. If this has not already been done, this part of slave setup requires a server restart.

If the slave server ID is not already set, or the current value conflicts with the value that you have chosen for the master server, shut down the slave server and edit the [mysqld] section of the configuration file to specify a unique server ID. For example:

[mysqld]
server-id=2

After making the changes, restart the server.

If you are setting up multiple slaves, each one must have a unique server-id value that differs from that of the master and from any of the other slaves.

Note

If you omit server-id (or set it explicitly to its default value of 0), the slave refuses to connect to a master.

You do not have to enable binary logging on the slave for replication to be set up. However, if you enable binary logging on the slave, you can use the slave's binary log for data backups and crash recovery, and also use the slave as part of a more complex replication topology. For example, where this slave then acts as a master to other slaves.

18.1.2.5.2 Setting the Master Configuration on the Slave

To set up the slave to communicate with the master for replication, configure the slave with the necessary connection information. To do this, execute the following statement on the slave, replacing the option values with the actual values relevant to your system:

mysql> CHANGE MASTER TO
    ->     MASTER_HOST='master_host_name',
    ->     MASTER_USER='replication_user_name',
    ->     MASTER_PASSWORD='replication_password',
    ->     MASTER_LOG_FILE='recorded_log_file_name',
    ->     MASTER_LOG_POS=recorded_log_position;
Note

Replication cannot use Unix socket files. You must be able to connect to the master MySQL server using TCP/IP.

The CHANGE MASTER TO statement has other options as well. For example, it is possible to set up secure replication using SSL. For a full list of options, and information about the maximum permissible length for the string-valued options, see Section 14.4.2.1, “CHANGE MASTER TO Syntax”.

The next steps depend on whether you have existing data to import to the slave or not. See Section 18.1.2.4, “Choosing a Method for Data Snapshots” for more information. Choose one of the following:

18.1.2.5.3 Setting Up Replication between a New Master and Slaves

When there is no snapshot of a previous database to import, configure the slave to start the replication from the new master.

To set up replication between a master and a new slave:

  1. Start up the MySQL slave and connect to it.

  2. Execute a CHANGE MASTER TO statement to set the master replication server configuration. See Section 18.1.2.5.2, “Setting the Master Configuration on the Slave”.

Perform these slave setup steps on each slave.

This method can also be used if you are setting up new servers but have an existing dump of the databases from a different server that you want to load into your replication configuration. By loading the data into a new master, the data is automatically replicated to the slaves.

If you are setting up a new replication environment using the data from a different existing database server to create a new master, run the dump file generated from that server on the new master. The database updates are automatically propagated to the slaves:

shell> mysql -h master < fulldb.dump
18.1.2.5.4 Setting Up Replication with Existing Data

When setting up replication with existing data, transfer the snapshot from the master to the slave before starting replication. The process for importing data to the slave depends on how you created the snapshot of data on the master.

Choose one of the following:

If you used mysqldump:

  1. Start the slave, using the --skip-slave-start option so that replication does not start.

  2. Import the dump file:

    shell> mysql < fulldb.dump
    

If you created a snapshot using the raw data files:

  1. Extract the data files into your slave data directory. For example:

    shell> tar xvf dbdump.tar
    

    You may need to set permissions and ownership on the files so that the slave server can access and modify them.

  2. Start the slave, using the --skip-slave-start option so that replication does not start.

  3. Configure the slave with the replication coordinates from the master. This tells the slave the binary log file and position within the file where replication needs to start. Also, configure the slave with the login credentials and host name of the master. For more information on the CHANGE MASTER TO statement required, see Section 18.1.2.5.2, “Setting the Master Configuration on the Slave”.

  4. Start the slave threads:

    mysql> START SLAVE;
    

After you have performed this procedure, the slave connects to the master and replicates any updates that have occurred on the master since the snapshot was taken.

If the server-id option for the master is not correctly set, slaves cannot connect to it. Similarly, if you have not set the server-id option correctly for the slave, you get the following error in the slave's error log:

Warning: You should set server-id to a non-0 value if master_host
is set; we will force server id to 2, but this MySQL server will
not act as a slave.

You also find error messages in the slave's error log if it is not able to replicate for any other reason.

The slave stores information about the master you have configured in its master info repository. The master info repository can be in the form of files or a table, as determined by the value set for --master-info-repository. When a slave uses --master-info-repository=FILE, two files are stored in the data directory, named master.info and relay-log.info. If --master-info-repository=TABLE instead, this information is saved in the master_slave_info table in the mysql database. In either case, do not remove or edit the files or table. Always use the CHANGE MASTER TO statement to change replication parameters. The slave can use the values specified in the statement to update the status files automatically. See Section 18.2.4, “Replication Relay and Status Logs”, for more information.

Note

The contents of the master info repository override some of the server options specified on the command line or in my.cnf. See Section 18.1.6, “Replication and Binary Logging Options and Variables”, for more details.

A single snapshot of the master suffices for multiple slaves. To set up additional slaves, use the same master snapshot and follow the slave portion of the procedure just described.

18.1.2.6 Adding Slaves to a Replication Environment

You can add another slave to an existing replication configuration without stopping the master. Instead, set up the new slave by making a copy of an existing slave, except that you configure the new slave with a different server-id value.

To duplicate an existing slave:

  1. Shut down the existing slave:

    shell> mysqladmin shutdown
    
  2. Copy the data directory from the existing slave to the new slave. You can do this by creating an archive using tar or WinZip, or by performing a direct copy using a tool such as cp or rsync. Ensure that you also copy the log files and relay log files.

    A common problem that is encountered when adding new replication slaves is that the new slave fails with a series of warning and error messages like these:

    071118 16:44:10 [Warning] Neither --relay-log nor --relay-log-index were used; so
    replication may break when this MySQL server acts as a slave and has his hostname
    changed!! Please use '--relay-log=new_slave_hostname-relay-bin' to avoid this problem.
    071118 16:44:10 [ERROR] Failed to open the relay log './old_slave_hostname-relay-bin.003525'
    (relay_log_pos 22940879)
    071118 16:44:10 [ERROR] Could not find target log during relay log initialization
    071118 16:44:10 [ERROR] Failed to initialize the master info structure
    

    This situation can occur if the --relay-log option is not specified, as the relay log files contain the host name as part of their file names. This is also true of the relay log index file if the --relay-log-index option is not used. See Section 18.1.6, “Replication and Binary Logging Options and Variables”, for more information about these options.

    To avoid this problem, use the same value for --relay-log on the new slave that was used on the existing slave. If this option was not set explicitly on the existing slave, use existing_slave_hostname-relay-bin. If this is not possible, copy the existing slave's relay log index file to the new slave and set the --relay-log-index option on the new slave to match what was used on the existing slave. If this option was not set explicitly on the existing slave, use existing_slave_hostname-relay-bin.index. Alternatively, if you have already tried to start the new slave after following the remaining steps in this section and have encountered errors like those described previously, then perform the following steps:

    1. If you have not already done so, issue a STOP SLAVE on the new slave.

      If you have already started the existing slave again, issue a STOP SLAVE on the existing slave as well.

    2. Copy the contents of the existing slave's relay log index file into the new slave's relay log index file, making sure to overwrite any content already in the file.

    3. Proceed with the remaining steps in this section.

  3. Copy the master info and relay log info repositories (see Section 18.2.4, “Replication Relay and Status Logs”) from the existing slave to the new slave. These hold the current log coordinates for the master's binary log and the slave's relay log.

  4. Start the existing slave.

  5. On the new slave, edit the configuration and give the new slave a unique server-id not used by the master or any of the existing slaves.

  6. Start the new slave. The slave uses the information in its master info repository to start the replication process.

18.1.3 Replication with Global Transaction Identifiers

This section explains transaction-based replication using global transaction identifiers (GTIDs). When using GTIDs, each transaction can be identified and tracked as it is committed on the originating server and applied by any slaves; this means that it is not necessary when using GTIDs to refer to log files or positions within those files when starting a new slave or failing over to a new master, which greatly simplifies these tasks. Because GTID-based replication is completely transaction-based, it is simple to determine whether masters and slaves are consistent; as long as all transactions committed on a master are also committed on a slave, consistency between the two is guaranteed. You can use either statement-based or row-based replication with GTIDs (see Section 18.2.1, “Replication Formats”); however, for best results, we recommend that you use the row-based format.

This section discusses the following topics:

For information about MySQL Server options and variables relating to GTID-based replication, see Section 18.1.6.5, “Global Transaction ID Options and Variables”. See also Section 13.17, “Functions Used with Global Transaction IDs”, which describes SQL functions supported by MySQL 5.7 for use with GTIDs.

18.1.3.1 GTID Concepts

A global transaction identifier (GTID) is a unique identifier created and associated with each transaction committed on the server of origin (master). This identifier is unique not only to the server on which it originated, but is unique across all servers in a given replication setup. There is a 1-to-1 mapping between all transactions and all GTIDs.

The following paragraphs provide a basic description of GTIDs. More advanced concepts are covered later in the following sections:

A GTID is represented as a pair of coordinates, separated by a colon character (:), as shown here:

GTID = source_id:transaction_id

The source_id identifies the originating server. Normally, the server's server_uuid is used for this purpose. The transaction_id is a sequence number determined by the order in which the transaction was committed on this server; for example, the first transaction to be committed has 1 as its transaction_id, and the tenth transaction to be committed on the same originating server is assigned a transaction_id of 10. It is not possible for a transaction to have 0 as a sequence number in a GTID. For example, the twenty-third transaction to be committed originally on the server with the UUID 3E11FA47-71CA-11E1-9E33-C80AA9429562 has this GTID:

3E11FA47-71CA-11E1-9E33-C80AA9429562:23

This format is used to represent GTIDs in the output of statements such as SHOW SLAVE STATUS as well as in the binary log. They can also be seen when viewing the log file with mysqlbinlog --base64-output=DECODE-ROWS or in the output from SHOW BINLOG EVENTS.

As written in the output of statements such as SHOW MASTER STATUS or SHOW SLAVE STATUS, a sequence of GTIDs originating from the same server may be collapsed into a single expression, as shown here.

3E11FA47-71CA-11E1-9E33-C80AA9429562:1-5

The example just shown represents the first through fifth transactions originating on the MySQL Server whose server_uuid is 3E11FA47-71CA-11E1-9E33-C80AA9429562.

This format is also used to supply the argument required by the START SLAVE options SQL_BEFORE_GTIDS and SQL_AFTER_GTIDS.

GTID Sets

A GTID set is a set of global transaction identifiers which is represented as shown here:

gtid_set:
    uuid_set [, uuid_set] ...
    | ''

uuid_set:
    uuid:interval[:interval]...

uuid:
    hhhhhhhh-hhhh-hhhh-hhhh-hhhhhhhhhhhh

h:
    [0-9|A-F]

interval:
    n[-n]

    (n >= 1)

GTID sets are used in the MySQL Server in several ways. For example, the values stored by the gtid_executed and gtid_purged system variables are represented as GTID sets. In addition, the functions GTID_SUBSET() and GTID_SUBTRACT() require GTID sets as input. When GTID sets are returned from server variables, UUIDs are in alphabetical order and numeric intervals are merged and in ascending order.

GTIDs are always preserved between master and slave. This means that you can always determine the source for any transaction applied on any slave by examining its binary log. In addition, once a transaction with a given GTID is committed on a given server, any subsequent transaction having the same GTID is ignored by that server. Thus, a transaction committed on the master can be applied no more than once on the slave, which helps to guarantee consistency.

When GTIDs are in use, the slave has no need for any nonlocal data, such as the name of a file on the master and a position within that file. All necessary information for synchronizing with the master is obtained directly from the replication data stream. GTIDs replace the file-offset pairs previously required to determine points for starting, stopping, or resuming the flow of data between master and slave. therefore, do not include MASTER_LOG_FILE or MASTER_LOG_POS options in the CHANGE MASTER TO statement used to direct a slave to replicate from a given master; instead it is necessary only to enable the MASTER_AUTO_POSITION option. For the exact steps needed to configure and start masters and slaves using GTID-based replication, see Section 18.1.3.2, “Setting Up Replication Using GTIDs”.

The generation and life cycle of a GTID consist of the following steps:

  1. A transaction is executed and committed on the master.

    This transaction is assigned a GTID using the master's UUID and the smallest nonzero transaction sequence number not yet used on this server; the GTID is written to the master's binary log (immediately preceding the transaction itself in the log).

  2. After the binary log data is transmitted to the slave and stored in the slave's relay log (using established mechanisms for this process—see Section 18.2, “Replication Implementation”, for details), the slave reads the GTID and sets the value of its gtid_next system variable as this GTID. This tells the slave that the next transaction must be logged using this GTID.

    It is important to note that the slave sets gtid_next in a session context.

  3. The slave verifies that this GTID has not already been used to log a transaction in its own binary log. If this GTID has not been used, the slave then writes the GTID, applies the transaction, and writes the transaction to its binary log. By reading and checking the transaction's GTID first, before processing the transaction itself, the slave guarantees not only that no previous transaction having this GTID has been applied on the slave, but also that no other session has already read this GTID but has not yet committed the associated transaction. In other words, multiple clients are not permitted to apply the same transaction concurrently.

  4. Because gtid_next is not empty, the slave does not attempt to generate a GTID for this transaction but instead writes the GTID stored in this variable—that is, the GTID obtained from the master—immediately preceding the transaction in its binary log.

mysql.gtid_executed Table

Beginning with MySQL 5.7.5, GTIDs are stored in a table named gtid_executed, in the mysql database. A row in this table contains, for each GTID or set of GTIDs that it represents, the UUID of the originating server, and the starting and ending transaction IDs of the set; for a row referencing only a single GTID, these last two values are the same.

The mysql.gtid_executed table is created (if it does not already exist) when the MySQL Server is installed or upgraded, using a CREATE TABLE statement similar to that shown here:

CREATE TABLE gtid_executed (
    source_uuid CHAR(36) NOT NULL,
    interval_start BIGINT(20) NOT NULL,
    interval_end BIGINT(20) NOT NULL,                                                                                                                                                                                  
    PRIMARY KEY (source_uuid, interval_start)
)      
Warning

As with other MySQL system tables, do not attempt to create or modify this table yourself.

GTIDs are stored in the mysql.gtid_executed table only when gtid_mode is ON or ON_PERMISSIVE. GTIDs are stored in this table without regard to whether binary logging is enabled. However, the manner in which they are stored differs depending on whether log_bin is ON or OFF:

  • If binary logging is disabled (log_bin is OFF), the server stores the GTID belonging to each transaction together with the transaction in the table.

    In addition, when binary logging is disabled, this table is compressed periodically at a user-configurable rate; see mysql.gtid_executed Table Compression, for more information.

  • If binary logging is enabled (log_bin is ON), then in addition to storing the GTIDs in mysql.gtid_executed, whenever the binary log is rotated or the server is shut down, the server writes GTIDs for all transactions that were written into the previous binary log into the new binary log.

    In the event of the server stopping unexpectedly, the set of GTIDs from the previous binary log is not saved in the mysql.gtid_executed table. In this case, these GTIDs are added to the table and to the set of GTIDs in the gtid_executed system variable during recovery.

The mysql.gtid_executed table is reset by RESET MASTER.

mysql.gtid_executed Table Compression

Over the course of time, the mysql.gtid_executed table can become filled with many rows referring to individual GTIDs that originate on the same server, and whose transaction IDs make up a sequence, similar to what is shown here:

mysql> SELECT * FROM mysql.gtid_executed;
+--------------------------------------+----------------+--------------+
| source_uuid                          | interval_start | interval_end |
|--------------------------------------+----------------+--------------|
| 3E11FA47-71CA-11E1-9E33-C80AA9429562 | 37             | 37           |
| 3E11FA47-71CA-11E1-9E33-C80AA9429562 | 38             | 38           |
| 3E11FA47-71CA-11E1-9E33-C80AA9429562 | 39             | 39           |
| 3E11FA47-71CA-11E1-9E33-C80AA9429562 | 40             | 40           |
| 3E11FA47-71CA-11E1-9E33-C80AA9429562 | 41             | 41           |
| 3E11FA47-71CA-11E1-9E33-C80AA9429562 | 42             | 42           |
| 3E11FA47-71CA-11E1-9E33-C80AA9429562 | 43             | 43           |
...

Considerable space can be saved if this table is compressed periodically by replacing each such set of rows with a single row that spans the entire interval of transaction identifiers, like this:

+--------------------------------------+----------------+--------------+
| source_uuid                          | interval_start | interval_end |
|--------------------------------------+----------------+--------------|
| 3E11FA47-71CA-11E1-9E33-C80AA9429562 | 37             | 43           |
...

When GTIDs are enabled, the server performs this type of compression on the mysql.gtid_executed table periodically. You can control the number of transactions that are allowed to elapse before the table is compressed, and thus the compression rate, by setting the executed_gtids_compression_period system variable. This variable's default value is 1000; this means that, by default, compression of the table is performed after each 1000 transactions. Setting executed_gtid_compression_period to 0 prevents the compression from being performed at all; however, you should be prepared for a potentially large increase in the amount of disk space that may be required by the gtid_executed table if you do this.

Note

When binary logging is enabled, the value of executed_gtids_compression_period is not used and the mysql.gtid_executed table is compressed on each binary log rotation.

Compression of the mysql.gtid_executed table is performed by a dedicated foreground thread that is created whenever GTIDs are enabled on the server. This thread is not listed in the output of SHOW PROCESSLIST, but it can be viewed as a row in the threads table, as shown here:

mysql> SELECT * FROM PERFORMANCE_SCHEMA.THREADS WHERE NAME LIKE '%gtid%'\G
*************************** 1. row ***************************
          THREAD_ID: 21
               NAME: thread/sql/compress_gtid_table
               TYPE: FOREGROUND
     PROCESSLIST_ID: 139635685943104
   PROCESSLIST_USER: NULL
   PROCESSLIST_HOST: NULL
     PROCESSLIST_DB: NULL
PROCESSLIST_COMMAND: Daemon
   PROCESSLIST_TIME: 611
  PROCESSLIST_STATE: Suspending
   PROCESSLIST_INFO: NULL
   PARENT_THREAD_ID: 1
               ROLE: NULL
       INSTRUMENTED: YES

This thread has the name thread/sql/compress_gtid_table, and normally sleeps until executed_gtids_compression_period transactions have been executed, then wakes up to perform compression of the mysql.gtid_executed table as described previously. It then sleeps until another executed_gtids_compression_period transactions have taken place, then wakes up to perform the compression again, repeating this loop indefinitely. Setting this value to 0 when binary logging is disabled means that the thread always sleeps and never wakes up.

18.1.3.2 Setting Up Replication Using GTIDs

This section describes a process for configuring and starting GTID-based replication in MySQL 5.7. This is a cold start procedure that assumes either that you are starting the replication master for the first time, or that it is possible to stop it; for information about provisioning replication slaves using GTIDs from a running master, see Section 18.1.3.3, “Using GTIDs for Failover and Scaleout”. For information about changing GTID mode on servers online, see Section 18.1.5, “Changing Replication Modes on Online Servers”.

The key steps in this startup process for the simplest possible GTID replication topology—consisting of one master and one slave—are as follows:

  1. If replication is already running, synchronize both servers by making them read-only.

  2. Stop both servers.

  3. Restart both servers with GTIDs enabled and the correct options configured.

    The mysqld options necessary to start the servers as described are discussed in the example that follows later in this section.

    Note

    server_uuid must exist for GTIDs to function correctly.

  4. Instruct the slave to use the master as the replication data source and to use auto-positioning, and then start the slave.

    The SQL statements needed to accomplish this step are described in the example that follows later in this section.

  5. Enable read mode again on both servers, so that they can accept updates.

In the following example, two servers are already running as master and slave, using MySQL's binary log position-based replication protocol. If you are starting with new servers, see Section 18.1.2.2, “Creating a User for Replication” for information about adding a specific user for replication connections and Section 18.1.2.1, “Setting the Replication Master Configuration” for information about setting the server-id. The following examples show how to use startup options when running mysqld. Alternatively you can store startup options in an option file, see Section 5.2.6, “Using Option Files” for more information.

Most of the steps that follow require the use of the MySQL root account or another MySQL user account that has the SUPER privilege. mysqladmin shutdown requires either the SUPER privilege or the SHUTDOWN privilege.

Step 1: Synchronize the servers.  Make the servers read-only. To do this, enable the read_only system variable by executing the following statement on both servers:

mysql> SET @@global.read_only = ON;

Then, allow the slave to catch up with the master. It is extremely important that you make sure the slave has processed all updates before continuing.

Step 2: Stop both servers.  Stop each server using mysqladmin as shown here, where username is the user name for a MySQL user having sufficient privileges to shut down the server:

shell> mysqladmin -uusername -p shutdown

Then supply this user's password at the prompt.

Step 3: Restart both servers with GTIDs enabled.  To enable GTID-based replication, each server must be started with GTID mode enabled, by setting the --gtid-mode option to ON, and with the --enforce-gtid-consistency option enabled to ensure that only statements which are safe for GTID-based replication are logged. In addition, you should start the slave with the --skip-slave-start option before configuring the slave settings. For more information on GTID related options, see Section 18.1.6.5, “Global Transaction ID Options and Variables”.

It is not mandatory to have binary logging enabled in order to use GTIDs due to the addition of the mysql.gtid_executed Table in MySQL 5.7.5. This means that you can have slave servers using GTIDs but without binary logging. Masters must always have binary logging enabled in order to be able to replicate. For example, to start a slave with GTIDs enabled but without binary logging, use at least these options:

shell> mysqld --gtid-mode=ON --enforce-gtid-consistency &

In MySQL 5.7.4 and earlier, binary logging is required to use GTIDs and both master and slave servers must be started with at least these options:

shell> mysqld --gtid-mode=ON --log-bin --enforce-gtid-consistency &

Depending on your configuration, supply additional options to mysqld.

Step 4: Direct the slave to use the master.  Tell the slave to use the master as the replication data source, and to use GTID-based auto-positioning rather than file-based positioning. Execute a CHANGE MASTER TO statement on the slave, using the MASTER_AUTO_POSITION option to tell the slave that transactions will be identified by GTIDs.

You may also need to supply appropriate values for the master's host name and port number as well as the user name and password for a replication user account which can be used by the slave to connect to the master; if these have already been set prior to Step 1 and no further changes need to be made, the corresponding options can safely be omitted from the statement shown here.

mysql> CHANGE MASTER TO
     >     MASTER_HOST = host,
     >     MASTER_PORT = port,
     >     MASTER_USER = user,
     >     MASTER_PASSWORD = password,
     >     MASTER_AUTO_POSITION = 1;

Neither the MASTER_LOG_FILE option nor the MASTER_LOG_POS option may be used with MASTER_AUTO_POSITION set equal to 1. Attempting to do so causes the CHANGE MASTER TO statement to fail with an error.

Assuming that the CHANGE MASTER TO statement has succeeded, you can then start the slave, like this:

mysql> START SLAVE;

Step 5: Disable read-only mode.  Allow the master to begin accepting updates once again by running the following statement:

mysql> SET @@global.read_only = OFF;

GTID-based replication should now be running, and you can begin (or resume) activity on the master as before. Section 18.1.3.3, “Using GTIDs for Failover and Scaleout”, discusses creation of new slaves when using GTIDs.

18.1.3.3 Using GTIDs for Failover and Scaleout

There are a number of techniques when using MySQL Replication with Global Transaction Identifiers (GTIDs) for provisioning a new slave which can then be used for scaleout, being promoted to master as necessary for failover. This section describes the following techniques:

Global transaction identifiers were added to MySQL Replication for the purpose of simplifying in general management of the replication data flow and of failover activities in particular. Each identifier uniquely identifies a set of binary log events that together make up a transaction. GTIDs play a key role in applying changes to the database: the server automatically skips any transaction having an identifier which the server recognizes as one that it has processed before. This behavior is critical for automatic replication positioning and correct failover.

The mapping between identifiers and sets of events comprising a given transaction is captured in the binary log. This poses some challenges when provisioning a new server with data from another existing server. To reproduce the identifier set on the new server, it is necessary to copy the identifiers from the old server to the new one, and to preserve the relationship between the identifiers and the actual events. This is neccessary for restoring a slave that is immediately available as a candidate to become a new master on failover or switchover.

Simple replication.  The easiest way to reproduce all identifiers and transactions on a new server is to make the new server into the slave of a master that has the entire execution history, and enable global transaction identifiers on both servers. See Section 18.1.3.2, “Setting Up Replication Using GTIDs”, for more information.

Once replication is started, the new server copies the entire binary log from the master and thus obtains all information about all GTIDs.

This method is simple and effective, but requires the slave to read the binary log from the master; it can sometimes take a comparatively long time for the new slave to catch up with the master, so this method is not suitable for fast failover or restoring from backup. This section explains how to avoid fetching all of the execution history from the master by copying binary log files to the new server.

Copying data and transactions to the slave.  Playing back the entire transaction history can be time-consuming, and represents a major bottleneck when setting up a new replication slave. To eliminate this requirement, a snapshot of the data set, the binary logs and the global transaction information the master contains is imported to the slave. The binary log is played back, after which replication can be started, allowing the slave to become current with any remaining transactions.

There are several variants of this method, the difference being in the manner in which data dumps and transactions from binary logs are transfered to the slave, as outlined here:

Data SetTransaction History
  • Use the mysql client to import a dump file created with mysqldump. Use the --master-data option to include binary logging information and --set-gtid-purged to AUTO (the default) or ON, to include information about executed transactions. You should have --gtid-mode=ON while importing the dump on the slave.

  • Stop the slave, copy the contents of the master's data directory to the slave's data directory, then restart the slave.

If gtid_mode is not ON, restart the server with GTID mode enabled.

See also Section 5.6.7.3, “Using mysqlbinlog to Back Up Binary Log Files”.

This method has the advantage that a new server is available almost immediately; only those transactions that were committed while the snapshot or dump file was being replayed still need to be obtained from the existing master. This means that the slave's availability is not instantanteous—but only a relatively short amount of time should be required for the slave to catch up with these few remaining transactions.

Copying over binary logs to the target server in advance is usually faster than reading the entire transaction execution history from the master in real time. However, it may not always be feasible to move these files to the target when required, due to size or other considerations. The two remaining methods for provisioning a new slave discussed in this section use other means to transfer information about transactions to the new slave.

Injecting empty transactions.  The master's global gtid_executed variable contains the set of all transactions executed on the master. Rather than copy the binary logs when taking a snapshot to provision a new server, you can instead note the content of gtid_executed on the server from which the snapshot was taken. Before adding the new server to the replication chain, simply commit an empty transaction on the new server for each transaction identifier contained in the master's gtid_executed, like this:

SET GTID_NEXT='aaa-bbb-ccc-ddd:N';

BEGIN;
COMMIT;

SET GTID_NEXT='AUTOMATIC';

Once all transaction identifiers have been reinstated in this way using empty transactions, you must flush and purge the slave's binary logs, as shown here, where N is the nonzero suffix of the current binary log file name:

FLUSH LOGS;
PURGE BINARY LOGS TO 'master-bin.00000N';

You should do this to prevent this server from flooding the replication stream with false transactions in the event that it is later promoted to master. (The FLUSH LOGS statement forces the creation of a new binary log file; PURGE BINARY LOGS purges the empty transactions, but retains their identifiers.)

This method creates a server that is essentially a snapshot, but in time is able to become a master as its binary log history converges with that of the replication stream (that is, as it catches up with the master or masters). This outcome is similar in effect to that obtained using the remaining provisioning method, which we discuss in the next few paragraphs.

Excluding transactions with gtid_purged.  The master's global gtid_purged variable contains the set of all transactions that have been purged from the master's binary log. As with the method discussed previously (see Injecting empty transactions), you can record the value of gtid_executed on the server from which the snapshot was taken (in place of copying the binary logs to the new server). Unlike the previous method, there is no need to commit empty transactions (or to issue PURGE BINARY LOGS); instead, you can set gtid_purged on the slave directly, based on the value of gtid_executed on the server from which the backup or snapshot was taken.

As with the method using empty transactions, this method creates a server that is functionally a snapshot, but in time is able to become a master as its binary log history converges with that of the replication master or group.

Restoring GTID mode slaves.  When restoring a slave in a GTID based replication setup that has encountered an error, injecting an empty transaction may not solve the problem because an event does not have a GTID.

Use mysqlbinlog to find the next transaction, which is probably the first transaction in the next log file after the event. Copy everything up to the COMMIT for that transaction, being sure to include the SET @@SESSION.GTID_NEXT. Even if you are not using row-based replication, you can still run binary log row events in the command line client.

Stop the slave and run the transaction you copied. The mysqlbinlog output sets the delimiter to /*!*/;, so set it back:

mysql> DELIMITER ;
		

Restart replication from the correct position automatically:

mysql> SET GTID_NEXT=automatic;
mysql> RESET SLAVE;
mysql> START SLAVE;

18.1.3.4 Restrictions on Replication with GTIDs

Because GTID-based replication is dependent on transactions, some features otherwise available in MySQL are not supported when using it. This section provides information about restrictions on and limitations of replication with GTIDs.

Updates involving nontransactional storage engines.  When using GTIDs, updates to tables using nontransactional storage engines such as MyISAM cannot be made in the same statement or transaction as updates to tables using transactional storage engines such as InnoDB.

This restriction is due to the fact that updates to tables that use a nontransactional storage engine mixed with updates to tables that use a transactional storage engine within the same transaction can result in multiple GTIDs being assigned to the same transaction.

Such problems can also occur when the master and the slave use different storage engines for their respective versions of the same table, where one storage engine is transactional and the other is not.

In any of the cases just mentioned, the one-to-one correspondence between transactions and GTIDs is broken, with the result that GTID-based replication cannot function correctly.

CREATE TABLE ... SELECT statements.  CREATE TABLE ... SELECT is not safe for statement-based replication. When using row-based replication, this statement is actually logged as two separate events—one for the creation of the table, and another for the insertion of rows from the source table into the new table just created. When this statement is executed within a transaction, it is possible in some cases for these two events to receive the same transaction identifier, which means that the transaction containing the inserts is skipped by the slave. Therefore, CREATE TABLE ... SELECT is not supported when using GTID-based replication.

Temporary tables.  CREATE TEMPORARY TABLE and DROP TEMPORARY TABLE statements are not supported inside transactions when using GTIDs (that is, when the server was started with the --enforce-gtid-consistency option). It is possible to use these statements with GTIDs enabled, but only outside of any transaction, and only with autocommit=1.

Preventing execution of unsupported statements.  To prevent execution of statements that would cause GTID-based replication to fail, all servers must be started with the --enforce-gtid-consistency option when enabling GTIDs. This causes statements of any of the types discussed previously in this section to fail with an error.

For information about other required startup options when enabling GTIDs, see Section 18.1.3.2, “Setting Up Replication Using GTIDs”.

sql_slave_skip_counter is not supported when using GTIDs. If you need to skip transactions, use the value of the master's gtid_executed variable instead; see Injecting empty transactions, for more information.

GTID mode and mysqldump.  It is possible to import a dump made using mysqldump into a MySQL Server running with GTID mode enabled, provided that there are no GTIDs in the target server's binary log.

GTID mode and mysql_upgrade.  It is not recommended to use mysql_upgrade with the --write-binlog option on a MySQL Server running with --gtid-mode=ON because mysql_upgrade can make changes to system tables that use the MyISAM storage engine, which is non-transactional.

18.1.4 MySQL Multi-Source Replication

This section describes MySQL Multi-Source Replication, included in MySQL 5.7.6 and later. Multi-source replication enables you to replicate from multiple immediate masters in parallel. This section describes multi-source replication, and how to configure, monitor and troubleshoot it.

18.1.4.1 MySQL Multi-Source Replication Overview

MySQL Multi-Source Replication enables a replication slave to receive transactions from multiple sources simultaneously. Multi-source replication can be used to back up multiple servers to a single server, to merge table shards, and consolidate data from multiple servers to a single server. Multi-source replication does not implement any conflict detection or resolution when applying the transactions, and those tasks are left to the application if required. In a multi-source replication topology, a slave creates a replication channel for each master that it should receive transactions from. See Section 18.2.3, “Replication Channels”. The following sections describe how to set up multi-source replication.

18.1.4.2 Multi-Source Replication Tutorials

This section provides tutorials on how to configure masters and slaves for multi-source replication, and how to start, stop and reset multi-source slaves.

18.1.4.2.1 Configuring Multi-Source Replication

This section explains how to configure a multi-source replication topology, and provides details about configuring masters and slaves. Such a topology requires at least two masters and one slave configured.

Masters in a multi-source replication topology can be configured to use either global transaction identifier (GTID) based replication, or binary log position-based replication. See Section 18.1.3.2, “Setting Up Replication Using GTIDs” for how to configure a master using GTID based replication. See Section 18.1.2.1, “Setting the Replication Master Configuration” for how to configure a master using file position based replication.

Slaves in a multi-source replication topology require TABLE based repositories. Multi-source replication is not compatible with FILE based repositories. The type of repository being used by mysqld can be configured either at startup, or dynamically.

To configure the type of repository used by a replication slave at startup, start mysqld with the following options:

--master-info-repository=TABLE --relay-log-info-repository=TABLE

To modify an existing replication slave that is using a FILE repository to use TABLE repositories, convert the existing replication repositories dynamically by running the following commands:

STOP SLAVE;
SET GLOBAL master_info_repository = 'TABLE';
SET GLOBAL relay_log_info_repository = 'TABLE';
18.1.4.2.2 Adding a GTID Based Master to a Multi-Source Replication Slave

This section assumes you have enabled GTID based transactions on the master using gtid_mode=ON, enabled a replication user, and ensured that the slave is using TABLE based replication repositories. Use the CHANGE MASTER TO statement to add a new master to a channel by using a FOR CHANNEL channel clause. For more information on replication channels, see Section 18.2.3, “Replication Channels”

For example, to add a new master with the host name master1 using port 3451 to a channel called master-1:


CHANGE MASTER TO MASTER_HOST='master1', MASTER_USER='rpl', MASTER_PORT=3451, MASTER_PASSWORD='', \
MASTER_AUTO_POSITION = 1 FOR CHANNEL 'master-1';

Multi-source replication is compatible with auto-positioning. See Section 14.4.2.1, “CHANGE MASTER TO Syntax” for more information.

Repeat this process for each extra master that you want to add to a channel, changing the host name, port and channel as appropriate.

18.1.4.2.3 Adding a Binary Log Based Master to a Multi-Source Replication Slave

This section assumes you have enabled binary logging on the master using --log-bin, enabled a replication user, noted the current binary log position, and ensured that the slave is using TABLE based replication repositories. You need to know the current MASTER_LOG_FILE and MASTER_LOG_POSITION. Use the CHANGE MASTER TO statement to add a new master to a channel by specifying a FOR CHANNEL channel clause. For example, to add a new master with the host name master1 using port 3451 to a channel called master-1:


CHANGE MASTER TO MASTER_HOST='master1', MASTER_USER='rpl', MASTER_PORT=3451, MASTER_PASSWORD='' \
MASTER_LOG_FILE='master1-bin.000006', MASTER_LOG_POS=628 FOR CHANNEL 'master-1';

Repeat this process for each extra master that you want to add to a channel, changing the host name, port and channel as appropriate.

18.1.4.2.4 Starting Multi-Source Replication Slaves

Once you have added all of the channels you want to use as replication masters, use a START SLAVE thread_types statement to start replication. When you have enabled multiple channels on a slave, you can choose to either start all channels, or select a specific channel to start.

  • To start all currently configured replication channels:

     
    START SLAVE thread_types;
  • To start only a named channel, use a FOR CHANNEL channel clause:

     
    START SLAVE thread_types FOR CHANNEL channel;
    

Use the thread_types option to choose specific threads you want the above statements to start on the slave. See Section 14.4.2.6, “START SLAVE Syntax” for more information.

18.1.4.2.5 Stopping Multi-Source Replication Slaves

The STOP SLAVE statement can be used to stop a multi-source replication slave. By default, if you use the STOP SLAVE statement on a multi-source replication slave all channels are stopped. Optionally, use the FOR CHANNEL channel clause to stop only a specific channel.

  • To stop all currently configured replication channels:

    
    STOP SLAVE thread_types;
  • To stop only a named channel, use a FOR CHANNEL channel clause:

     
    STOP SLAVE thread_types FOR CHANNEL channel;
    

Use the thread_types option to choose specific threads you want the above statements to stop on the slave. See Section 14.4.2.7, “STOP SLAVE Syntax” for more information.

18.1.4.2.6 Resetting Multi-Source Replication Slaves

The RESET SLAVE statement can be used to reset a multi-source replication slave. By default, if you use the RESET SLAVE statement on a multi-source replication slave all channels are reset. Optionally, use the FOR CHANNEL channel clause to reset only a specific channel.

  • To reset all currently configured replication channels:

     
    RESET SLAVE;
  • To reset only a named channel, use a FOR CHANNEL channel clause:

     
    RESET SLAVE FOR CHANNEL channel;
    

See Section 14.4.2.4, “RESET SLAVE Syntax” for more information.

18.1.4.3 Multi-Source Replication Monitoring

To monitor the status of replication channels the following options exist:

  • Using the replication Performance Schema tables. The first column of these tables is Channel_Name. This enables you to write complex queries based on Channel_Name as a key. See Section 24.10.11, “Performance Schema Replication Tables”.

  • Using SHOW SLAVE STATUS FOR CHANNEL channel_name. By default, if the FOR CHANNEL channel_name clause is not used, this statement shows the slave status for all channels with one row per channel. The identifier channel_name is added as a column in the result set. If a FOR CHANNEL channel_name clause is provided, the results show the status of only the named replication channel.

Note

The SHOW VARIABLES statement does not work with multiple replication channels. The information that was available through these variables has been migrated to the replication performance tables. Using a SHOW VARIABLES statement in a topology with multiple channels shows the status of only the default channel.

18.1.4.3.1 Monitoring Channels Using Performance Schema Tables

This section explains how to use the replication Performance Schema tables to monitor channels. You can choose to monitor all channels, or a subset of the existing channels.

To monitor the connection status of all channels:

mysql> SELECT * FROM replication_connection_status\G;
*************************** 1. row ***************************
CHANNEL_NAME: master1
GROUP_NAME:
SOURCE_UUID: 046e41f8-a223-11e4-a975-0811960cc264
THREAD_ID: 24
SERVICE_STATE: ON
COUNT_RECEIVED_HEARTBEATS: 0
LAST_HEARTBEAT_TIMESTAMP: 0000-00-00 00:00:00
RECEIVED_TRANSACTION_SET: 046e41f8-a223-11e4-a975-0811960cc264:4-37
LAST_ERROR_NUMBER: 0
LAST_ERROR_MESSAGE:
LAST_ERROR_TIMESTAMP: 0000-00-00 00:00:00
*************************** 2. row ***************************
CHANNEL_NAME: master2
GROUP_NAME:
SOURCE_UUID: 7475e474-a223-11e4-a978-0811960cc264
THREAD_ID: 26
SERVICE_STATE: ON
COUNT_RECEIVED_HEARTBEATS: 0
LAST_HEARTBEAT_TIMESTAMP: 0000-00-00 00:00:00
RECEIVED_TRANSACTION_SET: 7475e474-a223-11e4-a978-0811960cc264:4-6
LAST_ERROR_NUMBER: 0
LAST_ERROR_MESSAGE:
LAST_ERROR_TIMESTAMP: 0000-00-00 00:00:00
2 rows in set (0.00 sec)
	    

In the above output there are two channels enabled, and as shown by the CHANNEL_NAME field they are called master1 and master2.

The addition of the CHANNEL_NAME field enables you to query the Performance Schema tables for a specific channel. To monitor the connection status of a named channel, use a WHERE channel_name=channel clause:

mysql> SELECT * FROM replication_connection_status WHERE channel_name='master1'\G
*************************** 1. row ***************************
CHANNEL_NAME: master1
GROUP_NAME:
SOURCE_UUID: 046e41f8-a223-11e4-a975-0811960cc264
THREAD_ID: 24
SERVICE_STATE: ON
COUNT_RECEIVED_HEARTBEATS: 0
LAST_HEARTBEAT_TIMESTAMP: 0000-00-00 00:00:00
RECEIVED_TRANSACTION_SET: 046e41f8-a223-11e4-a975-0811960cc264:4-37
LAST_ERROR_NUMBER: 0
LAST_ERROR_MESSAGE:
LAST_ERROR_TIMESTAMP: 0000-00-00 00:00:00
1 row in set (0.00 sec)

Similarly, the WHERE channel_name=channel clause can be used to monitor the other replication Performance Schema tables for a specific channel. For more information, see Section 24.10.11, “Performance Schema Replication Tables”.

18.1.4.4 Multi-Source Replication Error Messages

New error codes and messages have been added to MySQL 5.7.6 to provide information about errors encountered in a multi-source replication topology. These error codes and messages are only emitted when multi-source replication is enabled, and provide information related to the channel which generated the error. For example:

Slave is already running and Slave is already stopped have been replaced with Replication thread(s) for channel channel_name are already running and Replication threads(s) for channel channel_name are already stopped respectively.

The server log messages have also been changed to indicate which channel the log messages relate to. This makes debugging and tracing easier.

18.1.5 Changing Replication Modes on Online Servers

This section describes how to change the mode of replication being used without having to take the server offline. This is new functionality added in MySQL 5.7.6.

18.1.5.1 Replication Mode Concepts

To be able to safely configure the replication mode of an online server it is important to understand some key concepts of replication. This section explains these concepts and is essential reading before attempting to modify the replication mode of an online server.

The modes of replication available in MySQL rely on different techniques for identifying transactions which are logged. The types of transactions used by replication are as follows:

  • GTID transactions are identified by a global transaction identifier (GTID) in the form UUID:NUMBER. Every GTID transaction in a log is always preceded by a Gtid_log_event. GTID transactions can be addressed using either the GTID or using the file name and position.

  • Anonymous transactions do not have a GTID assigned, and MySQL 5.7.6 and later ensures that every anonymous transaction in a log is preceded by an Anonymous_gtid_log_event. In previous versions, anonymous transactions were not preceded by any particular event. Anonymous transactions can only be addressed using file name and position.

When using GTIDs you can take advantage of auto-positioning and automatic fail-over, as well as use WAIT_FOR_EXECUTED_GTID_SET(), session_track_gtids, and monitor replicated transactions using Performance Schema tables. With GTIDs enabled you cannot use sql_slave_skip_counter, instead use empty transactions.

The changes introduced by MySQL 5.7.6 mean that transactions in a relay log that was received from a master running a previous version of MySQL may not be preceded by any particular event at all, but after being replayed and logged in the slave's binary log, they are preceded with an Anonymous_gtid_log_event.

The ability to configure the replication mode online means that the gtid_mode and enforce_gtid_consistency variables are now both dynamic and can be set by SUPER from a top-level statement. In previous versions, both of these variables could only be configured using the appropriate option at server start, meaning that changes to the replication mode required a server restart. In all versions gtid_mode could be set to ON or OFF, which corresponded to whether GTIDs were used to identify transactions or not. When gtid_mode=ON it is not possible to replicate anonymous transactions, and when gtid_mode=OFF only anonymous transactions can be replicated. As of MySQL 5.7.6, the gtid_mode variable has two additional states, OFF_PERMISSIVE and ON_PERMISSIVE. When gtid_mode=OFF_PERMISSIVE then new transactions are anonymous while permitting replicated transactions to be either GTID or anonymous transactions. When gtid_mode=ON_PERMISSIVE then new transactions use GTIDs while permitting replicated transactions to be either GTID or anonymous transactions. This means it is possible to have a replication topology that has servers using both anonymous and GTID transactions. For example a master with gtid_mode=ON could be replicating to a slave with gtid_mode=ON_PERMISSIVE. The valid values for gtid_mode are as follows and in this order:

  • OFF

  • OFF_PERMISSIVE

  • ON_PERMISSIVE

  • ON

It is important to note that the state of gtid_mode can only be changed by one step at a time based on the above order. For example, if gtid_mode is currently set to OFF_PERMISSIVE, it is possible to change to OFF or ON_PERMISSIVE but not to ON. This is to ensure that the process of changing from anonymous transactions to GTID transactions online is correctly handled by the server. When you switch between gtid_mode=ON and gtid_mode=OFF, the GTID state (in other words the value of gtid_executed) is persistent. This ensures that the GTID set that has been applied by the server is always retained, regardless of changes between types of gtid_mode.

As part of the changes introduced by MySQL 5.7.6, the fields related to GTIDs have been modified so that they display the correct information regardless of the currently selected gtid_mode. This means that fields which display GTID sets, such as gtid_executed, gtid_purged, RECEIVED_TRANSACTION_SET in the replication_connection_status Performance Schema table, and the GTID related results of SHOW SLAVE STATUS, now return the empty string when there are no GTIDs present. Fields that display a single GTID, such as CURRENT_TRANSACTION in the replication_applier_status_by_worker Performance Schema table, now display ANONYMOUS when GTID transactions are not being used.

Replication from a master using gtid_mode=ON provides the ability to use auto-positioning, configured using the CHANGE MASTER TO MASTER_AUTO_POSITION = 1; statement. The replication topology being used impacts on whether it is possible to enable auto-positioning or not, as this feature relies on GTIDs and is not compatible with anonymous transactions. An error is generated if auto-positioning is enabled and an anonymous transaction is encountered. It is strongly recommended to ensure there are no anonymous transactions remaining in the topology before enabling auto-positioning, see Section 18.1.5.2, “Enabling GTID Transactions Online”. The valid combinations of gtid_mode and auto-positioning on master and slave are shown in the following table, where the master's gtid_mode is shown on the horizontal and the slave's gtid_mode is on the vertical:

Table 18.1 Valid Combinations of Master and Slave gtid_mode

Master/Slave gtid_mode

OFF
OFF_PERMISSIVE
ON_PERMISSIVE
ON
OFF

Y

Y

N

N

OFF_PERMISSIVE

Y

Y

Y

Y*

ON_PERMISSIVE

Y

Y

Y

Y*

ON

N

N

Y

Y*


In the above table, the entries are:

  • Y: the gtid_mode of master and slave is compatible

  • N: the gtid_mode of master and slave is not compatible

  • *: auto-positioning can be used

The currently selected gtid_mode also impacts on the gtid_next variable. The following table shows the behavior of the server for the different values of gtid_mode and gtid_next.

Table 18.2 Valid Combinations of gtid_mode and gtid_next

gtid_next

AUTOMATIC

binary log on

AUTOMATIC

binary log off

ANONYMOUS

UUID:NUMBER

OFF

ANONYMOUS

ANONYMOUS

ANONYMOUS

Error

OFF_PERMISSIVE

ANONYMOUS

ANONYMOUS

ANONYMOUS

UUID:NUMBER

ON_PERMISSIVE

New GTID

ANONYMOUS

ANONYMOUS

UUID:NUMBER

ON

New GTID

ANONYMOUS

Error

UUID:NUMBER


In the above table, the entries are:

  • ANONYMOUS: generate an anonymous transaction.

  • Error: generate an error and fail to execute SET GTID_NEXT.

  • UUID:NUMBER: generate a GTID with the specified UUID:NUMBER.

  • New GTID: generate a GTID with an automatically generated number.

When the binary log is off and gtid_next is set to AUTOMATIC, then no GTID is generated. This is consistent with the behavior of previous versions.

18.1.5.2 Enabling GTID Transactions Online

This section describes how to enable GTID transactions, and optionally auto-positioning, on servers that are already online and using anonymous transactions. This procedure does not require taking the server offline and is suited to use in production. However, if you have the possibility to take the servers offline when enabling GTID transactions that process is easier.

Before you start, ensure that the servers meet the following pre-conditions:

  • All servers in your topology must use MySQL 5.7.6 or later. You cannot enable GTID transactions online on any single server unless all servers which are in the topology are using this version.

  • All servers have gtid_mode set to the default value OFF.

The following procedure can be paused at any time and later resumed where it was, or reversed by jumping to the corresponding step of Section 18.1.5.3, “Disabling GTID Transactions Online”, the online procedure to disable GTIDs. This makes the procedure fault-tolerant because any unrelated issues that may appear in the middle of the procedure can be handled as usual, and then the procedure continued where it was left off.

Note

It is crucial that you complete every step before continuing to the next step.

To enable GTID transactions:

  1. On each server, execute:

    SET @@GLOBAL.ENFORCE_GTID_CONSISTENCY = WARN;

    Let the server run for a while with your normal workload and monitor the logs. If this step causes any warnings in the log, adjust your application so that it only uses GTID-compatible features and does not generate any warnings.

    Important

    This is the first important step. You must ensure that no warnings are being generated in the error logs before going to the next step.

  2. On each server, execute:

    SET @@GLOBAL.ENFORCE_GTID_CONSISTENCY = ON;
  3. On each server, execute:

    SET @@GLOBAL.GTID_MODE = OFF_PERMISSIVE;

    It does not matter which server executes this statement first, but it is important that all servers complete this step before any server begins the next step.

  4. On each server, execute:

    SET @@GLOBAL.GTID_MODE = ON_PERMISSIVE;

    It does not matter which server executes this statement first.

  5. On each server, wait until the status variable ONGOING_ANONYMOUS_TRANSACTION_COUNT is zero. This can be checked using:

    SHOW STATUS LIKE 'ONGOING_ANONYMOUS_TRANSACTION_COUNT';
    Note

    On a replication slave, it is theoretically possible that this shows zero and then non-zero again. This is not a problem, it suffices that it shows zero once.

  6. Wait for all transactions generated up to step 5 to replicate to all servers. You can do this without stopping updates: the only important thing is that all anonymous transactions get replicated.

    See Section 18.1.5.4, “Verifying Replication of Anonymous Transactions” for one method of checking that all anonymous transactions have replicated to all servers.

  7. If you use binary logs for anything other than replication, for example point in time backup and restore, wait until you do not need the old binary logs having transactions without GTIDs.

    For instance, after step 6 has completed, you can execute FLUSH LOGS on the server where you are taking backups. Then either explicitly take a backup or wait for the next iteration of any periodic backup routine you may have set up.

    Ideally, wait for the server to purge all binary logs that existed when step 6 was completed. Also wait for any backup taken before step 6 to expire.

    Important

    This is the second important point. It is vital to understand that binary logs containing anonymous transactions, without GTIDs cannot be used after the next step. After this step, you must be sure that transactions without GTIDs do not exist anywhere in the topology.

  8. On each server, execute:

    SET @@GLOBAL.GTID_MODE = ON;
  9. On each server, add gtid-mode=ON to my.cnf.

    You are now guaranteed that all transactions have a GTID (except transactions generated in step 5 or earlier, which have already been processed). To start using the GTID protocol so that you can later perform automatic fail-over, execute the following on each slave. Optionally, if you use multi-source replication, do this for each channel and include the FOR CHANNEL channel clause:

    
    STOP SLAVE [FOR CHANNEL 'channel'];
    CHANGE MASTER TO MASTER_AUTO_POSITION = 1 [FOR CHANNEL 'channel'];
    START SLAVE [FOR CHANNEL 'channel'];

18.1.5.3 Disabling GTID Transactions Online

This section describes how to disable GTID transactions on servers that are already online. This procedure does not require taking the server offline and is suited to use in production. However, if you have the possibility to take the servers offline when disabling GTIDs mode that process is easier.

The process is similar to enabling GTID transactions while the server is online, but reversing the steps. The only thing that differs is the point at which you wait for logged transactions to replicate.

Before you start, ensure that the servers meet the following pre-conditions:

  • All servers in your topology must use MySQL 5.7.6 or later. You cannot disable GTID transactions online on any single server unless all servers which are in the topology are using this version.

  • All servers have gtid_mode set to ON.

  1. Execute the following on each slave, and if you using multi-source replication, do it for each channel and include the FOR CHANNEL channel clause:

    
    STOP SLAVE [FOR CHANNEL 'channel'];
    CHANGE MASTER TO MASTER_AUTO_POSITION = 0, MASTER_LOG_FILE = file, \
    MASTER_LOG_POS = position [FOR CHANNEL 'channel'];
    START SLAVE [FOR CHANNEL 'channel'];
     
     
  2. On each server, execute:

    SET @@GLOBAL.GTID_MODE = ON_PERMISSIVE;
  3. On each server, execute:

    SET @@GLOBAL.GTID_MODE = OFF_PERMISSIVE;
  4. On each server, wait until the variable @@GLOBAL.GTID_OWNED is equal to the empty string. This can be checked using:

    SELECT @@GLOBAL.GTID_OWNED;

    On a replication slave, it is theoretically possible that this is empty and then nonempty again. This is not a problem, it suffices that it is empty once.

  5. Wait for all transactions that currently exist in any binary log to replicate to all slaves. See Section 18.1.5.4, “Verifying Replication of Anonymous Transactions” for one method of checking that all anonymous transactions have replicated to all servers.

  6. If you use binary logs for anything else than replication, for example to do point in time backup or restore: wait until you do not need the old binary logs having GTID transactions.

    For instance, after step 5 has completed, you can execute FLUSH LOGS on the server where you are taking the backup. Then either explicitly take a backup or wait for the next iteration of any periodic backup routine you may have set up.

    Ideally, wait for the server to purge all binary logs that existed when step 5 was completed. Also wait for any backup taken before step 5 to expire.

    Important

    This is the one important point during this procedure. It is important to understand that logs containing GTID transactions cannot be used after the next step. Before proceeding you must be sure that GTID transactions do not exist anywhere in the topology.

  7. On each server, execute:

    SET @@GLOBAL.GTID_MODE = OFF;
  8. On each server, set gtid-mode=OFF in my.cnf.

    If you want to set enforce_gtid_consistency=OFF, you can do so now. After setting it, you should add enforce_gtid_consistency=OFF to your configuration file.

If you want to downgrade to an earlier version of MySQL, you can do so now, using the normal downgrade procedure.

18.1.5.4 Verifying Replication of Anonymous Transactions

This section explains how to monitor a replication topology and verify that all anonymous transactions have been replicated. This is helpful when changing the replication mode online as you can verify that it is safe to change to GTID transactions.

There are several possible ways to wait for transactions to replicate:

The simplest method, which works regardless of your topology but relies on timing is as follows: if you are sure that the slave never lags more than N seconds, just wait for a bit more than N seconds. Or wait for a day, or whatever time period you consider safe for your deployment.

A safer method in the sense that it does not depend on timing: if you only have a master with one or more slaves, do the following:

  1. On the master, execute:

    SHOW MASTER STATUS;

    Note down the values in the File and Position column.

  2. On every slave, use the file and position information from the master to execute:

    SELECT MASTER_POS_WAIT(file, position);

If you have a master and multiple levels of slaves, or in other words you have slaves of slaves, repeat step 2 on each level, starting from the master, then all the direct slaves, then all the slaves of slaves, and so on.

If you use a circular replication topology where multiple servers may have write clients, perform step 2 for each master-slave connection, until you have completed the full circle. Repeat the whole process so that you do the full circle twice.

For example, suppose you have three servers A, B, and C, replicating in a circle so that A -> B -> C -> A. The procedure is then:

  • Do step 1 on A and step 2 on B.

  • Do step 1 on B and step 2 on C.

  • Do step 1 on C and step 2 on A.

  • Do step 1 on A and step 2 on B.

  • Do step 1 on B and step 2 on C.

  • Do step 1 on C and step 2 on A.

18.1.6 Replication and Binary Logging Options and Variables

The following sections contain information about mysqld options and server variables that are used in replication and for controlling the binary log. Options and variables for use on replication masters and replication slaves are covered separately, as are options and variables relating to binary logging and global transaction identifiers (GTIDs). A set of quick-reference tables providing basic information about these options and variables is also included.

Of particular importance is the --server-id option.

Command-Line Format--server-id=#
System VariableNameserver_id
Variable ScopeGlobal
Dynamic VariableYes
Permitted ValuesTypeinteger
Default0
Min Value0
Max Value4294967295

This option is common to both master and slave replication servers, and is used in replication to enable master and slave servers to identify themselves uniquely. For additional information, see Section 18.1.6.2, “Replication Master Options and Variables”, and Section 18.1.6.3, “Replication Slave Options and Variables”.

On the master and each slave, you must use the --server-id option to establish a unique replication ID in the range from 1 to 232 − 1. Unique, means that each ID must be different from every other ID in use by any other replication master or slave. For example, server-id=3.

In MySQL 5.7.2 and earlier, if you start a master server without using --server-id to set its ID, the default ID is 0. In this case, the master refuses connections from all slaves, slaves refuse to connect to the master, and the server sets the server_id system variable to 1. In MySQL 5.7.3 and later, the --server-id must be used if binary logging is enabled, and a value of 0 is not changed by the server. If you specify --server-id without an argument, the effect is the same as using 0. In either case, if the server_id is 0, binary logging takes place, but slaves cannot connect to the master, nor can any other servers connect to it as slaves. (Bug #11763963, Bug #56718)

For more information, see Section 18.1.2.5.1, “Setting the Replication Slave Configuration”.

server_uuid

In MySQL 5.7, the server generates a true UUID in addition to the --server-id supplied by the user. This is available as the global, read-only variable server_uuid.

Note

The presence of the server_uuid system variable in MySQL 5.7 does not change the requirement for setting a unique --server-id for each MySQL server as part of preparing and running MySQL replication, as described earlier in this section.

System VariableNameserver_uuid
Variable ScopeGlobal
Dynamic VariableNo
Permitted ValuesTypestring

When starting, the MySQL server automatically obtains a UUID as follows:

  1. Attempt to read and use the UUID written in the file data_dir/auto.cnf (where data_dir is the server's data directory).

  2. If data_dir/auto.cnf is not found, generate a new UUID and save it to this file, creating the file if necessary.

The auto.cnf file has a format similar to that used for my.cnf or my.ini files. In MySQL 5.7, auto.cnf has only a single [auto] section containing a single server_uuid setting and value; the file's contents appear similar to what is shown here:

[auto]
server_uuid=8a94f357-aab4-11df-86ab-c80aa9429562
Important

The auto.cnf file is automatically generated; do not attempt to write or modify this file.

When using MySQL replication, masters and slaves know each other's UUIDs. The value of a slave's UUID can be seen in the output of SHOW SLAVE HOSTS. Once START SLAVE has been executed, the value of the master's UUID is available on the slave in the output of SHOW SLAVE STATUS.

Note

Issuing a STOP SLAVE or RESET SLAVE statement does not reset the master's UUID as used on the slave.

A server's server_uuid is also used in GTIDs for transactions originating on that server. For more information, see Section 18.1.3, “Replication with Global Transaction Identifiers”.

When starting, the slave I/O thread generates an error and aborts if its master's UUID is equal to its own unless the --replicate-same-server-id option has been set. In addition, the slave I/O thread generates a warning if either of the following is true:

18.1.6.1 Replication and Binary Logging Option and Variable Reference

The following tables list basic information about the MySQL command-line options and system variables applicable to replication and the binary log.

Table 18.3 Summary of Replication options and variables in MySQL 5.7

Option or Variable Name
Command Line System Variable Status Variable
Option File Scope Dynamic
Notes

abort-slave-event-count

Yes No No
Yes No

DESCRIPTION: Option used by mysql-test for debugging and testing of replication

binlog_gtid_simple_recovery

Yes Yes No
Yes Global No

DESCRIPTION: Controls how binary logs are iterated during GTID recovery

Com_change_master

No No Yes
No Both No

DESCRIPTION: Count of CHANGE MASTER TO statements

Com_show_master_status

No No Yes
No Both No

DESCRIPTION: Count of SHOW MASTER STATUS statements

Com_show_new_master

No No Yes
No Both No

DESCRIPTION: Count of SHOW NEW MASTER statements

Com_show_slave_hosts

No No Yes
No Both No

DESCRIPTION: Count of SHOW SLAVE HOSTS statements

Com_show_slave_status

No No Yes
No Both No

DESCRIPTION: Count of SHOW SLAVE STATUS statements

Com_show_slave_status_nonblocking

No No Yes
No Both No

DESCRIPTION: Count of SHOW SLAVE STATUS NONBLOCKING statements

Com_slave_start

No No Yes
No Both No

DESCRIPTION: Count of START SLAVE statements

Com_slave_stop

No No Yes
No Both No

DESCRIPTION: Count of STOP SLAVE statements

disconnect-slave-event-count

Yes No No
Yes No

DESCRIPTION: Option used by mysql-test for debugging and testing of replication

enforce-gtid-consistency

Yes Yes No
Yes Global Yes

DESCRIPTION: Prevents execution of statements that cannot be logged in a transactionally safe manner

enforce_gtid_consistency

Yes Yes No
Yes Global Yes

DESCRIPTION: Prevents execution of statements that cannot be logged in a transactionally safe manner

executed-gtids-compression-period

Yes No No
Yes No

DESCRIPTION: Deprecated and will be removed in a future version. Use the renamed gtid-executed-compression-period instead.

executed_gtids_compression_period

No Yes No
No Global Yes

DESCRIPTION: Deprecated and will be removed in a future version. Use the renamed gtid_executed_compression_period instead.

gtid-executed-compression-period

Yes No No
Yes No

DESCRIPTION: Compress gtid_executed table each time this many transactions have occurred. 0 means never compress this table. Applies only when binary logging is disabled.

gtid-mode

Yes Yes No
Yes Global Yes

DESCRIPTION: Controls whether GTID based logging is enabled and what type of transactions the logs can contain

gtid_executed

No Yes No
No Global No

DESCRIPTION: Global: All GTIDs in the binary log (global) or current transaction (session). Read-only.

gtid_executed_compression_period

No Yes No
No Global Yes

DESCRIPTION: Compress gtid_executed table each time this many transactions have occurred. 0 means never compress this table. Applies only when binary logging is disabled.

gtid_mode

No Yes No
No Global Yes

DESCRIPTION: Controls whether GTID based logging is enabled and what type of transactions the logs can contain

gtid_next

No Yes No
No Session Yes

DESCRIPTION: Specifies the GTID for the next statement to execute. See documentation for details.

gtid_owned

No Yes No
No Both No

DESCRIPTION: The set of GTIDs owned by this client (session), or by all clients, together with the thread ID of the owner (global). Read-only.

gtid_purged

No Yes No
No Global Yes

DESCRIPTION: The set of all GTIDs that have been purged from the binary log.

init_slave

Yes Yes No
Yes Global Yes

DESCRIPTION: Statements that are executed when a slave connects to a master

log-slave-updates

Yes Yes No
Yes Global No

DESCRIPTION: Tells the slave to log the updates performed by its SQL thread to its own binary log

log_slave_updates

Yes Yes No
Yes Global No

DESCRIPTION: Whether the slave should log the updates performed by its SQL thread to its own binary log. Read-only; set using the --log-slave-updates server option.

log_statements_unsafe_for_binlog

No Yes No
No Global Yes

DESCRIPTION: Disables error 1592 warnings being written to the error log

master-info-file

Yes No No
Yes No

DESCRIPTION: The location and name of the file that remembers the master and where the I/O replication thread is in the master's binary logs

master-info-repository

Yes No No
Yes No

DESCRIPTION: Whether to write master status information and replication I/O thread location in the master's binary logs to a file or table.

master-retry-count

Yes No No
Yes No

DESCRIPTION: Number of tries the slave makes to connect to the master before giving up

master_info_repository

Yes Yes No
Yes Global Yes

DESCRIPTION: Whether to write master status information and replication I/O thread location in the master's binary logs to a file or table

relay-log

Yes Yes No
Yes Global No

DESCRIPTION: The location and base name to use for relay logs

relay-log-index

Yes Yes No
Yes Global No

DESCRIPTION: The location and name to use for the file that keeps a list of the last relay logs

relay-log-info-file

Yes No No
Yes No

DESCRIPTION: The location and name of the file that remembers where the SQL replication thread is in the relay logs

relay-log-info-repository

Yes No No
Yes No

DESCRIPTION: Whether to write the replication SQL thread's location in the relay logs to a file or a table.

relay-log-recovery

Yes No No
Yes No

DESCRIPTION: Enables automatic recovery of relay log files from master at startup

relay_log_basename

No Yes No
No Global No

DESCRIPTION: Complete path to relay log, including filename

relay_log_index

Yes Yes No
Yes Global No

DESCRIPTION: The name of the relay log index file

relay_log_info_file

Yes Yes No
Yes Global No

DESCRIPTION: The name of the file in which the slave records information about the relay logs

relay_log_info_repository

No Yes No
No Global Yes

DESCRIPTION: Whether to write the replication SQL thread's location in the relay logs to a file or a table

relay_log_purge

Yes Yes No
Yes Global Yes

DESCRIPTION: Determines whether relay logs are purged

relay_log_recovery

Yes Yes No
Yes Global Yes

DESCRIPTION: Whether automatic recovery of relay log files from master at startup is enabled; must be enabled for a crash-safe slave.

relay_log_space_limit

Yes Yes No
Yes Global No

DESCRIPTION: Maximum space to use for all relay logs

replicate-do-db

Yes No No
Yes No

DESCRIPTION: Tells the slave SQL thread to restrict replication to the specified database

replicate-do-table

Yes No No
Yes No

DESCRIPTION: Tells the slave SQL thread to restrict replication to the specified table

replicate-ignore-db

Yes No No
Yes No

DESCRIPTION: Tells the slave SQL thread not to replicate to the specified database

replicate-ignore-table

Yes No No
Yes No

DESCRIPTION: Tells the slave SQL thread not to replicate to the specified table

replicate-rewrite-db

Yes No No
Yes No

DESCRIPTION: Updates to a database with a different name than the original

replicate-same-server-id

Yes No No
Yes No

DESCRIPTION: In replication, if set to 1, do not skip events having our server id

replicate-wild-do-table

Yes No No
Yes No

DESCRIPTION: Tells the slave thread to restrict replication to the tables that match the specified wildcard pattern

replicate-wild-ignore-table

Yes No No
Yes No

DESCRIPTION: Tells the slave thread not to replicate to the tables that match the given wildcard pattern

report-host

Yes Yes No
Yes Global No

DESCRIPTION: Host name or IP of the slave to be reported to the master during slave registration

report-password

Yes Yes No
Yes Global No

DESCRIPTION: An arbitrary password that the slave server should report to the master. Not the same as the password for the MySQL replication user account.

report-port

Yes Yes No
Yes Global No

DESCRIPTION: Port for connecting to slave reported to the master during slave registration

report-user

Yes Yes No
Yes Global No

DESCRIPTION: An arbitrary user name that a slave server should report to the master. Not the same as the name used with the MySQL replication user account.

Rpl_semi_sync_master_clients

No No Yes
No Global No

DESCRIPTION: Number of semisynchronous slaves

rpl_semi_sync_master_enabled

No Yes No
No Global Yes

DESCRIPTION: Whether semisynchronous replication is enabled on the master

Rpl_semi_sync_master_net_avg_wait_time

No No Yes
No Global No

DESCRIPTION: The average time the master waited for a slave reply

Rpl_semi_sync_master_net_wait_time

No No Yes
No Global No

DESCRIPTION: The total time the master waited for slave replies

Rpl_semi_sync_master_net_waits

No No Yes
No Global No

DESCRIPTION: The total number of times the master waited for slave replies

Rpl_semi_sync_master_no_times

No No Yes
No Global No

DESCRIPTION: Number of times the master turned off semisynchronous replication

Rpl_semi_sync_master_no_tx

No No Yes
No Global No

DESCRIPTION: Number of commits not acknowledged successfully

Rpl_semi_sync_master_status

No No Yes
No Global No

DESCRIPTION: Whether semisynchronous replication is operational on the master

Rpl_semi_sync_master_timefunc_failures

No No Yes
No Global No

DESCRIPTION: Number of times the master failed when calling time functions

rpl_semi_sync_master_timeout

No Yes No
No Global Yes

DESCRIPTION: Number of milliseconds to wait for slave acknowledgment

rpl_semi_sync_master_trace_level

No Yes No
No Global Yes

DESCRIPTION: The semisynchronous replication debug trace level on the master

Rpl_semi_sync_master_tx_avg_wait_time

No No Yes
No Global No

DESCRIPTION: The average time the master waited for each transaction

Rpl_semi_sync_master_tx_wait_time

No No Yes
No Global No

DESCRIPTION: The total time the master waited for transactions

Rpl_semi_sync_master_tx_waits

No No Yes
No Global No

DESCRIPTION: The total number of times the master waited for transactions

rpl_semi_sync_master_wait_for_slave_count

No Yes No
No Global Yes

DESCRIPTION: How many slave acknowledgments the master must receive per transaction before proceeding

rpl_semi_sync_master_wait_no_slave

No Yes No
No Global Yes

DESCRIPTION: Whether master waits for timeout even with no slaves

rpl_semi_sync_master_wait_point

No Yes No
No Global Yes

DESCRIPTION: The wait point for slave transaction receipt acknowledgment

Rpl_semi_sync_master_wait_pos_backtraverse

No No Yes
No Global No

DESCRIPTION: The total number of times the master waited for an event with binary coordinates lower than events waited for previously

Rpl_semi_sync_master_wait_sessions

No No Yes
No Global No

DESCRIPTION: Number of sessions currently waiting for slave replies

Rpl_semi_sync_master_yes_tx

No No Yes
No Global No

DESCRIPTION: Number of commits acknowledged successfully

rpl_semi_sync_slave_enabled

No Yes No
No Global Yes

DESCRIPTION: Whether semisynchronous replication is enabled on slave

Rpl_semi_sync_slave_status

No No Yes
No Global No

DESCRIPTION: Whether semisynchronous replication is operational on slave

rpl_semi_sync_slave_trace_level

No Yes No
No Global Yes

DESCRIPTION: The semisynchronous replication debug trace level on the slave

rpl_stop_slave_timeout

Yes Yes No
Yes Global Yes

DESCRIPTION: Set the number of seconds that STOP SLAVE waits before timing out.

server_uuid

No Yes No
No Global No

DESCRIPTION: The server's globally unique ID, automatically (re)generated at server start

show-slave-auth-info

Yes No No
Yes No

DESCRIPTION: Show user name and password in SHOW SLAVE HOSTS on this master

simplified_binlog_gtid_recovery

Yes Yes No
Yes Global No

DESCRIPTION: Controls how binary logs are iterated during GTID recovery

skip-slave-start

Yes No No
Yes No

DESCRIPTION: If set, slave is not autostarted

slave-checkpoint-group

Yes No No
Yes No

DESCRIPTION: Maximum number of transactions processed by a multi-threaded slave before a checkpoint operation is called to update progress status. Not supported by MySQL Cluster.

slave-checkpoint-period

Yes No No
Yes No

DESCRIPTION: Update progress status of multi-threaded slave and flush relay log info to disk after this number of milliseconds. Not supported by MySQL Cluster.

slave-load-tmpdir

Yes Yes No
Yes Global No

DESCRIPTION: The location where the slave should put its temporary files when replicating a LOAD DATA INFILE statement

slave-max-allowed-packet

Yes No No
Yes No

DESCRIPTION: Maximum size, in bytes, of a packet that can be sent from a replication master to a slave; overrides max_allowed_packet.

slave_net_timeout

Yes Yes No
Yes Global Yes

DESCRIPTION: Number of seconds to wait for more data from a master/slave connection before aborting the read

slave-parallel-type

Yes No No
Yes No

DESCRIPTION: Tells the slave to use database partioning (DATABASE) or timestamp information (LOGICAL_CLOCK) from the master to parallelize transactions. The default is DATABASE.

slave-parallel-workers

Yes No No
Yes No

DESCRIPTION: Number of worker threads for executing events in parallel. Set to 0 (the default) to disable slave multi-threading. Not supported by MySQL Cluster.

slave-pending-jobs-size-max

Yes No No
No No

DESCRIPTION: Maximum size of slave worker queues holding events not yet applied.

slave-rows-search-algorithms

Yes No No
Yes No

DESCRIPTION: Determines search algorithms used for slave update batching. Any 2 or 3 from the list INDEX_SEARCH, TABLE_SCAN, HASH_SCAN; the default is TABLE_SCAN,INDEX_SCAN.

slave-skip-errors

Yes Yes No
Yes Global No

DESCRIPTION: Tells the slave thread to continue replication when a query returns an error from the provided list

slave_checkpoint_group

Yes Yes No
Yes Global Yes

DESCRIPTION: Maximum number of transactions processed by a multi-threaded slave before a checkpoint operation is called to update progress status. Not supported by MySQL Cluster.

slave_checkpoint_period

Yes Yes No
Yes Global Yes

DESCRIPTION: Update progress status of multi-threaded slave and flush relay log info to disk after this number of milliseconds. Not supported by MySQL Cluster.

slave_compressed_protocol

Yes Yes No
Yes Global Yes

DESCRIPTION: Use compression on master/slave protocol

slave_exec_mode

Yes Yes No
Yes Global Yes

DESCRIPTION: Allows for switching the slave thread between IDEMPOTENT mode (key and some other errors suppressed) and STRICT mode; STRICT mode is the default, except for MySQL Cluster, where IDEMPOTENT is always used

Slave_heartbeat_period

No No Yes
No Global No

DESCRIPTION: The slave's replication heartbeat interval, in seconds

slave_max_allowed_packet

No Yes No
No Global Yes

DESCRIPTION: Maximum size, in bytes, of a packet that can be sent from a replication master to a slave; overrides max_allowed_packet.

Slave_open_temp_tables

No No Yes
No Global No

DESCRIPTION: Number of temporary tables that the slave SQL thread currently has open

slave_parallel_type

No Yes No
No Global Yes

DESCRIPTION: Tells the slave to use database partioning (DATABASE) or information (LOGICAL_CLOCK) from master to parallelize transactions. The default is DATABASE.

slave_parallel_workers

Yes Yes No
No Global Yes

DESCRIPTION: Number of worker threads for executing events in parallel. Set to 0 (the default) to disable slave multi-threading. Not supported by MySQL Cluster.

slave_pending_jobs_size_max

No Yes No
No Global Yes

DESCRIPTION: Maximum size of slave worker queues holding events not yet applied.

slave_preserve_commit_order

Yes Yes No
No Global Yes

DESCRIPTION: Ensures that all commits by slave workers happen in the same order as on the master to maintain consistency when using parallel worker threads.

Slave_retried_transactions

No No Yes
No Global No

DESCRIPTION: The total number of times since startup that the replication slave SQL thread has retried transactions

slave_rows_search_algorithms

No Yes No
No Global Yes

DESCRIPTION: Determines search algorithms used for slave update batching. Any 2 or 3 from the list INDEX_SEARCH, TABLE_SCAN, HASH_SCAN; the default is TABLE_SCAN,INDEX_SCAN.

Slave_running

No No Yes
No Global No

DESCRIPTION: The state of this server as a replication slave (slave I/O thread status)

slave_transaction_retries

Yes Yes No
Yes Global Yes

DESCRIPTION: Number of times the slave SQL thread will retry a transaction in case it failed with a deadlock or elapsed lock wait timeout, before giving up and stopping

slave_type_conversions

Yes Yes No
Yes Global No

DESCRIPTION: Controls type conversion mode on replication slave. Value is a list of zero or more elements from the list: ALL_LOSSY, ALL_NON_LOSSY. Set to an empty string to disallow type conversions between master and slave.

sql_slave_skip_counter

No Yes No
No Global Yes

DESCRIPTION: Number of events from the master that a slave server should skip. Not compatible with GTID replication.

sync_binlog

Yes Yes No
Yes Global Yes

DESCRIPTION: Synchronously flush binary log to disk after every #th event

sync_master_info

Yes Yes No
Yes Global Yes

DESCRIPTION: Synchronize master.info to disk after every #th event.

sync_relay_log

Yes Yes No
Yes Global Yes

DESCRIPTION: Synchronize relay log to disk after every #th event.

sync_relay_log_info

Yes Yes No
Yes Global Yes

DESCRIPTION: Synchronize relay.info file to disk after every #th event.


Section 18.1.6.2, “Replication Master Options and Variables”, provides more detailed information about options and variables relating to replication master servers. For more information about options and variables relating to replication slaves, see Section 18.1.6.3, “Replication Slave Options and Variables”.

Table 18.4 Summary of Binary Logging options and variables in MySQL 5.7

Option or Variable Name
Command Line System Variable Status Variable
Option File Scope Dynamic
Notes

binlog-checksum

Yes No No
Yes No

DESCRIPTION: Enable/disable binary log checksums

binlog-do-db

Yes No No
Yes No

DESCRIPTION: Limits binary logging to specific databases

binlog_format

Yes Yes No
Yes Both Yes

DESCRIPTION: Specifies the format of the binary log

binlog-ignore-db

Yes No No
Yes No

DESCRIPTION: Tells the master that updates to the given database should not be logged to the binary log

binlog-row-event-max-size

Yes No No
Yes No

DESCRIPTION: Binary log max event size

binlog-rows-query-log-events

Yes No No
Yes No

DESCRIPTION: Enables logging of rows query log events when using row-based logging. Disabled by default. Do not enable when producing logs for pre-5.6.2 slaves/readers.

Binlog_cache_disk_use

No No Yes
No Global No

DESCRIPTION: Number of transactions that used a temporary file instead of the binary log cache

binlog_cache_size

Yes Yes No
Yes Global Yes

DESCRIPTION: Size of the cache to hold the SQL statements for the binary log during a transaction

Binlog_cache_use

No No Yes
No Global No

DESCRIPTION: Number of transactions that used the temporary binary log cache

binlog_checksum

No Yes No
No Global Yes

DESCRIPTION: Enable/disable binary log checksums

binlog_direct_non_transactional_updates

Yes Yes No
Yes Both Yes

DESCRIPTION: Causes updates using statement format to nontransactional engines to be written directly to binary log. See documentation before using.

binlog_error_action

Yes Yes No
Yes Both Yes

DESCRIPTION: Controls what happens when the server cannot write to the binary log.

binlog_group_commit_sync_delay

Yes Yes No
Yes Global Yes

DESCRIPTION: Sets the number of microseconds to wait before synchronizing transactions to disk.

binlog_group_commit_sync_no_delay_count

Yes Yes No
Yes Global Yes

DESCRIPTION: Sets the maximum number of transactions to wait for before aborting the current delay specified by binlog_group_commit_sync_delay.

binlog_max_flush_queue_time

No Yes No
No Global Yes

DESCRIPTION: How long to read transactions before flushing to binary log

binlog_order_commits

No Yes No
No Global Yes

DESCRIPTION: Whether to commit in same order as writes to binary log

binlog_row_image

Yes Yes No
Yes Both Yes

DESCRIPTION: Use full or minimal images when logging row changes. Allowed values are full, minimal, and noblob.

binlog_rows_query_log_events

No Yes No
No Both Yes

DESCRIPTION: When TRUE, enables logging of rows query log events in row-based logging mode. FALSE by default. Do not enable when producing logs for pre-5.6.2 replication slaves or other readers.

Binlog_stmt_cache_disk_use

No No Yes
No Global No

DESCRIPTION: Number of nontransactional statements that used a temporary file instead of the binary log statement cache

binlog_stmt_cache_size

Yes Yes No
Yes Global Yes

DESCRIPTION: Size of the cache to hold nontransactional statements for the binary log during a transaction

Binlog_stmt_cache_use

No No Yes
No Global No

DESCRIPTION: Number of statements that used the temporary binary log statement cache

binlogging_impossible_mode

Yes Yes No
Yes Both Yes

DESCRIPTION: Deprecated and will be removed in a future version. Use the renamed binlog_error_action instead.

Com_show_binlog_events

No No Yes
No Both No

DESCRIPTION: Count of SHOW BINLOG EVENTS statements

Com_show_binlogs

No No Yes
No Both No

DESCRIPTION: Count of SHOW BINLOGS statements

log-bin-use-v1-row-events

Yes Yes No
Yes Global No

DESCRIPTION: Use version 1 binary log row events

log_bin_basename

No Yes No
No Global No

DESCRIPTION: Complete path to binary log, including filename

log_bin_use_v1_row_events

Yes Yes No
Yes Global No

DESCRIPTION: Shows whether server is using version 1 binary log row events

master-verify-checksum

Yes No No
Yes No

DESCRIPTION: Cause master to examine checksums when reading from the binary log

master_verify_checksum

No Yes No
No Global Yes

DESCRIPTION: Cause master to read checksums from binary log.

max-binlog-dump-events

Yes No No
Yes No

DESCRIPTION: Option used by mysql-test for debugging and testing of replication

max_binlog_cache_size

Yes Yes No
Yes Global Yes

DESCRIPTION: Can be used to restrict the total size used to cache a multi-statement transaction

max_binlog_size

Yes Yes No
Yes Global Yes

DESCRIPTION: Binary log will be rotated automatically when size exceeds this value

max_binlog_stmt_cache_size

Yes Yes No
Yes Global Yes

DESCRIPTION: Can be used to restrict the total size used to cache all nontransactional statements during a transaction

slave-sql-verify-checksum

Yes No No
Yes No

DESCRIPTION: Cause slave to examine checksums when reading from the relay log

slave_sql_verify_checksum

No Yes No
No Global Yes

DESCRIPTION: Cause slave to examine checksums when reading from relay log.

sporadic-binlog-dump-fail

Yes No No
Yes No

DESCRIPTION: Option used by mysql-test for debugging and testing of replication


Section 18.1.6.4, “Binary Logging Options and Variables”, provides more detailed information about options and variables relating to binary logging. For additional general information about the binary log, see Section 6.4.4, “The Binary Log”.

For information about the sql_log_bin and sql_log_off variables, see Section 6.1.5, “Server System Variables”.

For a table showing all command-line options, system and status variables used with mysqld, see Section 6.1.3, “Server Option and Variable Reference”.

18.1.6.2 Replication Master Options and Variables

This section describes the server options and system variables that you can use on replication master servers. You can specify the options either on the command line or in an option file. You can specify system variable values using SET.

On the master and each slave, you must use the server-id option to establish a unique replication ID. For each server, you should pick a unique positive integer in the range from 1 to 232 − 1, and each ID must be different from every other ID in use by any other replication master or slave. Example: server-id=3.

For options used on the master for controlling binary logging, see Section 18.1.6.4, “Binary Logging Options and Variables”.

System Variables Used on Replication Masters

The following system variables are used to control replication masters:

  • auto_increment_increment

    System VariableNameauto_increment_increment
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default1
    Min Value1
    Max Value65535

    auto_increment_increment and auto_increment_offset are intended for use with master-to-master replication, and can be used to control the operation of AUTO_INCREMENT columns. Both variables have global and session values, and each can assume an integer value between 1 and 65,535 inclusive. Setting the value of either of these two variables to 0 causes its value to be set to 1 instead. Attempting to set the value of either of these two variables to an integer greater than 65,535 or less than 0 causes its value to be set to 65,535 instead. Attempting to set the value of auto_increment_increment or auto_increment_offset to a noninteger value produces an error, and the actual value of the variable remains unchanged.

    Note

    auto_increment_increment is also supported for use with NDB tables.

    These two variables affect AUTO_INCREMENT column behavior as follows:

    • auto_increment_increment controls the interval between successive column values. For example:

      mysql> SHOW VARIABLES LIKE 'auto_inc%';
      +--------------------------+-------+
      | Variable_name            | Value |
      +--------------------------+-------+
      | auto_increment_increment | 1     |
      | auto_increment_offset    | 1     |
      +--------------------------+-------+
      2 rows in set (0.00 sec)
      
      mysql> CREATE TABLE autoinc1
          -> (col INT NOT NULL AUTO_INCREMENT PRIMARY KEY);
        Query OK, 0 rows affected (0.04 sec)
      
      mysql> SET @@auto_increment_increment=10;
      Query OK, 0 rows affected (0.00 sec)
      
      mysql> SHOW VARIABLES LIKE 'auto_inc%';
      +--------------------------+-------+
      | Variable_name            | Value |
      +--------------------------+-------+
      | auto_increment_increment | 10    |
      | auto_increment_offset    | 1     |
      +--------------------------+-------+
      2 rows in set (0.01 sec)
      
      mysql> INSERT INTO autoinc1 VALUES (NULL), (NULL), (NULL), (NULL);
      Query OK, 4 rows affected (0.00 sec)
      Records: 4  Duplicates: 0  Warnings: 0
      
      mysql> SELECT col FROM autoinc1;
      +-----+
      | col |
      +-----+
      |   1 |
      |  11 |
      |  21 |
      |  31 |
      +-----+
      4 rows in set (0.00 sec)
      
    • auto_increment_offset determines the starting point for the AUTO_INCREMENT column value. Consider the following, assuming that these statements are executed during the same session as the example given in the description for auto_increment_increment:

      mysql> SET @@auto_increment_offset=5;
      Query OK, 0 rows affected (0.00 sec)
      
      mysql> SHOW VARIABLES LIKE 'auto_inc%';
      +--------------------------+-------+
      | Variable_name            | Value |
      +--------------------------+-------+
      | auto_increment_increment | 10    |
      | auto_increment_offset    | 5     |
      +--------------------------+-------+
      2 rows in set (0.00 sec)
      
      mysql> CREATE TABLE autoinc2
          -> (col INT NOT NULL AUTO_INCREMENT PRIMARY KEY);
      Query OK, 0 rows affected (0.06 sec)
      
      mysql> INSERT INTO autoinc2 VALUES (NULL), (NULL), (NULL), (NULL);
      Query OK, 4 rows affected (0.00 sec)
      Records: 4  Duplicates: 0  Warnings: 0
      
      mysql> SELECT col FROM autoinc2;
      +-----+
      | col |
      +-----+
      |   5 |
      |  15 |
      |  25 |
      |  35 |
      +-----+
      4 rows in set (0.02 sec)
      

      When the value of auto_increment_offset is greater than that of auto_increment_increment, the value of auto_increment_offset is ignored.

    If either of these variables is changed, and then new rows inserted into a table containing an AUTO_INCREMENT column, the results may seem counterintuitive because the series of AUTO_INCREMENT values is calculated without regard to any values already present in the column, and the next value inserted is the least value in the series that is greater than the maximum existing value in the AUTO_INCREMENT column. The series is calculated like this:

    auto_increment_offset + N × auto_increment_increment

    where N is a positive integer value in the series [1, 2, 3, ...]. For example:

    mysql> SHOW VARIABLES LIKE 'auto_inc%';
    +--------------------------+-------+
    | Variable_name            | Value |
    +--------------------------+-------+
    | auto_increment_increment | 10    |
    | auto_increment_offset    | 5     |
    +--------------------------+-------+
    2 rows in set (0.00 sec)
    
    mysql> SELECT col FROM autoinc1;
    +-----+
    | col |
    +-----+
    |   1 |
    |  11 |
    |  21 |
    |  31 |
    +-----+
    4 rows in set (0.00 sec)
    
    mysql> INSERT INTO autoinc1 VALUES (NULL), (NULL), (NULL), (NULL);
    Query OK, 4 rows affected (0.00 sec)
    Records: 4  Duplicates: 0  Warnings: 0
    
    mysql> SELECT col FROM autoinc1;
    +-----+
    | col |
    +-----+
    |   1 |
    |  11 |
    |  21 |
    |  31 |
    |  35 |
    |  45 |
    |  55 |
    |  65 |
    +-----+
    8 rows in set (0.00 sec)
    

    The values shown for auto_increment_increment and auto_increment_offset generate the series 5 + N × 10, that is, [5, 15, 25, 35, 45, ...]. The highest value present in the col column prior to the INSERT is 31, and the next available value in the AUTO_INCREMENT series is 35, so the inserted values for col begin at that point and the results are as shown for the SELECT query.

    It is not possible to restrict the effects of these two variables to a single table; these variables control the behavior of all AUTO_INCREMENT columns in all tables on the MySQL server. If the global value of either variable is set, its effects persist until the global value is changed or overridden by setting the session value, or until mysqld is restarted. If the local value is set, the new value affects AUTO_INCREMENT columns for all tables into which new rows are inserted by the current user for the duration of the session, unless the values are changed during that session.

    The default value of auto_increment_increment is 1. See Section 18.4.1.1, “Replication and AUTO_INCREMENT”.

  • auto_increment_offset

    System VariableNameauto_increment_offset
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default1
    Min Value1
    Max Value65535

    This variable has a default value of 1. For more information, see the description for auto_increment_increment.

    Note

    auto_increment_offset is also supported for use with NDB tables.

18.1.6.3 Replication Slave Options and Variables

This section explains the server options and system variables that apply to slave replication servers and contains the following:

Startup Options for Replication Slaves

Options for Logging Slave Status to Tables

System Variables Used on Replication Slaves

Specify the options either on the command line or in an option file. Many of the options can be set while the server is running by using the CHANGE MASTER TO statement. Specify system variable values using SET.

Server ID.  On the master and each slave, you must use the server-id option to establish a unique replication ID in the range from 1 to 232 − 1. Unique means that each ID must be different from every other ID in use by any other replication master or slave. Example my.cnf file:

[mysqld]
server-id=3
Startup Options for Replication Slaves

This section explains startup options for controlling replication slave servers. Many of these options can be set while the server is running by using the CHANGE MASTER TO statement. Others, such as the --replicate-* options, can be set only when the slave server starts. Replication-related system variables are discussed later in this section.

  • --log-slave-updates

    Command-Line Format--log-slave-updates
    System VariableNamelog_slave_updates
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeboolean
    DefaultOFF

    Normally, a slave does not write any updates that are received from a master server to its own binary log. This option causes the slave to write the updates performed by its SQL thread to its own binary log. For this option to have any effect, the slave must also be started with the --log-bin option to enable binary logging. --log-slave-updates is used when you want to chain replication servers. For example, you might want to set up replication servers using this arrangement:

    A -> B -> C
    

    Here, A serves as the master for the slave B, and B serves as the master for the slave C. For this to work, B must be both a master and a slave. You must start both A and B with --log-bin to enable binary logging, and B with the --log-slave-updates option so that updates received from A are logged by B to its binary log.

  • --log-slow-slave-statements

    Removed5.7.1
    Command-Line Format--log-slow-slave-statements (5.7.0)
    Permitted ValuesTypeboolean
    DefaultOFF

    When the slow query log is enabled, this option enables logging for queries that have taken more than long_query_time seconds to execute on the slave.

    This command-line option was removed in MySQL 5.7.1 and replaced by the log_slow_slave_statements system variable. The system variable can be set on the command line or in option files the same way as the option, so there is no need for any changes at server startup, but the system variable also makes it possible to examine or set the value at runtime.

  • --log-warnings[=level]

    Deprecated5.7.2
    Command-Line Format--log-warnings[=#]
    System VariableNamelog_warnings
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (32-bit platforms, <= 5.7.1)Typeinteger
    Default1
    Min Value0
    Max Value4294967295
    Permitted Values (32-bit platforms, >= 5.7.2)Typeinteger
    Default2
    Min Value0
    Max Value4294967295
    Permitted Values (64-bit platforms, <= 5.7.1)Typeinteger
    Default1
    Min Value0
    Max Value18446744073709551615
    Permitted Values (64-bit platforms, >= 5.7.2)Typeinteger
    Default2
    Min Value0
    Max Value18446744073709551615
    Note

    As of MySQL 5.7.2, the log_error_verbosity system variable is preferred over, and should be used instead of, the --log-warnings option or log_warnings system variable. For more information, see the descriptions of log_error_verbosity and log_warnings. The --log-warnings command-line option and log_warnings system variable are deprecated and will be removed in a future MySQL release.

    Causes the server to record more messages to the error log about what it is doing. With respect to replication, the server generates warnings that it succeeded in reconnecting after a network or connection failure, and provides information about how each slave thread started. This variable is enabled by default (the default is 1 before MySQL 5.7.2, 2 as of 5.7.2). To disable it, set it to 0. The server logs messages about statements that are unsafe for statement-based logging if the value is greater than 0. Aborted connections and access-denied errors for new connection attempts are logged if the value is greater than 1. See Section B.5.2.11, “Communication Errors and Aborted Connections”.

    Note

    The effects of this option are not limited to replication. It produces warnings across a spectrum of server activities.

  • --master-info-file=file_name

    Command-Line Format--master-info-file=file_name
    Permitted ValuesTypefile name
    Defaultmaster.info

    The name to use for the file in which the slave records information about the master. The default name is master.info in the data directory. For information about the format of this file, see Section 18.2.4.2, “Slave Status Logs”.

  • --master-retry-count=count

    Deprecated5.6.1
    Command-Line Format--master-retry-count=#
    Permitted Values (32-bit platforms)Typeinteger
    Default86400
    Min Value0
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default86400
    Min Value0
    Max Value18446744073709551615

    The number of times that the slave tries to connect to the master before giving up. Reconnects are attempted at intervals set by the MASTER_CONNECT_RETRY option of the CHANGE MASTER TO statement (default 60). Reconnects are triggered when data reads by the slave time out according to the --slave-net-timeout option. The default value is 86400. A value of 0 means infinite; the slave attempts to connect forever.

    This option is deprecated and will be removed in a future MySQL release. Applications should be updated to use the MASTER_RETRY_COUNT option of the CHANGE MASTER TO statement instead.

  • --max-relay-log-size=size

    Command-Line Format--max_relay_log_size=#
    System VariableNamemax_relay_log_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0
    Min Value0
    Max Value1073741824

    The size at which the server rotates relay log files automatically. If this value is nonzero, the relay log is rotated automatically when its size exceeds this value. If this value is zero (the default), the size at which relay log rotation occurs is determined by the value of max_binlog_size. For more information, see Section 18.2.4.1, “The Slave Relay Log”.

  • --relay-log=file_name

    Command-Line Format--relay-log=file_name
    System VariableNamerelay_log
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypefile name

    The base name for the relay log. For the default replication channel, the default base name for relay logs is host_name-relay-bin. For non-default replication channels, the default base name for relay logs is host_name-channel-relay-bin, where channel is the name of the replication channel recorded in this relay log. The server writes the file in the data directory unless the base name is given with a leading absolute path name to specify a different directory. The server creates relay log files in sequence by adding a numeric suffix to the base name.

    Due to the manner in which MySQL parses server options, if you specify this option, you must supply a value; the default base name is used only if the option is not actually specified. If you use the --relay-log option without specifying a value, unexpected behavior is likely to result; this behavior depends on the other options used, the order in which they are specified, and whether they are specified on the command line or in an option file. For more information about how MySQL handles server options, see Section 5.2.3, “Specifying Program Options”.

    If you specify this option, the value specified is also used as the base name for the relay log index file. You can override this behavior by specifying a different relay log index file base name using the --relay-log-index option.

    When the server reads an entry from the index file, it checks whether the entry contains a relative path. If it does, the relative part of the path is replaced with the absolute path set using the --relay-log option. An absolute path remains unchanged; in such a case, the index must be edited manually to enable the new path or paths to be used. Previously, manual intervention was required whenever relocating the binary log or relay log files. (Bug #11745230, Bug #12133)

    You may find the --relay-log option useful in performing the following tasks:

    • Creating relay logs whose names are independent of host names.

    • If you need to put the relay logs in some area other than the data directory because your relay logs tend to be very large and you do not want to decrease max_relay_log_size.

    • To increase speed by using load-balancing between disks.

    You can obtain the relay log file name (and path) from the relay_log_basename system variable.

  • --relay-log-index=file_name

    Command-Line Format--relay-log-index=file_name
    System VariableNamerelay_log_index
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypefile name

    The name to use for the relay log index file. The default name is host_name-relay-bin.index in the data directory, where host_name is the name of the server. For the default replication channel, the default name is host_name-relay-bin.index. For non-default replication channels, the default name is host_name-channel-relay-bin.index, where channel is the name of the replication channel recorded in this relay log index.

    Due to the manner in which MySQL parses server options, if you specify this option, you must supply a value; the default base name is used only if the option is not actually specified. If you use the --relay-log-index option without specifying a value, unexpected behavior is likely to result; this behavior depends on the other options used, the order in which they are specified, and whether they are specified on the command line or in an option file. For more information about how MySQL handles server options, see Section 5.2.3, “Specifying Program Options”.

    If you specify this option, the value specified is also used as the base name for the relay logs. You can override this behavior by specifying a different relay log file base name using the --relay-log option.

  • --relay-log-info-file=file_name

    Command-Line Format--relay-log-info-file=file_name
    Permitted ValuesTypefile name
    Defaultrelay-log.info

    The name to use for the file in which the slave records information about the relay logs. The default name is relay-log.info in the data directory. For information about the format of this file, see Section 18.2.4.2, “Slave Status Logs”.

  • --relay-log-purge={0|1}

    Command-Line Format--relay_log_purge
    System VariableNamerelay_log_purge
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultTRUE

    Disable or enable automatic purging of relay logs as soon as they are no longer needed. The default value is 1 (enabled). This is a global variable that can be changed dynamically with SET GLOBAL relay_log_purge = N. Disabling purging of relay logs when using the --relay-log-recovery option puts data consistency at risk.

  • --relay-log-recovery={0|1}

    Command-Line Format--relay-log-recovery
    Permitted ValuesTypeboolean
    DefaultFALSE

    Enables automatic relay log recovery immediately following server startup. The recovery process creates a new relay log file, initializes the SQL thread position to this new relay log, and initializes the I/O thread to the SQL thread position. Reading of the relay log from the master then continues. This should be used following an unexpected halt of a replication slave to ensure that no possibly corrupted relay logs are processed. The default value is 0 (disabled).

    This variable can be set to 1 to make a slave resilient to unexpected halts, see Section 18.3.2, “Handling an Unexpected Halt of a Replication Slave” for more information. Enabling the --relay-log-recovery option when relay-log-purge is disabled risks reading the relay log from files that were not purged, leading to data inconsistency.

    When using a multi-threaded slave (in other words slave_parallel_workers is greater than 0), inconsistencies such as gaps can occur in the sequence of transactions that have been executed from the relay log. Enabling the --relay-log-recovery option when there are inconsistencies causes an error and the option has no effect. The solution in this situation is to issue START SLAVE UNTIL SQL_AFTER_MTS_GAPS, which brings the server to a more consistent state, then issue RESET SLAVE to remove the relay logs. See Section 18.4.1.34, “Replication and Transaction Inconsistencies” for more information.

  • --relay-log-space-limit=size

    Command-Line Format--relay_log_space_limit=#
    System VariableNamerelay_log_space_limit
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted Values (32-bit platforms)Typeinteger
    Default0
    Min Value0
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default0
    Min Value0
    Max Value18446744073709551615

    This option places an upper limit on the total size in bytes of all relay logs on the slave. A value of 0 means no limit. This is useful for a slave server host that has limited disk space. When the limit is reached, the I/O thread stops reading binary log events from the master server until the SQL thread has caught up and deleted some unused relay logs. Note that this limit is not absolute: There are cases where the SQL thread needs more events before it can delete relay logs. In that case, the I/O thread exceeds the limit until it becomes possible for the SQL thread to delete some relay logs because not doing so would cause a deadlock. You should not set --relay-log-space-limit to less than twice the value of --max-relay-log-size (or --max-binlog-size if --max-relay-log-size is 0). In that case, there is a chance that the I/O thread waits for free space because --relay-log-space-limit is exceeded, but the SQL thread has no relay log to purge and is unable to satisfy the I/O thread. This forces the I/O thread to ignore --relay-log-space-limit temporarily.

  • --replicate-do-db=db_name

    Command-Line Format--replicate-do-db=name
    Permitted ValuesTypestring

    Creates a replication filter using the name of a database. In MySQL 5.7.3 and later, such filters can also be created using CHANGE REPLICATION FILTER REPLICATE_DO_DB. The precise effect of this filtering depends on whether statement-based or row-based replication is in use, and are described in the next several paragraphs.

    Statement-based replication.  Tell the slave SQL thread to restrict replication to statements where the default database (that is, the one selected by USE) is db_name. To specify more than one database, use this option multiple times, once for each database; however, doing so does not replicate cross-database statements such as UPDATE some_db.some_table SET foo='bar' while a different database (or no database) is selected.

    Warning

    To specify multiple databases you must use multiple instances of this option. Because database names can contain commas, if you supply a comma separated list then the list will be treated as the name of a single database.

    An example of what does not work as you might expect when using statement-based replication: If the slave is started with --replicate-do-db=sales and you issue the following statements on the master, the UPDATE statement is not replicated:

    USE prices;
    UPDATE sales.january SET amount=amount+1000;
    

    The main reason for this check just the default database behavior is that it is difficult from the statement alone to know whether it should be replicated (for example, if you are using multiple-table DELETE statements or multiple-table UPDATE statements that act across multiple databases). It is also faster to check only the default database rather than all databases if there is no need.

    Row-based replication.  Tells the slave SQL thread to restrict replication to database db_name. Only tables belonging to db_name are changed; the current database has no effect on this. Suppose that the slave is started with --replicate-do-db=sales and row-based replication is in effect, and then the following statements are run on the master:

    USE prices;
    UPDATE sales.february SET amount=amount+100;
    

    The february table in the sales database on the slave is changed in accordance with the UPDATE statement; this occurs whether or not the USE statement was issued. However, issuing the following statements on the master has no effect on the slave when using row-based replication and --replicate-do-db=sales:

    USE prices;
    UPDATE prices.march SET amount=amount-25;
    

    Even if the statement USE prices were changed to USE sales, the UPDATE statement's effects would still not be replicated.

    Another important difference in how --replicate-do-db is handled in statement-based replication as opposed to row-based replication occurs with regard to statements that refer to multiple databases. Suppose that the slave is started with --replicate-do-db=db1, and the following statements are executed on the master:

    USE db1;
    UPDATE db1.table1 SET col1 = 10, db2.table2 SET col2 = 20;
    

    If you are using statement-based replication, then both tables are updated on the slave. However, when using row-based replication, only table1 is affected on the slave; since table2 is in a different database, table2 on the slave is not changed by the UPDATE. Now suppose that, instead of the USE db1 statement, a USE db4 statement had been used:

    USE db4;
    UPDATE db1.table1 SET col1 = 10, db2.table2 SET col2 = 20;
    

    In this case, the UPDATE statement would have no effect on the slave when using statement-based replication. However, if you are using row-based replication, the UPDATE would change table1 on the slave, but not table2—in other words, only tables in the database named by --replicate-do-db are changed, and the choice of default database has no effect on this behavior.

    If you need cross-database updates to work, use --replicate-wild-do-table=db_name.% instead. See Section 18.2.5, “How Servers Evaluate Replication Filtering Rules”.

    Note

    This option affects replication in the same manner that --binlog-do-db affects binary logging, and the effects of the replication format on how --replicate-do-db affects replication behavior are the same as those of the logging format on the behavior of --binlog-do-db.

    This option has no effect on BEGIN, COMMIT, or ROLLBACK statements.

  • --replicate-ignore-db=db_name

    Command-Line Format--replicate-ignore-db=name
    Permitted ValuesTypestring

    Creates a replication filter using the name of a database. In MySQL 5.7.3 and later, such filters can also be created using CHANGE REPLICATION FILTER REPLICATE_IGNORE_DB. As with --replicate-do-db, the precise effect of this filtering depends on whether statement-based or row-based replication is in use, and are described in the next several paragraphs.

    Statement-based replication.  Tells the slave SQL thread not to replicate any statement where the default database (that is, the one selected by USE) is db_name.

    Row-based replication.  Tells the slave SQL thread not to update any tables in the database db_name. The default database has no effect.

    When using statement-based replication, the following example does not work as you might expect. Suppose that the slave is started with --replicate-ignore-db=sales and you issue the following statements on the master:

    USE prices;
    UPDATE sales.january SET amount=amount+1000;
    

    The UPDATE statement is replicated in such a case because --replicate-ignore-db applies only to the default database (determined by the USE statement). Because the sales database was specified explicitly in the statement, the statement has not been filtered. However, when using row-based replication, the UPDATE statement's effects are not propagated to the slave, and the slave's copy of the sales.january table is unchanged; in this instance, --replicate-ignore-db=sales causes all changes made to tables in the master's copy of the sales database to be ignored by the slave.

    To specify more than one database to ignore, use this option multiple times, once for each database. Because database names can contain commas, if you supply a comma separated list then the list will be treated as the name of a single database.

    You should not use this option if you are using cross-database updates and you do not want these updates to be replicated. See Section 18.2.5, “How Servers Evaluate Replication Filtering Rules”.

    If you need cross-database updates to work, use --replicate-wild-ignore-table=db_name.% instead. See Section 18.2.5, “How Servers Evaluate Replication Filtering Rules”.

    Note

    This option affects replication in the same manner that --binlog-ignore-db affects binary logging, and the effects of the replication format on how --replicate-ignore-db affects replication behavior are the same as those of the logging format on the behavior of --binlog-ignore-db.

    This option has no effect on BEGIN, COMMIT, or ROLLBACK statements.

  • --replicate-do-table=db_name.tbl_name

    Command-Line Format--replicate-do-table=name
    Permitted ValuesTypestring

    Creates a replication filter by telling the slave SQL thread to restrict replication to a given table. To specify more than one table, use this option multiple times, once for each table. This works for both cross-database updates and default database updates, in contrast to --replicate-do-db. See Section 18.2.5, “How Servers Evaluate Replication Filtering Rules”.

    In MySQL 5.7.3 and later, you can also create such a filter by issuing a CHANGE REPLICATION FILTER REPLICATE_DO_TABLE statement.

    This option affects only statements that apply to tables. It does not affect statements that apply only to other database objects, such as stored routines. To filter statements operating on stored routines, use one or more of the --replicate-*-db options.

  • --replicate-ignore-table=db_name.tbl_name

    Command-Line Format--replicate-ignore-table=name
    Permitted ValuesTypestring

    Creates a replication filter by telling the slave SQL thread not to replicate any statement that updates the specified table, even if any other tables might be updated by the same statement. To specify more than one table to ignore, use this option multiple times, once for each table. This works for cross-database updates, in contrast to --replicate-ignore-db. See Section 18.2.5, “How Servers Evaluate Replication Filtering Rules”.

    In MySQL 5.7.3 and later, you can also create such a filter by issuing a CHANGE REPLICATION FILTER REPLICATE_IGNORE_TABLE statement.

    This option affects only statements that apply to tables. It does not affect statements that apply only to other database objects, such as stored routines. To filter statements operating on stored routines, use one or more of the --replicate-*-db options.

  • --replicate-rewrite-db=from_name->to_name

    Command-Line Format--replicate-rewrite-db=old_name->new_name
    Permitted ValuesTypestring

    Tells the slave to create a replication filter that translates the default database (that is, the one selected by USE) to to_name if it was from_name on the master. Only statements involving tables are affected (not statements such as CREATE DATABASE, DROP DATABASE, and ALTER DATABASE), and only if from_name is the default database on the master. To specify multiple rewrites, use this option multiple times. The server uses the first one with a from_name value that matches. The database name translation is done before the --replicate-* rules are tested.

    In MySQL 5.7.3 and later, you can also create such a filter by issuing a CHANGE REPLICATION FILTER REPLICATE_REWRITE_DB statement.

    Statements in which table names are qualified with database names when using this option do not work with table-level replication filtering options such as --replicate-do-table. Suppose we have a database named a on the master, one named b on the slave, each containing a table t, and have started the master with --replicate-rewrite-db='a->b'. At a later point in time, we execute DELETE FROM a.t. In this case, no relevant filtering rule works, for the reasons shown here:

    1. --replicate-do-table=a.t does not work because the slave has table t in database b.

    2. --replicate-do-table=b.t does not match the original statement and so is ignored.

    3. --replicate-do-table=*.t is handled identically to --replicate-do-table=a.t, and thus does not work, either.

    Similarly, the --replication-rewrite-db option does not work with cross-database updates.

    If you use this option on the command line and the > character is special to your command interpreter, quote the option value. For example:

    shell> mysqld --replicate-rewrite-db="olddb->newdb"
    
  • --replicate-same-server-id

    Command-Line Format--replicate-same-server-id
    Permitted ValuesTypeboolean
    DefaultFALSE

    To be used on slave servers. Usually you should use the default setting of 0, to prevent infinite loops caused by circular replication. If set to 1, the slave does not skip events having its own server ID. Normally, this is useful only in rare configurations. Cannot be set to 1 if --log-slave-updates is used. By default, the slave I/O thread does not write binary log events to the relay log if they have the slave's server ID (this optimization helps save disk usage). If you want to use --replicate-same-server-id, be sure to start the slave with this option before you make the slave read its own events that you want the slave SQL thread to execute.

  • --replicate-wild-do-table=db_name.tbl_name

    Command-Line Format--replicate-wild-do-table=name
    Permitted ValuesTypestring

    Creates a replication filter by telling the slave thread to restrict replication to statements where any of the updated tables match the specified database and table name patterns. Patterns can contain the % and _ wildcard characters, which have the same meaning as for the LIKE pattern-matching operator. To specify more than one table, use this option multiple times, once for each table. This works for cross-database updates. See Section 18.2.5, “How Servers Evaluate Replication Filtering Rules”.

    In MySQL 5.7.3 and later, you can also create such a filter by issuing a CHANGE REPLICATION FILTER REPLICATE_WILD_DO_TABLE statement.

    This option applies to tables, views, and triggers. It does not apply to stored procedures and functions, or events. To filter statements operating on the latter objects, use one or more of the --replicate-*-db options.

    Example: --replicate-wild-do-table=foo%.bar% replicates only updates that use a table where the database name starts with foo and the table name starts with bar.

    If the table name pattern is %, it matches any table name and the option also applies to database-level statements (CREATE DATABASE, DROP DATABASE, and ALTER DATABASE). For example, if you use --replicate-wild-do-table=foo%.%, database-level statements are replicated if the database name matches the pattern foo%.

    To include literal wildcard characters in the database or table name patterns, escape them with a backslash. For example, to replicate all tables of a database that is named my_own%db, but not replicate tables from the my1ownAABCdb database, you should escape the _ and % characters like this: --replicate-wild-do-table=my\_own\%db. If you use the option on the command line, you might need to double the backslashes or quote the option value, depending on your command interpreter. For example, with the bash shell, you would need to type --replicate-wild-do-table=my\\_own\\%db.

  • --replicate-wild-ignore-table=db_name.tbl_name

    Command-Line Format--replicate-wild-ignore-table=name
    Permitted ValuesTypestring

    Creates a replication filter which keeps the slave thread from replicating a statement in which any table matches the given wildcard pattern. To specify more than one table to ignore, use this option multiple times, once for each table. This works for cross-database updates. See Section 18.2.5, “How Servers Evaluate Replication Filtering Rules”.

    In MySQL 5.7.3 and later, you can also create such a filter by issuing a CHANGE REPLICATION FILTER REPLICATE_WILD_IGNORE_TABLE statement.

    Example: --replicate-wild-ignore-table=foo%.bar% does not replicate updates that use a table where the database name starts with foo and the table name starts with bar.

    For information about how matching works, see the description of the --replicate-wild-do-table option. The rules for including literal wildcard characters in the option value are the same as for --replicate-wild-ignore-table as well.

  • --report-host=host_name

    Command-Line Format--report-host=host_name
    System VariableNamereport_host
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring

    The host name or IP address of the slave to be reported to the master during slave registration. This value appears in the output of SHOW SLAVE HOSTS on the master server. Leave the value unset if you do not want the slave to register itself with the master.

    Note

    It is not sufficient for the master to simply read the IP address of the slave from the TCP/IP socket after the slave connects. Due to NAT and other routing issues, that IP may not be valid for connecting to the slave from the master or other hosts.

  • --report-password=password

    Command-Line Format--report-password=name
    System VariableNamereport_password
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring

    The account password of the slave to be reported to the master during slave registration. This value appears in the output of SHOW SLAVE HOSTS on the master server if the --show-slave-auth-info option is given.

    Although the name of this option might imply otherwise, --report-password is not connected to the MySQL user privilege system and so is not necessarily (or even likely to be) the same as the password for the MySQL replication user account.

  • --report-port=slave_port_num

    Command-Line Format--report-port=#
    System VariableNamereport_port
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeinteger
    Default[slave_port]
    Min Value0
    Max Value65535

    The TCP/IP port number for connecting to the slave, to be reported to the master during slave registration. Set this only if the slave is listening on a nondefault port or if you have a special tunnel from the master or other clients to the slave. If you are not sure, do not use this option.

    The default value for this option is the port number actually used by the slave (Bug #13333431). This is also the default value displayed by SHOW SLAVE HOSTS.

  • --report-user=user_name

    Command-Line Format--report-user=name
    System VariableNamereport_user
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring

    The account user name of the slave to be reported to the master during slave registration. This value appears in the output of SHOW SLAVE HOSTS on the master server if the --show-slave-auth-info option is given.

    Although the name of this option might imply otherwise, --report-user is not connected to the MySQL user privilege system and so is not necessarily (or even likely to be) the same as the name of the MySQL replication user account.

  • --show-slave-auth-info

    Command-Line Format--show-slave-auth-info
    Permitted ValuesTypeboolean
    DefaultFALSE

    Display slave user names and passwords in the output of SHOW SLAVE HOSTS on the master server for slaves started with the --report-user and --report-password options.

  • --slave-checkpoint-group=#

    Command-Line Format--slave-checkpoint-group=#
    Permitted ValuesTypeinteger
    Default512
    Min Value32
    Max Value524280
    Block Size8

    Sets the maximum number of transactions that can be processed by a multi-threaded slave before a checkpoint operation is called to update its status as shown by SHOW SLAVE STATUS. Setting this option has no effect on slaves for which multi-threading is not enabled.

    Note

    Multi-threaded slaves are not currently supported by MySQL Cluster, which silently ignores the setting for this option. See Section 20.6.3, “Known Issues in NDB Cluster Replication”, for more information.

    This option works in combination with the --slave-checkpoint-period option in such a way that, when either limit is exceeded, the checkpoint is executed and the counters tracking both the number of transactions and the time elapsed since the last checkpoint are reset.

    The minimum allowed value for this option is 32, unless the server was built using -DWITH_DEBUG, in which case the minimum value is 1. The effective value is always a multiple of 8; you can set it to a value that is not such a multiple, but the server rounds it down to the next lower multiple of 8 before storing the value. (Exception: No such rounding is performed by the debug server.) Regardless of how the server was built, the default value is 512, and the maximum allowed value is 524280.

  • --slave-checkpoint-period=#

    Command-Line Format--slave-checkpoint-period=#
    Permitted ValuesTypeinteger
    Default300
    Min Value1
    Max Value4G

    Sets the maximum time (in milliseconds) that is allowed to pass before a checkpoint operation is called to update the status of a multi-threaded slave as shown by SHOW SLAVE STATUS. Setting this option has no effect on slaves for which multi-threading is not enabled.

    Note

    Multi-threaded slaves are not currently supported by MySQL Cluster, which silently ignores the setting for this option. See Section 20.6.3, “Known Issues in NDB Cluster Replication”, for more information.

    This option works in combination with the --slave-checkpoint-group option in such a way that, when either limit is exceeded, the checkpoint is executed and the counters tracking both the number of transactions and the time elapsed since the last checkpoint are reset.

    The minimum allowed value for this option is 1, unless the server was built using -DWITH_DEBUG, in which case the minimum value is 0. Regardless of how the server was built, the default value is 300, and the maximum possible value is 4294967296 (4GB).

  • --slave-parallel-workers

    Command-Line Format--slave-parallel-workers=#
    Permitted ValuesTypeinteger
    Default0
    Min Value0
    Max Value1024

    Sets the number of slave applier threads for executing replication transactions in parallel. Setting this variable to a number greater than 0 creates a multi-threaded slave with this number of applier threads. When set to 0 (the default) parallel execution is disabled and the slave uses a single applier thread.

    A multi-threaded slave provides parallel execution by using a coordinator thread and the number of applier threads configured by this option. The way which transactions are distributed among applier threads is configured by --slave-parallel-type. For more information about multi-threaded slaves see slave-parallel-workers.

    Note

    Multi-threaded slaves are not currently supported by MySQL Cluster, which silently ignores the setting for this option. See Section 20.6.3, “Known Issues in NDB Cluster Replication”, for more information.

  • --slave-pending-jobs-size-max=#

    Command-Line Format--slave-pending-jobs-size-max=#
    Permitted ValuesTypeinteger
    Default16M
    Min Value1024
    Max Value18EB
    Block Size1024

    For multi-threaded slaves, this option sets the maximum amount of memory (in bytes) available to slave worker queues holding events not yet applied. Setting this option has no effect on slaves for which multi-threading is not enabled.

    The minimum possible value for this option is 1024; the default is 16MB. The maximum possible value is 18446744073709551615 (16 exabytes). Values that are not exact multiples of 1024 are rounded down to the next-highest multiple of 1024 prior to being stored.

    Important

    The value for this option must not be less than the master's value for max_allowed_packet; otherwise a slave worker queue may become full while there remain events coming from the master to be processed.

  • --skip-slave-start

    Command-Line Format--skip-slave-start
    Permitted ValuesTypeboolean
    DefaultFALSE

    Tells the slave server not to start the slave threads when the server starts. To start the threads later, use a START SLAVE statement.

  • --slave_compressed_protocol={0|1}

    Command-Line Format--slave_compressed_protocol
    System VariableNameslave_compressed_protocol
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    If this option is set to 1, use compression for the slave/master protocol if both the slave and the master support it. The default is 0 (no compression).

  • --slave-load-tmpdir=dir_name

    Command-Line Format--slave-load-tmpdir=dir_name
    System VariableNameslave_load_tmpdir
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypedirectory name
    Default/tmp

    The name of the directory where the slave creates temporary files. This option is by default equal to the value of the tmpdir system variable. When the slave SQL thread replicates a LOAD DATA INFILE statement, it extracts the file to be loaded from the relay log into temporary files, and then loads these into the table. If the file loaded on the master is huge, the temporary files on the slave are huge, too. Therefore, it might be advisable to use this option to tell the slave to put temporary files in a directory located in some file system that has a lot of available space. In that case, the relay logs are huge as well, so you might also want to use the --relay-log option to place the relay logs in that file system.

    The directory specified by this option should be located in a disk-based file system (not a memory-based file system) because the temporary files used to replicate LOAD DATA INFILE must survive machine restarts. The directory also should not be one that is cleared by the operating system during the system startup process.

  • slave-max-allowed-packet=bytes

    Command-Line Format--slave-max-allowed-packet=#
    Permitted ValuesTypeinteger
    Default1073741824
    Min Value1024
    Max Value1073741824

    This option sets the maximum packet size in bytes for the slave SQL and I/O threads, so that large updates using row-based replication do not cause replication to fail because an update exceeded max_allowed_packet. (Bug #12400221, Bug #60926)

    The corresponding server variable slave_max_allowed_packet always has a value that is a positive integer multiple of 1024; if you set it to some value that is not such a multiple, the value is automatically rounded down to the next highest multiple of 1024. (For example, if you start the server with --slave-max-allowed-packet=10000, the value used is 9216; setting 0 as the value causes 1024 to be used.) A truncation warning is issued in such cases.

    The maximum (and default) value is 1073741824 (1 GB); the minimum is 1024.

  • --slave-net-timeout=seconds

    Command-Line Format--slave-net-timeout=#
    System VariableNameslave_net_timeout
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default3600
    Min Value1
    Permitted Values (>= 5.7.7)Typeinteger
    Default60
    Min Value1

    The number of seconds to wait for more data from the master before the slave considers the connection broken, aborts the read, and tries to reconnect. The first retry occurs immediately after the timeout. The interval between retries is controlled by the MASTER_CONNECT_RETRY option for the CHANGE MASTER TO statement, and the number of reconnection attempts is limited by the --master-retry-count option. Prior to MySQL 5.7.7, the default was 3600 seconds (one hour). In MySQL 5.7.7 and later the default is 60 (one minute).

  • --slave-parallel-type=type

    Introduced5.7.2
    Command-Line Format--slave-parallel-type=type
    Permitted ValuesTypeenumeration
    DefaultDATABASE
    Valid ValuesDATABASE
    LOGICAL_CLOCK

    When using a multi-threaded slave (slave_parallel_workers is greater than 0), this option specifies the policy used to decide which transactions are allowed to execute in parallel on the slave. The possible values are:

    • DATABASE: Transactions that update different databases are applied in parallel. This value is only appropriate if data is partitioned into multiple databases which are being updated independently and concurrently on the master. Only recommended if there are no cross-database constraints, as such constraints may be violated on the slave.

    • LOGICAL_CLOCK: Transactions that are part of the same binary log group commit on a master are applied in parallel on a slave. There are no cross-database constraints, and data does not need to be partitioned into multiple databases.

    Regardless of the value of this variable, there is no special configuration required on the master. When slave_preserve_commit_order=1, you can only use LOGICAL_CLOCK. If your replication topology uses multiple levels of slaves, LOGICAL_CLOCK may achieve less parallelization for each level the slave is away from the master.

  • slave-rows-search-algorithms=list

    Command-Line Format--slave-rows-search-algorithms=list
    Permitted ValuesTypeset
    DefaultTABLE_SCAN,INDEX_SCAN
    Valid ValuesTABLE_SCAN,INDEX_SCAN
    INDEX_SCAN,HASH_SCAN
    TABLE_SCAN,HASH_SCAN
    TABLE_SCAN,INDEX_SCAN,HASH_SCAN (equivalent to INDEX_SCAN,HASH_SCAN)

    When preparing batches of rows for row-based logging and replication, this option controls how the rows are searched for matches—that is, whether or not hashing is used for searches using a primary or unique key, some other key, or no key at all. This option takes a comma-separated list of any 2 (or possibly 3) values from the list INDEX_SCAN, TABLE_SCAN, HASH_SCAN. The list need not be quoted, but must contain no spaces, whether or not quotes are used. Possible combinations (lists) and their effects are shown in the following table:

    Index used / option valueINDEX_SCAN,HASH_SCAN or INDEX_SCAN,TABLE_SCAN,HASH_SCANINDEX_SCAN,TABLE_SCANTABLE_SCAN,HASH_SCAN
    Primary key or unique keyIndex scanIndex scanHash scan over index
    (Other) KeyHash scan over indexIndex scanHash scan over index
    No indexHash scanTable scanHash scan

    The order in which the algorithms are specified in the list does not make any difference in the order in which they are displayed by a SELECT or SHOW VARIABLES statement (which is the same as that used in the table just shown previously).The default value is TABLE_SCAN,INDEX_SCAN, which means that all searches that can use indexes do use them, and searches without any indexes use table scans.

    Specifying INDEX_SCAN,TABLE_SCAN,HASH_SCAN has the same effect as specifying INDEX_SCAN,HASH_SCAN. To use hashing for any searches that does not use a primary or unique key, set this option to INDEX_SCAN,HASH_SCAN. To force hashing for all searches, set it to TABLE_SCAN,HASH_SCAN.

    Note

    There is only a performance advantage for INDEX_SCAN and HASH_SCAN if the row events are big enough. The size of row events is configured using --binlog-row-event-max-size. For example, suppose a DELETE statement which deletes 25,000 rows generates large Delete_row_event events. In this case if slave_rows_search_algorithms is set to INDEX_SCAN or HASH_SCAN there is a performance improvement. However, if there are 25,000 DELETE statements and each is represented by a separate event then setting slave_rows_search_algorithms to INDEX_SCAN or HASH_SCAN provides no performance improvement while executing these separate events.

  • --slave-skip-errors=[err_code1,err_code2,...|all|ddl_exist_errors]

    Command-Line Format--slave-skip-errors=name
    System VariableNameslave_skip_errors
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring
    DefaultOFF
    Valid ValuesOFF
    [list of error codes]
    all
    ddl_exist_errors
    Permitted ValuesTypestring
    DefaultOFF
    Valid ValuesOFF
    [list of error codes]
    all
    ddl_exist_errors
    Permitted ValuesTypestring
    DefaultOFF
    Valid ValuesOFF
    [list of error codes]
    all
    ddl_exist_errors

    Normally, replication stops when an error occurs on the slave, which gives you the opportunity to resolve the inconsistency in the data manually. This option causes the slave SQL thread to continue replication when a statement returns any of the errors listed in the option value.

    Do not use this option unless you fully understand why you are getting errors. If there are no bugs in your replication setup and client programs, and no bugs in MySQL itself, an error that stops replication should never occur. Indiscriminate use of this option results in slaves becoming hopelessly out of synchrony with the master, with you having no idea why this has occurred.

    For error codes, you should use the numbers provided by the error message in your slave error log and in the output of SHOW SLAVE STATUS. Appendix B, Errors, Error Codes, and Common Problems, lists server error codes.

    You can also (but should not) use the very nonrecommended value of all to cause the slave to ignore all error messages and keeps going regardless of what happens. Needless to say, if you use all, there are no guarantees regarding the integrity of your data. Please do not complain (or file bug reports) in this case if the slave's data is not anywhere close to what it is on the master. You have been warned.

    MySQL 5.7 supports an additional shorthand value ddl_exist_errors, which is equivalent to the error code list 1007,1008,1050,1051,1054,1060,1061,1068,1094,1146.

    Examples:

    --slave-skip-errors=1062,1053
    --slave-skip-errors=all
    --slave-skip-errors=ddl_exist_errors
    
  • --slave-sql-verify-checksum={0|1}

    Command-Line Format--slave-sql-verify-checksum=value
    Permitted ValuesTypeboolean
    Default0
    Valid Values0
    1

    When this option is enabled, the slave examines checksums read from the relay log, in the event of a mismatch, the slave stops with an error. Disabled by default.

The following options are used internally by the MySQL test suite for replication testing and debugging. They are not intended for use in a production setting.

  • --abort-slave-event-count

    Command-Line Format--abort-slave-event-count=#
    Permitted ValuesTypeinteger
    Default0
    Min Value0

    When this option is set to some positive integer value other than 0 (the default) it affects replication behavior as follows: After the slave SQL thread has started, value log events are permitted to be executed; after that, the slave SQL thread does not receive any more events, just as if the network connection from the master were cut. The slave thread continues to run, and the output from SHOW SLAVE STATUS displays Yes in both the Slave_IO_Running and the Slave_SQL_Running columns, but no further events are read from the relay log.

  • --disconnect-slave-event-count

    Command-Line Format--disconnect-slave-event-count=#
    Permitted ValuesTypeinteger
    Default0
Options for Logging Slave Status to Tables

MySQL 5.7 supports logging of replication slave status information to tables rather than files. Writing of the master info log and the relay log info log can be configured separately using the two server options listed here:

  • --master-info-repository={FILE|TABLE}

    Command-Line Format--master-info-repository=FILE|TABLE
    Permitted ValuesTypestring
    DefaultFILE
    Valid ValuesFILE
    TABLE

    This option causes the server to write its master info log to a file or a table. The name of the file defaults to master.info; you can change the name of the file using the --master-info-file server option.

    The default value for this option is FILE. If you use TABLE, the log is written to the slave_master_info table in the mysql database.

  • --relay-log-info-repository={FILE|TABLE}

    Command-Line Format--relay-log-info-repository=FILE|TABLE
    Permitted ValuesTypestring
    DefaultFILE
    Valid ValuesFILE
    TABLE

    This option causes the server to log its relay log info to a file or a table. The name of the file defaults to relay-log.info; you can change the name of the file using the --relay-log-info-file server option.

    The default value for this option is FILE. If you use TABLE, the log is written to the slave_relay_log_info table in the mysql database.

These options can be used to make replication slaves resilient to unexpected halts. See Section 18.3.2, “Handling an Unexpected Halt of a Replication Slave”, for more information.

The info log tables and their contents are considered local to a given MySQL Server. They are not replicated, and changes to them are not written to the binary log.

For more information, see Section 18.2.4, “Replication Relay and Status Logs”.

System Variables Used on Replication Slaves

The following list describes system variables for controlling replication slave servers. They can be set at server startup and some of them can be changed at runtime using SET. Server options used with replication slaves are listed earlier in this section.

  • init_slave

    Command-Line Format--init-slave=name
    System VariableNameinit_slave
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypestring

    This variable is similar to init_connect, but is a string to be executed by a slave server each time the SQL thread starts. The format of the string is the same as for the init_connect variable. The setting of this variable takes effect for subsequent START SLAVE statements.

    Note

    The SQL thread sends an acknowledgment to the client before it executes init_slave. Therefore, it is not guaranteed that init_slave has been executed when START SLAVE returns. See Section 14.4.2.6, “START SLAVE Syntax”, for more information.

  • log_slow_slave_statements

    Introduced5.7.1
    System VariableNamelog_slow_slave_statements
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    When the slow query log is enabled, this variable enables logging for queries that have taken more than long_query_time seconds to execute on the slave. This variable was added in MySQL 5.7.1. Setting this variable has no immediate effect. The state of the variable applies on all subsequent START SLAVE statements.

  • master_info_repository

    Command-Line Format--master-info-repository=FILE|TABLE
    System VariableNamemaster_info_repository
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypestring
    DefaultFILE
    Valid ValuesFILE
    TABLE

    The setting of this variable determines whether the slave logs master status and connection information to a FILE (master.info), or to a TABLE (mysql.slave_master_info). You can only change the value of this variable when no replication threads are executing.

    The setting of this variable also has a direct influence on the effect had by the setting of the sync_master_info system variable; see that variable's description for further information.

    This variable must be set to TABLE before configuring multiple replication channels. If you are using multiple replication channels then you cannot set this variable back to FILE.

  • relay_log

    Command-Line Format--relay-log=file_name
    System VariableNamerelay_log
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypefile name

    The base name of the relay log file, with no paths and no file extension. By default relay-log. The file name of individual files for the default replication channel is relay-log.XXXXXX, and for additional replication channels is relay-log-channel.XXXXXX.

  • relay_log_basename

    System VariableNamerelay_log_basename
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypefile name
    Defaultdatadir + '/' + hostname + '-relay-bin'

    Holds the name and complete path to the relay log file.

  • relay_log_index

    Command-Line Format--relay-log-index
    System VariableNamerelay_log_index
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypefile name
    Default*host_name*-relay-bin.index

    The name of the relay log index file for the default replication channel. The default name is host_name-relay-bin.index in the data directory, where host_name is the name of the slave server.

  • relay_log_info_file

    Command-Line Format--relay-log-info-file=file_name
    System VariableNamerelay_log_info_file
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypefile name
    Defaultrelay-log.info

    The name of the file in which the slave records information about the relay logs, when relay_log_info_repository=FILE. If relay_log_info_repository=TABLE, it is the file name that would be used in case the repository was changed to FILE). The default name is relay-log.info in the data directory.

  • relay_log_info_repository

    System VariableNamerelay_log_info_repository
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypestring
    DefaultFILE
    Valid ValuesFILE
    TABLE

    This variable determines whether the slave's position in the relay logs is written to a FILE (relay-log.info) or to a TABLE (mysql.slave_relay_log_info). You can only change the value of this variable when no replication threads are executing.

    The setting of this variable also has a direct influence on the effect had by the setting of the sync_relay_log_info system variable; see that variable's description for further information.

    This variable must be set to TABLE before configuring multiple replication channels. If you are using multiple replication channels then you cannot set this variable back to FILE.

  • relay_log_recovery

    Command-Line Format--relay-log-recovery
    System VariableNamerelay_log_recovery
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeboolean
    DefaultFALSE

    Enables automatic relay log recovery immediately following server startup. The recovery process creates a new relay log file, initializes the SQL thread position to this new relay log, and initializes the I/O thread to the SQL thread position. Reading of the relay log from the master then continues. In MySQL 5.7, this global variable is read-only; its value can be changed by starting the slave with the --relay-log-recovery option, which should be used following an unexpected halt of a replication slave to ensure that no possibly corrupted relay logs are processed. See Section 18.3.2, “Handling an Unexpected Halt of a Replication Slave” for more information.

    This variable also interacts with relay-log-purge, which controls purging of logs when they are no longer needed. Enabling the --relay-log-recovery option when relay-log-purge is disabled risks reading the relay log from files that were not purged, leading to data inconsistency.

    When relay_log_recovery is enabled and the slave has stopped due to errors encountered while running in multi-threaded mode, you can use START SLAVE UNTIL SQL_AFTER_MTS_GAPS to ensure that all gaps are processed before switching back to single-threaded mode or executing a CHANGE MASTER TO statement.

  • rpl_stop_slave_timeout

    Introduced5.7.2
    Command-Line Format--rpl-stop-slave-timeout=seconds
    System VariableNamerpl_stop_slave_timeout
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default31536000
    Min Value2
    Max Value31536000

    In MySQL 5.7.2 and later, you can control the length of time (in seconds) that STOP SLAVE waits before timing out by setting this variable. This can be used to avoid deadlocks between STOP SLAVE and other slave SQL statements using different client connections to the slave. The maximum and default value of rpl_stop_slave_timeout is 31536000 seconds (1 year). The minimum is 2 seconds. Changes to this variable take effect for subsequent STOP SLAVE statements. This variable affects only the client that issues a STOP SLAVE statement. When the timeout is reached, the issuing client stops waiting for the slave threads to stop, but the slave threads continue to try to stop.

  • slave_checkpoint_group

    Command-Line Format--slave-checkpoint-group=#
    System VariableNameslave_checkpoint_group=#
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default512
    Min Value32
    Max Value524280
    Block Size8

    Sets the maximum number of transactions that can be processed by a multi-threaded slave before a checkpoint operation is called to update its status as shown by SHOW SLAVE STATUS. Setting this variable has no effect on slaves for which multi-threading is not enabled. Setting this variable has no immediate effect. The state of the variable applies on all subsequent START SLAVE commands.

    Note

    Multi-threaded slaves are not currently supported by MySQL Cluster, which silently ignores the setting for this variable. See Section 20.6.3, “Known Issues in NDB Cluster Replication”, for more information.

    This variable works in combination with the slave_checkpoint_period system variable in such a way that, when either limit is exceeded, the checkpoint is executed and the counters tracking both the number of transactions and the time elapsed since the last checkpoint are reset.

    The minimum allowed value for this variable is 32, unless the server was built using -DWITH_DEBUG, in which case the minimum value is 1. The effective value is always a multiple of 8; you can set it to a value that is not such a multiple, but the server rounds it down to the next lower multiple of 8 before storing the value. (Exception: No such rounding is performed by the debug server.) Regardless of how the server was built, the default value is 512, and the maximum allowed value is 524280.

  • slave_checkpoint_period

    Command-Line Format--slave-checkpoint-period=#
    System VariableNameslave_checkpoint_period=#
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default300
    Min Value1
    Max Value4G

    Sets the maximum time (in milliseconds) that is allowed to pass before a checkpoint operation is called to update the status of a multi-threaded slave as shown by SHOW SLAVE STATUS. Setting this variable has no effect on slaves for which multi-threading is not enabled. Setting this variable takes effect for all replication channels immediately, including running channels.

    Note

    Multi-threaded slaves are not currently supported by MySQL Cluster, which silently ignores the setting for this variable. See Section 20.6.3, “Known Issues in NDB Cluster Replication”, for more information.

    This variable works in combination with the slave_checkpoint_group system variable in such a way that, when either limit is exceeded, the checkpoint is executed and the counters tracking both the number of transactions and the time elapsed since the last checkpoint are reset.

    The minimum allowed value for this variable is 1, unless the server was built using -DWITH_DEBUG, in which case the minimum value is 0. Regardless of how the server was built, the default value is 300, and the maximum possible value is 4294967296 (4GB).

  • slave_compressed_protocol

    Command-Line Format--slave_compressed_protocol
    System VariableNameslave_compressed_protocol
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    Whether to use compression of the slave/master protocol if both the slave and the master support it. Changes to this variable take effect on subsequent connection attempts; this includes after issuing a START SLAVE statement, as well as reconnections made by a running I/O thread (for example after issuing a CHANGE MASTER TO MASTER_RETRY_COUNT statement).

  • slave_exec_mode

    Command-Line Format--slave-exec-mode=mode
    System VariableNameslave_exec_mode
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    DefaultSTRICT (ALL)
    DefaultIDEMPOTENT (NDB)
    Valid ValuesIDEMPOTENT
    STRICT

    Controls how a slave thread resolves conflicts and errors during replication. STRICT mode is the default, and is suitable for most cases. IDEMPOTENT mode causes suppression of duplicate-key and no-key-found errors. This mode should only be used with MySQL Cluster Replication in some special scenarios, such as multi-master replication, and circular replication. (See Section 20.6.10, “NDB Cluster Replication: Multi-Master and Circular Replication”, and Section 20.6.11, “NDB Cluster Replication Conflict Resolution”, for more information.) Setting this variable takes effect for all replication channels immediately, including running channels.

    Warning

    The mysqld supplied with MySQL Cluster ignores any value explicitly set for slave_exec_mode, and always treats it as IDEMPOTENT.

    IDEMPOTENT mode is supported only by NDB and is used when replicating NDB to InnoDB.

  • slave_load_tmpdir

    Command-Line Format--slave-load-tmpdir=dir_name
    System VariableNameslave_load_tmpdir
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypedirectory name
    Default/tmp

    The name of the directory where the slave creates temporary files for replicating LOAD DATA INFILE statements. Setting this variable takes effect for all replication channels immediately, including running channels.

  • slave_max_allowed_packet

    System VariableNameslave_max_allowed_packet
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default1073741824
    Min Value1024
    Max Value1073741824

    This variable sets the maximum packet size for the slave SQL and I/O threads, so that large updates using row-based replication do not cause replication to fail because an update exceeded max_allowed_packet. Setting this variable takes effect for all replication channels immediately, including running channels.

    This global variable always has a value that is a positive integer multiple of 1024; if you set it to some value that is not, the value is rounded down to the next highest multiple of 1024 for it is stored or used; setting slave_max_allowed_packet to 0 causes 1024 to be used. (A truncation warning is issued in all such cases.) The default and maximum value is 1073741824 (1 GB); the minimum is 1024.

    slave_max_allowed_packet can also be set at startup, using the --slave-max-allowed-packet option.

  • slave_net_timeout

    Command-Line Format--slave-net-timeout=#
    System VariableNameslave_net_timeout
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default3600
    Min Value1
    Permitted Values (>= 5.7.7)Typeinteger
    Default60
    Min Value1

    The number of seconds to wait for more data from a master/slave connection before aborting the read. Setting this variable has no immediate effect. The state of the variable applies on all subsequent START SLAVE commands.

  • slave_parallel_type=type

    Introduced5.7.2
    Command-Line Format--slave-parallel-type=type
    Permitted ValuesTypeenumeration
    DefaultDATABASE
    Valid ValuesDATABASE
    LOGICAL_CLOCK

    When using a multi-threaded slave (slave_parallel_workers is greater than 0), this variable specifies the policy used to decide which transactions are allowed to execute in parallel on the slave. See --slave-parallel-type for more information.

  • slave_parallel_workers

    Command-Line Format--slave-parallel-workers=#
    System VariableNameslave_parallel_workers
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0
    Min Value0
    Max Value1024

    Sets the number of slave applier threads for executing replication transactions in parallel. Setting this variable to a number greater than 0 creates a multi-threaded slave with this number of applier threads. When set to 0 (the default) parallel execution is disabled and the slave uses a single applier thread. Setting slave_parallel_workers has no immediate effect. The state of the variable applies on all subsequent START SLAVE statements.

    Note

    Multi-threaded slaves are not currently supported by MySQL Cluster, which silently ignores the setting for this variable. See Section 20.6.3, “Known Issues in NDB Cluster Replication”, for more information.

    A multi-threaded slave provides parallel execution by using a coordinator thread and the number of applier threads configured by this variable. The way which transactions are distributed among applier threads is configured by slave_parallel_type. The transactions that the slave applies in parallel may commit out of order, unless slave_preserve_commit_order=1. Therefore, checking for the most recently executed transaction does not guarantee that all previous transactions from the master have been executed on the slave. This has implications for logging and recovery when using a multi-threaded slave. For example, on a multi-threaded slave the START SLAVE UNTIL statement only supports using SQL_AFTER_MTS_GAPS.

    In MySQL 5.7.5 and later, retrying of transactions is supported when multi-threading is enabled on a slave. In previous versions, slave_transaction_retries was treated as equal to 0 when using multi-threaded slaves.

  • slave_pending_jobs_size_max

    System VariableNameslave_pending_jobs_size_max
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default16M
    Min Value1024
    Max Value18EB
    Block Size1024

    For multi-threaded slaves, this variable sets the maximum amount of memory (in bytes) available to slave worker queues holding events not yet applied. Setting this variable has no effect on slaves for which multi-threading is not enabled. Setting this variable has no immediate effect. The state of the variable applies on all subsequent START SLAVE commands.

    The minimum possible value for this variable is 1024; the default is 16MB. The maximum possible value is 18446744073709551615 (16 exabytes). Values that are not exact multiples of 1024 are rounded down to the next-highest multiple of 1024 prior to being stored.

    Important

    The value of this variable must not be less than the master's value for max_allowed_packet; otherwise a slave worker queue may become full while there remain events coming from the master to be processed.

  • slave_preserve_commit_order

    Introduced5.7.5
    Command-Line Format--slave-preserve-commit-order=value
    System VariableNameslave_preserve_commit_order
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    Default0
    Valid Values0
    1

    For multi-threaded slaves, enabling this variable ensures that transactions are externalized on the slave in the same order as they appear in the slave's relay log. Setting this variable has no effect on slaves for which multi-threading is not enabled. All replication threads (for all replication channels if you are using multiple replication channels) must be stopped before changing this variable. --log-bin and --log-slave-updates must be enabled on the slave. In addition --slave-parallel-type must be set to LOGICAL_CLOCK.

    Once a multi-threaded slave has been started, transactions can begin to execute in parallel. With slave_preserve_commit_order enabled, the executing thread waits until all previous transactions are committed before committing. While the slave thread is waiting for other workers to commit their transactions it reports its status as Waiting for preceding transaction to commit. (Prior to MySQL 5.7.8, this was shown as Waiting for its turn to commit.) Enabling this mode on a multi-threaded slave ensures that it never enters a state that the master was not in. This makes it well suited to using replication for read scale-out. See Section 18.3.4, “Using Replication for Scale-Out”.

    When using a multi-threaded slave, if slave_preserve_commit_order is not enabled, there is a chance of gaps in the sequence of transactions that have been executed from the slave's relay log. When this option is enabled, there is not this chance of gaps, but Exec_master_log_pos may be behind the position up to which has been executed. See Section 18.4.1.34, “Replication and Transaction Inconsistencies” for more information.

  • slave_rows_search_algorithms

    System VariableNameslave_rows_search_algorithms=list
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeset
    DefaultTABLE_SCAN,INDEX_SCAN
    Valid ValuesTABLE_SCAN,INDEX_SCAN
    INDEX_SCAN,HASH_SCAN
    TABLE_SCAN,HASH_SCAN
    TABLE_SCAN,INDEX_SCAN,HASH_SCAN (equivalent to INDEX_SCAN,HASH_SCAN)

    When preparing batches of rows for row-based logging and replication, this variable controls how the rows are searched for matches—that is, whether or not hashing is used for searches using a primary or unique key, using some other key, or using no key at all. Setting this variable takes effect for all replication channels immediately, including running channels.

    This variable takes a comma-separated list of at least 2 values from the list INDEX_SCAN, TABLE_SCAN, HASH_SCAN. The value expected as a string, so the value must be quoted. In addition, the value must not contain any spaces. Possible combinations (lists) and their effects are shown in the following table:

    Index used / option valueINDEX_SCAN,HASH_SCAN or INDEX_SCAN,TABLE_SCAN,HASH_SCANINDEX_SCAN,TABLE_SCANTABLE_SCAN,HASH_SCAN
    Primary key or unique keyIndex scanindex scanIndex hash
    (Other) KeyIndex hashIndex scanIndex hash
    No indexTable hashTable scanTable hash

    The order in which the algorithms are specified in the list does not make any difference in the order in which they are displayed by a SELECT or SHOW VARIABLES statement, as shown here:

    mysql> SET GLOBAL slave_rows_search_algorithms = "INDEX_SCAN,TABLE_SCAN";
    Query OK, 0 rows affected (0.00 sec)
    
    mysql> SHOW VARIABLES LIKE '%algorithms%';
    +------------------------------+-----------------------+
    | Variable_name                | Value                 |
    +------------------------------+-----------------------+
    | slave_rows_search_algorithms | TABLE_SCAN,INDEX_SCAN |
    +------------------------------+-----------------------+
    1 row in set (0.00 sec)
    
    mysql> SET GLOBAL slave_rows_search_algorithms = "TABLE_SCAN,INDEX_SCAN";
    Query OK, 0 rows affected (0.00 sec)
    
    mysql> SHOW VARIABLES LIKE '%algorithms%';
    +------------------------------+-----------------------+
    | Variable_name                | Value                 |
    +------------------------------+-----------------------+
    | slave_rows_search_algorithms | TABLE_SCAN,INDEX_SCAN |
    +------------------------------+-----------------------+
    1 row in set (0.00 sec)
    

    The default value is TABLE_SCAN,INDEX_SCAN, which means that all searches that can use indexes do use them, and searches without any indexes use table scans.

    Specifying INDEX_SCAN,TABLE_SCAN,HASH_SCAN has the same effect as specifying INDEX_SCAN,HASH_SCAN. To use hashing for any searches that does not use a primary or unique key, set this variable to INDEX_SCAN,HASH_SCAN. To force hashing for all searches, set it to TABLE_SCAN,HASH_SCAN.

  • slave_skip_errors

    Command-Line Format--slave-skip-errors=name
    System VariableNameslave_skip_errors
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring
    DefaultOFF
    Valid ValuesOFF
    [list of error codes]
    all
    ddl_exist_errors
    Permitted ValuesTypestring
    DefaultOFF
    Valid ValuesOFF
    [list of error codes]
    all
    ddl_exist_errors
    Permitted ValuesTypestring
    DefaultOFF
    Valid ValuesOFF
    [list of error codes]
    all
    ddl_exist_errors

    Normally, replication stops when an error occurs on the slave, which gives you the opportunity to resolve the inconsistency in the data manually. This variable causes the slave SQL thread to continue replication when a statement returns any of the errors listed in the variable value. The setting of this variable takes effect immediately, even for running replication threads.

  • slave_sql_verify_checksum

    System VariableNameslave_sql_verify_checksum
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    Default1
    Valid Values0
    1

    Cause the slave SQL thread to verify data using the checksums read from the relay log. In the event of a mismatch, the slave stops with an error. Setting this variable takes effect for all replication channels immediately, including running channels.

    Note

    The slave I/O thread always reads checksums if possible when accepting events from over the network.

  • slave_transaction_retries

    Command-Line Format--slave_transaction_retries=#
    System VariableNameslave_transaction_retries
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default10
    Min Value0
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default10
    Min Value0
    Max Value18446744073709551615

    If a replication slave SQL thread fails to execute a transaction because of an InnoDB deadlock or because the transaction's execution time exceeded InnoDB's innodb_lock_wait_timeout or NDB's TransactionDeadlockDetectionTimeout or TransactionInactiveTimeout, it automatically retries slave_transaction_retries times before stopping with an error. The default value is 10. Setting this variable takes effect for all replication channels immediately, including running channels.

    As of MySQL 5.7.5, retrying of transactions is supported when multi-threading is enabled on a slave. In previous versions, slave_transaction_retries was treated as equal to 0 when using multi-threaded slaves.

  • slave_type_conversions

    Command-Line Format--slave_type_conversions=set
    System VariableNameslave_type_conversions
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted Values (<= 5.7.1)Typeset
    Default
    Valid ValuesALL_LOSSY
    ALL_NON_LOSSY
    Permitted Values (>= 5.7.2)Typeset
    Default
    Valid ValuesALL_LOSSY
    ALL_NON_LOSSY
    ALL_SIGNED
    ALL_UNSIGNED

    Controls the type conversion mode in effect on the slave when using row-based replication. In MySQL 5.7.2 and later, its value is a comma-delimited set of zero or more elements from the list: ALL_LOSSY, ALL_NON_LOSSY, ALL_SIGNED, ALL_UNSIGNED. Set this variable to an empty string to disallow type conversions between the master and the slave. Setting this variable takes effect for all replication channels immediately, including running channels.

    ALL_SIGNED and ALL_UNSIGNED were added in MySQL 5.7.2 (Bug#15831300). For additional information on type conversion modes applicable to attribute promotion and demotion in row-based replication, see Row-based replication: attribute promotion and demotion.

  • sql_slave_skip_counter

    System VariableNamesql_slave_skip_counter
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger

    The number of events from the master that a slave server should skip. Setting the option has no immediate effect. The variable applies to the next START SLAVE statement; the next START SLAVE statement also changes the value back to 0. When this variable is set to a non-zero value and there are multiple replication channels configured, the START SLAVE statement can only be used with the FOR CHANNEL channel clause.

    This option is incompatible with GTID-based replication, and must not be set to a nonzero value when --gtid-mode=ON. In MySQL 5.7.1 and later, trying to do so is specifically disallowed. (Bug #15833516) If you need to skip transactions when employing GTIDs, use gtid_executed from the master instead. See Injecting empty transactions, for information about how to do this.

    Important

    If skipping the number of events specified by setting this variable would cause the slave to begin in the middle of an event group, the slave continues to skip until it finds the beginning of the next event group and begins from that point. For more information, see Section 14.4.2.5, “SET GLOBAL sql_slave_skip_counter Syntax”.

  • sync_master_info

    Command-Line Format--sync-master-info=#
    System VariableNamesync_master_info
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default10000
    Min Value0
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default10000
    Min Value0
    Max Value18446744073709551615

    The effects of this variable on a replication slave depend on whether the slave's master_info_repository is set to FILE or TABLE, as explained in the following paragraphs.

    master_info_repository = FILE.  If the value of sync_master_info is greater than 0, the slave synchronizes its master.info file to disk (using fdatasync()) after every sync_master_info events. If it is 0, the MySQL server performs no synchronization of the master.info file to disk; instead, the server relies on the operating system to flush its contents periodically as with any other file.

    master_info_repository = TABLE.  If the value of sync_master_info is greater than 0, the slave updates its master info repository table after every sync_master_info events. If it is 0, the table is never updated.

    The default value for sync_master_info is 10000. Setting this variable takes effect for all replication channels immediately, including running channels.

  • sync_relay_log

    Command-Line Format--sync-relay-log=#
    System VariableNamesync_relay_log
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default10000
    Min Value0
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default10000
    Min Value0
    Max Value18446744073709551615

    If the value of this variable is greater than 0, the MySQL server synchronizes its relay log to disk (using fdatasync()) after every sync_relay_log events are written to the relay log. Setting this variable takes effect for all replication channels immediately, including running channels.

    Setting sync_relay_log to 0 causes no synchronization to be done to disk; in this case, the server relies on the operating system to flush the relay log's contents from time to time as for any other file.

    A value of 1 is the safest choice because in the event of a crash you lose at most one event from the relay log. However, it is also the slowest choice (unless the disk has a battery-backed cache, which makes synchronization very fast).

  • sync_relay_log_info

    Command-Line Format--sync-relay-log-info=#
    System VariableNamesync_relay_log_info
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default10000
    Min Value0
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default10000
    Min Value0
    Max Value18446744073709551615

    The effects of this variable on the slave depend on the server's relay_log_info_repository setting (FILE or TABLE), and if this is TABLE, additionally on whether the storage engine used by the relay log info table is transactional (such as InnoDB) or not (MyISAM). The effects of these factors on the behavior of the server for sync_relay_log_info values of zero and greater than zero are shown in the following table:

    sync_relay_log_inforelay_log_info_repository
    FILETABLE
    TransactionalNontransactional
    N > 0

    The slave synchronizes its relay-log.info file to disk (using fdatasync()) after every N transactions.

    The table is updated after each transaction. (N is effectively ignored.)

    The table is updated after every N events.

    0

    The MySQL server performs no synchronization of the relay-log.info file to disk; instead, the server relies on the operating system to flush its contents periodically as with any other file.

    The table is never updated.

    The default value for sync_relay_log_info is 10000. Setting this variable takes effect for all replication channels immediately, including running channels.

18.1.6.4 Binary Logging Options and Variables

Startup Options Used with Binary Logging

System Variables Used with Binary Logging

You can use the mysqld options and system variables that are described in this section to affect the operation of the binary log as well as to control which statements are written to the binary log. For additional information about the binary log, see Section 6.4.4, “The Binary Log”. For additional information about using MySQL server options and system variables, see Section 6.1.4, “Server Command Options”, and Section 6.1.5, “Server System Variables”.

Startup Options Used with Binary Logging

The following list describes startup options for enabling and configuring the binary log. System variables used with binary logging are discussed later in this section.

  • --binlog-row-event-max-size=N

    Command-Line Format--binlog-row-event-max-size=#
    Permitted Values (32-bit platforms)Typeinteger
    Default8192
    Min Value256
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default8192
    Min Value256
    Max Value18446744073709551615

    Specify the maximum size of a row-based binary log event, in bytes. Rows are grouped into events smaller than this size if possible. The value should be a multiple of 256. The default is 8192. See Section 18.2.1, “Replication Formats”.

  • --log-bin[=base_name]

    Command-Line Format--log-bin
    System VariableNamelog_bin
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypefile name

    Enable binary logging. The server logs all statements that change data to the binary log, which is used for backup and replication. See Section 6.4.4, “The Binary Log”.

    The option value, if given, is the base name for the log sequence. The server creates binary log files in sequence by adding a numeric suffix to the base name. It is recommended that you specify a base name (see Section B.5.7, “Known Issues in MySQL”, for the reason). Otherwise, MySQL uses host_name-bin as the base name.

    When the server reads an entry from the index file, it checks whether the entry contains a relative path, and if it does, the relative part of the path in replaced with the absolute path set using the --log-bin option. An absolute path remains unchanged; in such a case, the index must be edited manually to enable the new path or paths to be used. (In older versions of MySQL, manual intervention was required whenever relocating the binary log or relay log files.) (Bug #11745230, Bug #12133)

    Setting this option causes the log_bin system variable to be set to ON (or 1), and not to the base name. The binary log file name (with path) is available as the log_bin_basename system variable.

    In MySQL 5.7.3 and later, if you specify this option without also specifying a --server-id, the server is not allowed to start. (Bug #11763963, Bug #56739)

  • --log-bin-index[=file_name]

    Command-Line Format--log-bin-index=file_name
    Permitted ValuesTypefile name

    The index file for binary log file names. See Section 6.4.4, “The Binary Log”. If you omit the file name, and if you did not specify one with --log-bin, MySQL uses host_name-bin.index as the file name.

  • --log-bin-trust-function-creators[={0|1}]

    Command-Line Format--log-bin-trust-function-creators
    System VariableNamelog_bin_trust_function_creators
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultFALSE

    This option sets the corresponding log_bin_trust_function_creators system variable. If no argument is given, the option sets the variable to 1. log_bin_trust_function_creators affects how MySQL enforces restrictions on stored function and trigger creation. See Section 22.7, “Binary Logging of Stored Programs”.

  • --log-bin-use-v1-row-events[={0|1}]

    Command-Line Format--log-bin-use-v1-row-events[={0|1}]
    System VariableNamelog_bin_use_v1_row_events
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeboolean
    Default0

    MySQL 5.7 uses Version 2 binary log row events, which cannot be read by MySQL Server releases prior to MySQL 5.6.6. Setting this option to 1 causes mysqld to write the binary log using Version 1 logging events, which is the only version of binary log events used in previous releases, and thus produce binary logs that can be read by older slaves. Setting --log-bin-use-v1-row-events to 0 (the default) causes mysqld to use Version 2 binary log events.

    The value used for this option can be obtained from the read-only log_bin_use_v1_row_events system variable.

    --log-bin-use-v1-row-events is chiefly of interest when setting up replication conflict detection and resolution using NDB$EPOCH_TRANS() as the conflict detection function, which requires Version 2 binary log row events. Thus, this option and --ndb-log-transaction-id are not compatible.

    For more information, see Section 20.6.11, “NDB Cluster Replication Conflict Resolution”.

Statement selection options.  The options in the following list affect which statements are written to the binary log, and thus sent by a replication master server to its slaves. There are also options for slave servers that control which statements received from the master should be executed or ignored. For details, see Section 18.1.6.3, “Replication Slave Options and Variables”.

  • --binlog-do-db=db_name

    Command-Line Format--binlog-do-db=name
    Permitted ValuesTypestring

    This option affects binary logging in a manner similar to the way that --replicate-do-db affects replication.

    The effects of this option depend on whether the statement-based or row-based logging format is in use, in the same way that the effects of --replicate-do-db depend on whether statement-based or row-based replication is in use. You should keep in mind that the format used to log a given statement may not necessarily be the same as that indicated by the value of binlog_format. For example, DDL statements such as CREATE TABLE and ALTER TABLE are always logged as statements, without regard to the logging format in effect, so the following statement-based rules for --binlog-do-db always apply in determining whether or not the statement is logged.

    Statement-based logging.  Only those statements are written to the binary log where the default database (that is, the one selected by USE) is db_name. To specify more than one database, use this option multiple times, once for each database; however, doing so does not cause cross-database statements such as UPDATE some_db.some_table SET foo='bar' to be logged while a different database (or no database) is selected.

    Warning

    To specify multiple databases you must use multiple instances of this option. Because database names can contain commas, the list will be treated as the name of a single database if you supply a comma-separated list.

    An example of what does not work as you might expect when using statement-based logging: If the server is started with --binlog-do-db=sales and you issue the following statements, the UPDATE statement is not logged:

    USE prices;
    UPDATE sales.january SET amount=amount+1000;
    

    The main reason for this just check the default database behavior is that it is difficult from the statement alone to know whether it should be replicated (for example, if you are using multiple-table DELETE statements or multiple-table UPDATE statements that act across multiple databases). It is also faster to check only the default database rather than all databases if there is no need.

    Another case which may not be self-evident occurs when a given database is replicated even though it was not specified when setting the option. If the server is started with --binlog-do-db=sales, the following UPDATE statement is logged even though prices was not included when setting --binlog-do-db:

            
    USE sales;
    UPDATE prices.discounts SET percentage = percentage + 10;
    

    Because sales is the default database when the UPDATE statement is issued, the UPDATE is logged.

    Row-based logging.  Logging is restricted to database db_name. Only changes to tables belonging to db_name are logged; the default database has no effect on this. Suppose that the server is started with --binlog-do-db=sales and row-based logging is in effect, and then the following statements are executed:

    USE prices;
    UPDATE sales.february SET amount=amount+100;
    

    The changes to the february table in the sales database are logged in accordance with the UPDATE statement; this occurs whether or not the USE statement was issued. However, when using the row-based logging format and --binlog-do-db=sales, changes made by the following UPDATE are not logged:

    USE prices;
    UPDATE prices.march SET amount=amount-25;
    

    Even if the USE prices statement were changed to USE sales, the UPDATE statement's effects would still not be written to the binary log.

    Another important difference in --binlog-do-db handling for statement-based logging as opposed to the row-based logging occurs with regard to statements that refer to multiple databases. Suppose that the server is started with --binlog-do-db=db1, and the following statements are executed:

    USE db1;
    UPDATE db1.table1 SET col1 = 10, db2.table2 SET col2 = 20;
    

    If you are using statement-based logging, the updates to both tables are written to the binary log. However, when using the row-based format, only the changes to table1 are logged; table2 is in a different database, so it is not changed by the UPDATE. Now suppose that, instead of the USE db1 statement, a USE db4 statement had been used:

    USE db4;
    UPDATE db1.table1 SET col1 = 10, db2.table2 SET col2 = 20;
    

    In this case, the UPDATE statement is not written to the binary log when using statement-based logging. However, when using row-based logging, the change to table1 is logged, but not that to table2—in other words, only changes to tables in the database named by --binlog-do-db are logged, and the choice of default database has no effect on this behavior.

  • --binlog-ignore-db=db_name

    Command-Line Format--binlog-ignore-db=name
    Permitted ValuesTypestring

    This option affects binary logging in a manner similar to the way that --replicate-ignore-db affects replication.

    The effects of this option depend on whether the statement-based or row-based logging format is in use, in the same way that the effects of --replicate-ignore-db depend on whether statement-based or row-based replication is in use. You should keep in mind that the format used to log a given statement may not necessarily be the same as that indicated by the value of binlog_format. For example, DDL statements such as CREATE TABLE and ALTER TABLE are always logged as statements, without regard to the logging format in effect, so the following statement-based rules for --binlog-ignore-db always apply in determining whether or not the statement is logged.

    Statement-based logging.  Tells the server to not log any statement where the default database (that is, the one selected by USE) is db_name.

    Prior to MySQL 5.7.2, this option caused any statements containing fully qualified table names not to be logged if there was no default database specified (that is, when SELECT DATABASE() returned NULL). In MySQL 5.7.2 and later, when there is no default database, no --binlog-ignore-db options are applied, and such statements are always logged. (Bug #11829838, Bug #60188)

    Row-based format.  Tells the server not to log updates to any tables in the database db_name. The current database has no effect.

    When using statement-based logging, the following example does not work as you might expect. Suppose that the server is started with --binlog-ignore-db=sales and you issue the following statements:

    USE prices;
    UPDATE sales.january SET amount=amount+1000;
    

    The UPDATE statement is logged in such a case because --binlog-ignore-db applies only to the default database (determined by the USE statement). Because the sales database was specified explicitly in the statement, the statement has not been filtered. However, when using row-based logging, the UPDATE statement's effects are not written to the binary log, which means that no changes to the sales.january table are logged; in this instance, --binlog-ignore-db=sales causes all changes made to tables in the master's copy of the sales database to be ignored for purposes of binary logging.

    To specify more than one database to ignore, use this option multiple times, once for each database. Because database names can contain commas, the list will be treated as the name of a single database if you supply a comma-separated list.

    You should not use this option if you are using cross-database updates and you do not want these updates to be logged.

Checksum options.  MySQL 5.7 supports reading and writing of binary log checksums. These are enabled using the two options listed here:

  • --binlog-checksum={NONE|CRC32}

    Command-Line Format--binlog-checksum=type
    Permitted ValuesTypestring
    DefaultCRC32
    Valid ValuesNONE
    CRC32

    Enabling this option causes the master to write checksums for events written to the binary log. Set to NONE to disable, or the name of the algorithm to be used for generating checksums; currently, only CRC32 checksums are supported, and CRC32 is the default.

  • --master-verify-checksum={0|1}

    Command-Line Format--master-verify-checksum=name
    Permitted ValuesTypeboolean
    DefaultOFF

    Enabling this option causes the master to verify events from the binary log using checksums, and to stop with an error in the event of a mismatch. Disabled by default.

To control reading of checksums by the slave (from the relay) log, use the --slave-sql-verify-checksum option.

Testing and debugging options.  The following binary log options are used in replication testing and debugging. They are not intended for use in normal operations.

  • --max-binlog-dump-events=N

    Command-Line Format--max-binlog-dump-events=#
    Permitted ValuesTypeinteger
    Default0

    This option is used internally by the MySQL test suite for replication testing and debugging.

  • --sporadic-binlog-dump-fail

    Command-Line Format--sporadic-binlog-dump-fail
    Permitted ValuesTypeboolean
    DefaultFALSE

    This option is used internally by the MySQL test suite for replication testing and debugging.

  • --binlog-rows-query-log-events

    Command-Line Format--binlog-rows-query-log-events
    Permitted ValuesTypeboolean
    DefaultFALSE

    This option enables binlog_rows_query_log_events.

System Variables Used with Binary Logging

The following list describes system variables for controlling binary logging. They can be set at server startup and some of them can be changed at runtime using SET. Server options used to control binary logging are listed earlier in this section. For information about the sql_log_bin and sql_log_off variables, see Section 6.1.5, “Server System Variables”.

  • binlog_cache_size

    Command-Line Format--binlog_cache_size=#
    System VariableNamebinlog_cache_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default32768
    Min Value4096
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default32768
    Min Value4096
    Max Value18446744073709551615

    The size of the cache to hold changes to the binary log during a transaction. A binary log cache is allocated for each client if the server supports any transactional storage engines and if the server has the binary log enabled (--log-bin option). If you often use large transactions, you can increase this cache size to get better performance. The Binlog_cache_use and Binlog_cache_disk_use status variables can be useful for tuning the size of this variable. See Section 6.4.4, “The Binary Log”.

    binlog_cache_size sets the size for the transaction cache only; the size of the statement cache is governed by the binlog_stmt_cache_size system variable.

  • binlog_checksum

    System VariableNamebinlog_checksum
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypestring
    DefaultCRC32
    Valid ValuesNONE
    CRC32

    When enabled, this variable causes the master to write a checksum for each event in the binary log. binlog_checksum supports the values NONE (disabled) and CRC32. The default is CRC32.

    When binlog_checksum is disabled (value NONE), the server verifies that it is writing only complete events to the binary log by writing and checking the event length (rather than a checksum) for each event.

    Changing the value of this variable causes the binary log to be rotated; checksums are always written to an entire binary log file, and never to only part of one.

    Setting this variable on the master to a value unrecognized by the slave causes the slave to set its own binlog_checksum value to NONE, and to stop replication with an error. (Bug #13553750, Bug #61096) If backward compatibility with older slaves is a concern, you may want to set the value explicitly to NONE.

  • binlog_direct_non_transactional_updates

    Command-Line Format--binlog_direct_non_transactional_updates[=value]
    System VariableNamebinlog_direct_non_transactional_updates
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    Due to concurrency issues, a slave can become inconsistent when a transaction contains updates to both transactional and nontransactional tables. MySQL tries to preserve causality among these statements by writing nontransactional statements to the transaction cache, which is flushed upon commit. However, problems arise when modifications done to nontransactional tables on behalf of a transaction become immediately visible to other connections because these changes may not be written immediately into the binary log.

    The binlog_direct_non_transactional_updates variable offers one possible workaround to this issue. By default, this variable is disabled. Enabling binlog_direct_non_transactional_updates causes updates to nontransactional tables to be written directly to the binary log, rather than to the transaction cache.

    binlog_direct_non_transactional_updates works only for statements that are replicated using the statement-based binary logging format; that is, it works only when the value of binlog_format is STATEMENT, or when binlog_format is MIXED and a given statement is being replicated using the statement-based format. This variable has no effect when the binary log format is ROW, or when binlog_format is set to MIXED and a given statement is replicated using the row-based format.

    Important

    Before enabling this variable, you must make certain that there are no dependencies between transactional and nontransactional tables; an example of such a dependency would be the statement INSERT INTO myisam_table SELECT * FROM innodb_table. Otherwise, such statements are likely to cause the slave to diverge from the master.

    In MySQL 5.7, this variable has no effect when the binary log format is ROW or MIXED. (Bug #51291)

  • binlog_error_action

    Introduced5.7.6
    Command-Line Format--binlog_error_action[=value]
    System VariableNamebinlog_error_action
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    DefaultIGNORE_ERROR
    Valid ValuesIGNORE_ERROR
    ABORT_SERVER
    Permitted Values (>= 5.7.7)Typeenumeration
    DefaultABORT_SERVER
    Valid ValuesIGNORE_ERROR
    ABORT_SERVER

    Controls what happens when the server encounters an error such as not being able to write to, flush or synchronize the binary log, which can cause the master's log to become inconsistent and replication slaves to lose synchronization.

    In MySQL 5.7.7 and later, this variable defaults to ABORT_SERVER, which makes the server halt logging and shut down whenever it encounters such an error with the binary log. Upon server restart, all of the previously prepared and binary logged transactions are committed, while any transactions which were prepared but not binary logged due to the error are aborted.

    When binlog_error_action is set to IGNORE_ERROR, if the server encounters such an error it continues the ongoing transaction, logs the error then halts logging, and continues performing updates. To resume binary logging log_bin must be enabled again. This provides backward compatibility with older versions of MySQL.

    In previous releases this variable was named binlogging_impossible_mode.

  • binlog_format

    Command-Line Format--binlog-format=format
    System VariableNamebinlog_format
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted Values (<= 5.7.6)Typeenumeration
    DefaultSTATEMENT
    Valid ValuesROW
    STATEMENT
    MIXED
    Permitted Values (>= 5.7.7)Typeenumeration
    DefaultROW
    Valid ValuesROW
    STATEMENT
    MIXED

    This variable sets the binary logging format, and can be any one of STATEMENT, ROW, or MIXED. See Section 18.2.1, “Replication Formats”. binlog_format is set by the --binlog-format option at startup, or by the binlog_format variable at runtime.

    Note

    While you can change the logging format at runtime, it is not recommended that you change it while replication is ongoing. This is due in part to the fact that slaves do not honor the master's binlog_format setting; a given MySQL Server can change only its own logging format.

    Prior to MySQL 5.7.7, the default format was STATEMENT. In MySQL 5.7.7 and later the default is ROW. Exception: In MySQL Cluster, the default is MIXED; statement-based replication is not supported for MySQL Cluster.

    You must have the SUPER privilege to set either the global or session binlog_format value.

    The rules governing when changes to this variable take effect and how long the effect lasts are the same as for other MySQL server system variables. For more information, see Section 14.7.4.1, “SET Syntax for Variable Assignment”.

    When MIXED is specified, statement-based replication is used, except for cases where only row-based replication is guaranteed to lead to proper results. For example, this happens when statements contain user-defined functions (UDF) or the UUID() function. An exception to this rule is that MIXED always uses statement-based replication for stored functions and triggers.

    There are exceptions when you cannot switch the replication format at runtime:

    • From within a stored function or a trigger.

    • If the session is currently in row-based replication mode and has open temporary tables.

    • From within a transaction.

    Trying to switch the format in those cases results in an error.

    The binary log format affects the behavior of the following server options:

    These effects are discussed in detail in the descriptions of the individual options.

  • binlog_group_commit_sync_delay

    Introduced5.7.5
    Command-Line Format--binlog-group-commit-sync-delay=#
    System VariableNamebinlog_group_commit_sync_delay
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0
    Min Value0
    Max Value1000000

    Controls how many microseconds the binary log commit waits before synchronizing the binary log file to disk. By default binlog-group-commit-sync-delay is set to 0, meaning that there is no delay. Setting binlog-group-commit-sync-delay to a microsecond delay enables more transactions to be synchronized together to disk at once, reducing the overall time to commit a group of transactions because the larger groups require fewer time units per group. With the correct tuning, this can increase slave performance without compromising the master's throughput.

  • binlog_group_commit_sync_no_delay_count

    Introduced5.7.5
    Command-Line Format--binlog-group-commit-sync-no-delay-count=#
    System VariableNamebinlog_group_commit_sync_no_delay_count
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0
    Min Value0
    Max Value1000000

    The maximum number of transactions to wait for before aborting the current delay as specified by binlog-group-commit-sync-delay. If binlog-group-commit-sync-delay is set to 0, then this option has no effect.

  • binlogging_impossible_mode

    Introduced5.7.5
    Deprecated5.7.6
    Command-Line Format--binlogging_impossible_mode[=value]
    System VariableNamebinlogging_impossible_mode
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    DefaultIGNORE_ERROR
    Valid ValuesIGNORE_ERROR
    ABORT_SERVER

    This option is deprecated and will be removed in a future MySQL release. Use the renamed binlog_error_action to control what happens when the server cannot write to the binary log.

  • binlog_max_flush_queue_time

    Deprecated5.7.9
    System VariableNamebinlog_max_flush_queue_time
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default0
    Min Value0
    Max Value100000

    Formerly, this controlled the time in microseconds to continue reading transactions from the flush queue before proceeding with group commit. In MySQL 5.7, this variable no longer has any effect.

    binlog_max_flush_queue_time is deprecated as of MySQL 5.7.9, and is marked for eventual removal in a future MySQL release.

  • binlog_order_commits

    System VariableNamebinlog_order_commits
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultON

    When this variable is enabled on a master (the default), transactions are externalized in the same order as they are written to the binary log. If disabled, transactions may be committed in parallel. In some cases, disabling this variable might produce a performance increment.

  • binlog_row_image

    Command-Line Format--binlog-row-image=image_type
    System VariableNamebinlog_row_image=image_type
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    Defaultfull
    Valid Valuesfull (Log all columns)
    minimal (Log only changed columns, and columns needed to identify rows)
    noblob (Log all columns, except for unneeded BLOB and TEXT columns)

    In MySQL row-based replication, each row change event contains two images, a before image whose columns are matched against when searching for the row to be updated, and an after image containing the changes. Normally, MySQL logs full rows (that is, all columns) for both the before and after images. However, it is not strictly necessary to include every column in both images, and we can often save disk, memory, and network usage by logging only those columns which are actually required.

    Note

    When deleting a row, only the before image is logged, since there are no changed values to propagate following the deletion. When inserting a row, only the after image is logged, since there is no existing row to be matched. Only when updating a row are both the before and after images required, and both written to the binary log.

    For the before image, it is necessary only that the minimum set of columns required to uniquely identify rows is logged. If the table containing the row has a primary key, then only the primary key column or columns are written to the binary log. Otherwise, if the table has a unique key all of whose columns are NOT NULL, then only the columns in the unique key need be logged. (If the table has neither a primary key nor a unique key without any NULL columns, then all columns must be used in the before image, and logged.) In the after image, it is necessary to log only the columns which have actually changed.

    You can cause the server to log full or minimal rows using the binlog_row_image system variable. This variable actually takes one of three possible values, as shown in the following list:

    • full: Log all columns in both the before image and the after image.

    • minimal: Log only those columns in the before image that are required to identify the row to be changed; log only those columns in the after image that are actually changed.

    • noblob: Log all columns (same as full), except for BLOB and TEXT columns that are not required to identify rows, or that have not changed.

    Note

    This variable is not supported by MySQL Cluster; setting it has no effect on the logging of NDB tables.

    The default value is full.

    In MySQL 5.5 and earlier, full row images are always used for both before images and after images. If you need to replicate from a newer master to a slave running MySQL 5.5 or earlier, the master should always use this value.

    When using minimal or noblob, deletes and updates are guaranteed to work correctly for a given table if and only if the following conditions are true for both the source and destination tables:

    • All columns must be present and in the same order; each column must use the same data type as its counterpart in the other table.

    • The tables must have identical primary key definitions.

    (In other words, the tables must be identical with the possible exception of indexes that are not part of the tables' primary keys.)

    If these conditions are not met, it is possible that the primary key column values in the destination table may prove insufficient to provide a unique match for a delete or update. In this event, no warning or error is issued; the master and slave silently diverge, thus breaking consistency.

    Setting this variable has no effect when the binary logging format is STATEMENT. When binlog_format is MIXED, the setting for binlog_row_image is applied to changes that are logged using row-based format, but this setting no effect on changes logged as statements.

    Setting binlog_row_image on either the global or session level does not cause an implicit commit; this means that this variable can be changed while a transaction is in progress without affecting the transaction.

  • binlog_rows_query_log_events

    System VariableNamebinlog_rows_query_log_events
    Variable ScopeGlobal, Session
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultFALSE

    The binlog_rows_query_log_events system variable affects row-based logging only. When enabled, it causes the MySQL Server to write informational log events such as row query log events into its binary log. This information can be used for debugging and related purposes; such as obtaining the original query issued on the master when it cannot be reconstructed from the row updates.

    These events are normally ignored by MySQL programs reading the binary log and so cause no issues when replicating or restoring from backup. To view them, increase the verbosity level by using mysqlbinlog's --verbose option twice, either as "-vv" or "--verbose --verbose".

  • binlog_stmt_cache_size

    Command-Line Format--binlog_stmt_cache_size=#
    System VariableNamebinlog_stmt_cache_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (32-bit platforms)Typeinteger
    Default32768
    Min Value4096
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default32768
    Min Value4096
    Max Value18446744073709551615

    This variable determines the size of the cache for the binary log to hold nontransactional statements issued during a transaction. Separate binary log transaction and statement caches are allocated for each client if the server supports any transactional storage engines and if the server has the binary log enabled (--log-bin option). If you often use large nontransactional statements during transactions, you can increase this cache size to get better performance. The Binlog_stmt_cache_use and Binlog_stmt_cache_disk_use status variables can be useful for tuning the size of this variable. See Section 6.4.4, “The Binary Log”.

    The binlog_cache_size system variable sets the size for the transaction cache.

  • log_bin

    System VariableNamelog_bin
    Variable ScopeGlobal
    Dynamic VariableNo

    Whether the binary log is enabled. If the --log-bin option is used, then the value of this variable is ON; otherwise it is OFF. This variable reports only on the status of binary logging (enabled or disabled); it does not actually report the value to which --log-bin is set.

    See Section 6.4.4, “The Binary Log”.

  • log_bin_basename

    System VariableNamelog_bin_basename
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypefile name
    Defaultdatadir + '/' + hostname + '-bin'

    Holds the name and complete path to the binary log file. Unlike the log_bin system variable, log_bin_basename reflects the name set with the --log-bin server option.

  • log_bin_index

    System VariableNamelog_bin_index
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypefile name

    The index file for binary log file names.

  • log_bin_use_v1_row_events

    Command-Line Format--log-bin-use-v1-row-events[={0|1}]
    System VariableNamelog_bin_use_v1_row_events
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeboolean
    Default0

    Shows whether Version 2 binary logging is in use. A value of 1 shows that the server is writing the binary log using Version 1 logging events (the only version of binary log events used in previous releases), and thus producing a binary log that can be read by older slaves. 0 indicates that Version 2 binary log events are in use.

    This variable is read-only. To switch between Version 1 and Version 2 binary event binary logging, it is necessary to restart mysqld with the --log-bin-use-v1-row-events option.

    Other than when performing upgrades of MySQL Cluster Replication, --log-bin-use-v1-events is chiefly of interest when setting up replication conflict detection and resolution using NDB$EPOCH_TRANS(), which requires Version 2 binary row event logging. Thus, this option and --ndb-log-transaction-id are not compatible.

    Note

    MySQL NDB Cluster 7.5 uses Version 2 binary log row events by default. You should keep this mind when planning upgrades or downgrades, and for setups using MySQL Cluster Replication.

    For more information, see Section 20.6.11, “NDB Cluster Replication Conflict Resolution”.

  • log_slave_updates

    Command-Line Format--log-slave-updates
    System VariableNamelog_slave_updates
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeboolean
    DefaultFALSE

    Whether updates received by a slave server from a master server should be logged to the slave's own binary log. Binary logging must be enabled on the slave for this variable to have any effect. See Section 18.1.6, “Replication and Binary Logging Options and Variables”.

  • log_statements_unsafe_for_binlog

    Introduced5.7.11
    System VariableNamelog_statements_unsafe_for_binlog
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultON

    If error 1592 is encountered, controls whether the generated warnings are added to the error log or not.

  • master_verify_checksum

    System VariableNamemaster_verify_checksum
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeboolean
    DefaultOFF

    Enabling this variable causes the master to examine checksums when reading from the binary log. master_verify_checksum is disabled by default; in this case, the master uses the event length from the binary log to verify events, so that only complete events are read from the binary log.

  • max_binlog_cache_size

    Command-Line Format--max_binlog_cache_size=#
    System VariableNamemax_binlog_cache_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default18446744073709551615
    Min Value4096
    Max Value18446744073709551615

    If a transaction requires more than this many bytes of memory, the server generates a Multi-statement transaction required more than 'max_binlog_cache_size' bytes of storage error. The minimum value is 4096. The maximum possible value is 16EB (exabytes). The maximum recommended value is 4GB; this is due to the fact that MySQL currently cannot work with binary log positions greater than 4GB.

    max_binlog_cache_size sets the size for the transaction cache only; the upper limit for the statement cache is governed by the max_binlog_stmt_cache_size system variable.

    In MySQL 5.7, the visibility to sessions of max_binlog_cache_size matches that of the binlog_cache_size system variable; in other words, changing its value effects only new sessions that are started after the value is changed.

  • max_binlog_size

    Command-Line Format--max_binlog_size=#
    System VariableNamemax_binlog_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default1073741824
    Min Value4096
    Max Value1073741824

    If a write to the binary log causes the current log file size to exceed the value of this variable, the server rotates the binary logs (closes the current file and opens the next one). The minimum value is 4096 bytes. The maximum and default value is 1GB.

    A transaction is written in one chunk to the binary log, so it is never split between several binary logs. Therefore, if you have big transactions, you might see binary log files larger than max_binlog_size.

    If max_relay_log_size is 0, the value of max_binlog_size applies to relay logs as well.

  • max_binlog_stmt_cache_size

    Command-Line Format--max_binlog_stmt_cache_size=#
    System VariableNamemax_binlog_stmt_cache_size
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default18446744073709547520
    Min Value4096
    Max Value18446744073709547520

    If nontransactional statements within a transaction require more than this many bytes of memory, the server generates an error. The minimum value is 4096. The maximum and default values are 4GB on 32-bit platforms and 16EB (exabytes) on 64-bit platforms.

    max_binlog_stmt_cache_size sets the size for the statement cache only; the upper limit for the transaction cache is governed exclusively by the max_binlog_cache_size system variable.

  • sync_binlog

    Command-Line Format--sync-binlog=#
    System VariableNamesync_binlog
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (>= 5.7.7)Typeinteger
    Default1
    Min Value0
    Max Value4294967295
    Permitted Values (32-bit platforms)Typeinteger
    Default0
    Min Value0
    Max Value4294967295
    Permitted Values (64-bit platforms)Typeinteger
    Default0
    Min Value0
    Max Value4294967295

    Controls the number of binary log commit groups to collect before synchronizing the binary log to disk. When sync_binlog=0, the binary log is never synchronized to disk, and when sync_binlog is set to a value greater than 0 this number of binary log commit groups is periodically synchronized to disk. When sync_binlog=1, all transactions are synchronized to the binary log before they are committed. Therefore, even in the event of an unexpected restart, any transactions that are missing from the binary log are only in prepared state. This causes the server's automatic recovery routine to roll back those transactions. This guarantees that no transaction is lost from the binary log, and is the safest option. However this can have a negative impact on performance because of an increased number of disk writes. Using a higher value improves performance, but with the increased risk of data loss.

    When sync_binlog=0 or sync_binlog is greater than 1, transactions are committed without having been synchronized to disk. Therefore, in the event of a power failure or operating system crash, it is possible that the server has committed some transactions that have not been synchronized to the binary log. Therefore it is impossible for the recovery routine to recover these transactions and they will be lost from the binary log.

    Prior to MySQL 5.7.7, the default value of sync_binlog was 0, which configures no synchronizing to disk—in this case, the server relies on the operating system to flush the binary log's contents from time to time as for any other file. MySQL 5.7.7 and later use a default value of 1, which is the safest choice, but as noted above can impact performance.

18.1.6.5 Global Transaction ID Options and Variables

Startup Options Used with GTID Replication

System Variables Used with GTID Replication

The MySQL Server options and system variables described in this section are used to monitor and control Global Transaction Identifiers (GTIDs).

For additional information, see Section 18.1.3, “Replication with Global Transaction Identifiers”.

Startup Options Used with GTID Replication

The following server startup options are used with GTID-based replication:

  • --enforce-gtid-consistency

    Command-Line Format--enforce-gtid-consistency[=value]
    System Variable (<= 5.7.5)Nameenforce_gtid_consistency
    Variable ScopeGlobal
    Dynamic VariableNo
    System Variable (>= 5.7.6)Nameenforce_gtid_consistency
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (<= 5.7.5)Typeboolean
    Defaultfalse
    Permitted Values (>= 5.7.6)Typeenumeration
    DefaultOFF
    Valid ValuesOFF
    ON
    WARN

    When enabled, the server enforces GTID consistency by allowing execution of only statements that can be safely logged using a GTID. You must set this option to ON before enabling GTID based replication.

    The values that --enforce-gtid-consistency can be configured to are:

    • OFF: all transactions are allowed to violate GTID consistency.

    • ON: no transaction is allowed to violate GTID consistency.

    • WARN: all transactions are allowed to violate GTID consistency, but a warning is generated in this case. Added in MySQL 5.7.6.

    Setting --enforce-gtid-consistency without a value is an alias for --enforce-gtid-consistency=ON. This impacts on the behavior of the variable, see enforce_gtid_consistency.

    Only statements that can be logged using GTID safe statements can be logged when enforce-gtid-consistency is set to ON, so the operations listed here cannot be used with this option:

    • CREATE TABLE ... SELECT statements

    • CREATE TEMPORARY TABLE or DROP TEMPORARY TABLE statements inside transactions

    • Transactions or statements that update both transactional and nontransactional tables. There is an exception that nontransactional DML is allowed in the same transaction or in the same statement as transactional DML, if all nontransactional tables are temporary.

    For more information, see Section 18.1.3.4, “Restrictions on Replication with GTIDs”.

  • --executed-gtids-compression-period

    Introduced5.7.5
    Deprecated5.7.6
    Command-Line Format--executed-gtids-compression-period=#
    Permitted ValuesTypeinteger
    Default1000
    Min Value0
    Max Value4294967295

    This option is deprecated and will be removed in a future MySQL release. Use the renamed gtid_executed_compression_period to control how the gtid_executed table is compressed.

  • --gtid-mode

    Command-Line Format--gtid-mode=MODE
    System Variable (<= 5.7.5)Namegtid_mode
    Variable ScopeGlobal
    Dynamic VariableNo
    System Variable (>= 5.7.6)Namegtid_mode
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (<= 5.7.5)Typeenumeration
    DefaultOFF
    Valid ValuesOFF
    UPGRADE_STEP_1
    UPGRADE_STEP_2
    ON
    Permitted Values (>= 5.7.6)Typeenumeration
    DefaultOFF
    Valid ValuesOFF
    OFF_PERMISSIVE
    ON_PERMISSIVE
    ON

    This option specifies whether global transaction identifiers (GTIDs) are used to identify transactions. Setting this option to --gtid-mode=ON requires that enforce-gtid-consistency be set to ON. Prior to MySQL 5.7.6 the gtid_mode variable which this option controls could only be set at server startup. In MySQL 5.7.6 and later the gtid_mode variable is dynamic and enables GTID based replication to be configured online. Before using this feature, see Section 18.1.5, “Changing Replication Modes on Online Servers”.

    Prior to MySQL 5.7.5, starting the server with --gtid-mode=ON required that the server also be started with the --log-bin, --log-slave-updates, options. In versions of MySQL 5.7.5 and later this is not a requirement. See mysql.gtid_executed Table.

  • --gtid-executed-compression-period

    Introduced5.7.6
    Command-Line Format--gtid-executed-compression-period=#
    Permitted ValuesTypeinteger
    Default1000
    Min Value0
    Max Value4294967295

    Compress the mysql.gtid_executed table each time this many transactions have taken place. A setting of 0 means that this table is not compressed. No compression of the table occurs when binary logging is enabled, therefore the option has no effect unless log_bin is OFF.

    See mysql.gtid_executed Table Compression, for more information.

    In MySQL version 5.7.5, this variable was added as executed_gtids_compression_period and in MySQL version 5.7.6 it was renamed to gtid_executed_compression_period.

System Variables Used with GTID Replication

The following system variables are used with GTID-based replication:

  • binlog_gtid_simple_recovery

    Introduced5.7.6
    Command-Line Format--binlog-gtid-simple-recovery
    System VariableNamebinlog_gtid_simple_recovery
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeboolean
    DefaultFALSE
    Permitted Values (>= 5.7.7)Typeboolean
    DefaultTRUE

    This variable controls how binary log files are iterated during the search for GTIDs when MySQL starts or restarts. In MySQL version 5.7.5, this variable was added as simplified_binlog_gtid_recovery and in MySQL version 5.7.6 it was renamed to binlog_gtid_simple_recovery.

    When binlog_gtid_simple_recovery=FALSE, the method of iterating the binary log files is:

    • To initialize gtid_executed, binary log files are iterated from the newest file, stopping at the first binary log that has any Previous_gtids_log_event. All GTIDs from Previous_gtids_log_event and Gtid_log_events are read from this binary log file. This GTID set is stored internally and called gtids_in_binlog. The value of gtid_executed is computed as the union of this set and the GTIDs stored in the mysql.gtid_executed table.

      This process could take a long time if you had a large number of binary log files without GTID events, for example created when gtid_mode=OFF.

    • To initialize gtid_purged, binary log files are iterated from the oldest to the newest, stopping at the first binary log that contains either a Previous_gtids_log_event that is non-empty (that has at least one GTID) or that has at least one Gtid_log_event. From this binary log it reads Previous_gtids_log_event. This GTID set is subtracted from gtids_in_binlog and the result stored in the internal variable gtids_in_binlog_not_purged. The value of gtid_purged is initialized to the value of gtid_executed, minus gtids_in_binlog_not_purged.

    When binlog_gtid_simple_recovery=TRUE, which is the default in MySQL 5.7.7 and later, the server iterates only the oldest and the newest binary log files and the values of gtid_purged and gtid_executed are computed based only on Previous_gtids_log_event or Gtid_log_event found in these files. This ensures only two binary log files are iterated during server restart or when binary logs are being purged.

    Note

    If this option is enabled, gtid_executed and gtid_purged may be initialized incorrectly in the following situations:

    • The newest binary log was generated by MySQL 5.7.5 or older, and gtid_mode was ON for some binary logs but OFF for the newest binary log.

    • A SET GTID_PURGED statement was issued on a MySQL version prior to 5.7.7, and the binary log that was active at the time of the SET GTID_PURGED has not yet been purged.

    If an incorrect GTID set is computed in either situation, it will remain incorrect even if the server is later restarted, regardless of the value of this option.

  • enforce_gtid_consistency

    Command-Line Format--enforce-gtid-consistency[=value]
    System Variable (<= 5.7.5)Nameenforce_gtid_consistency
    Variable ScopeGlobal
    Dynamic VariableNo
    System Variable (>= 5.7.6)Nameenforce_gtid_consistency
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (<= 5.7.5)Typeboolean
    Defaultfalse
    Permitted Values (>= 5.7.6)Typeenumeration
    DefaultOFF
    Valid ValuesOFF
    ON
    WARN

    Depending on the value of this variable, the server enforces GTID consistency by allowing execution of only statements that can be safely logged using a GTID. You must set this variable to ON before enabling GTID based replication.

    The values that enforce_gtid_consistency can be configured to are:

    • OFF: all transactions are allowed to violate GTID consistency.

    • ON: no transaction is allowed to violate GTID consistency.

    • WARN: all transactions are allowed to violate GTID consistency, but a warning is generated in this case. Added in MySQL 5.7.6.

    For more information on statements that can be logged using GTID based replication, see --enforce-gtid-consistency.

    Prior to MySQL 5.7.6, the boolean enforce-gtid-consistency defaulted to OFF. To maintain compatibility with previous versions, in MySQL 5.7.6 the enumeration defaults to OFF, and setting --enforce-gtid-consistency without a value is interpreted as setting the value to ON. The variable also has multiple textual aliases for the values: 0=OFF=FALSE, 1=ON=TRUE,2=WARN. This differs from other enumeration types but maintains compatibility with the boolean type used in previous versions. These changes impact on what is returned by the variable. Using SELECT @@ENFORCE_GTID_CONSISTENCY, SHOW VARIABLES LIKE 'ENFORCE_GTID_CONSISTENCY', and SELECT * FROM INFORMATION_SCHEMA.VARIABLES WHERE 'VARIABLE_NAME' = 'ENFORCE_GTID_CONSISTENCY', all return the textual form, not the numeric form. This is an incompatible change, since @@ENFORCE_GTID_CONSISTENCY returns the numeric form for booleans but returns the textual form for SHOW and the Information Schema.

  • executed_gtids_compression_period

    Introduced5.7.5
    Deprecated5.7.6
    System Variable (>= 5.7.5)Nameexecuted_gtids_compression_period
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default1000
    Min Value0
    Max Value4294967295

    This option is deprecated and will be removed in a future MySQL release. Use the renamed gtid_executed_compression_period to control how the gtid_executed table is compressed.

  • gtid_executed

    System VariableNamegtid_executed
    Variable ScopeGlobal, Session
    Dynamic VariableNo
    System Variable (>= 5.7.7)Namegtid_executed
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypestring

    When used with global scope, this variable contains a representation of the set of all transactions executed on the server and GTIDs that have been set by a SET gtid_purged statement. This is the same as the value of the Executed_Gtid_Set column in the output of SHOW MASTER STATUS and SHOW SLAVE STATUS. The value of this variable is a GTID set, see GTID Sets for more information.

    When the server starts, @@global.gtid_executed is initialized. See binlog_gtid_simple_recovery for more information on how binary logs are iterated to populate gtid_executed. GTIDs are then added to the set as transactions are executed, or if any SET gtid_purged statement is executed.

    The set of transactions that can be found in the binary logs at any given time is equal to GTID_SUBTRACT(@@global.gtid_executed, @@global.gtid_purged); that is, to all transactions in the binary log that have not yet been purged.

    Issuing RESET MASTER causes the global value (but not the session value) of this variable to be reset to an empty string. GTIDs are not otherwise removed from this set other than when the set is cleared due to RESET MASTER.

    Prior to MySQL 5.7.7, this variable could also be used with session scope, where it contained a representation of the set of transactions that are written to the cache in the current session. The session scope was deprecated in MySQL 5.7.7.

  • gtid_executed_compression_period

    Introduced5.7.6
    System Variable (>= 5.7.6)Namegtid_executed_compression_period
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypeinteger
    Default1000
    Min Value0
    Max Value4294967295

    Compress the mysql.gtid_executed table each time this many transactions have been processed. A setting of 0 means that this table is not compressed. Since no compression of the table occurs when using the binary log, setting the value of the variable has no effect unless binary logging is disabled.

    See mysql.gtid_executed Table Compression, for more information.

    In MySQL version 5.7.5, this variable was added as executed_gtids_compression_period and in MySQL version 5.7.6 it was renamed to gtid_executed_compression_period.

  • gtid_mode

    System Variable (<= 5.7.5)Namegtid_mode
    Variable ScopeGlobal
    Dynamic VariableNo
    System Variable (>= 5.7.6)Namegtid_mode
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted Values (<= 5.7.5)Typeenumeration
    DefaultOFF
    Valid ValuesOFF
    UPGRADE_STEP_1
    UPGRADE_STEP_2
    ON
    Permitted Values (>= 5.7.6)Typeenumeration
    DefaultOFF
    Valid ValuesOFF
    OFF_PERMISSIVE
    ON_PERMISSIVE
    ON

    Controls whether GTID based logging is enabled and what type of transactions the logs can contain. Prior to MySQL 5.7.6 this variable was read-only and was set using the --gtid-mode option only. MySQL 5.7.6 enables this variable to be set dynamically. You must have the SUPER privilege to set this variable. enforce_gtid_consistency must be true before you can set gtid_mode=ON. Before modifying this variable, see Section 18.1.5, “Changing Replication Modes on Online Servers”.

    Transactions logged in MySQL 5.7.6 and later can be either anonymous or use GTIDs. Anonymous transactions rely on binary log file and position to identify specific transactions. GTID transactions have a unique identifier that is used to refer to transactions. The OFF_PERMISSIVE and ON_PERMISSIVE modes added in MySQL 5.7.6 permit a mix of these transaction types in the topology. The different modes are now:

    • OFF: Both new and replicated transactions must be anonymous.

    • OFF_PERMISSIVE: New transactions are anonymous. Replicated transactions can be either anonymous or GTID transactions.

    • ON_PERMISSIVE: New transactions are GTID transactions. Replicated transactions can be either anonymous or GTID transactions.

    • ON: Both new and replicated transactions must be GTID transactions.

    Changes from one value to another can only be one step at a time. For example, if gtid_mode is currently set to OFF_PERMISSIVE, it is possible to change to OFF or ON_PERMISSIVE but not to ON.

    In MySQL 5.7.6 and later, the values of gtid_purged and gtid_executed are persistent regardless of the value of gtid_mode. Therefore even after changing the value of gtid_mode, these variables contain the correct values. In MySQL 5.7.5 and earlier, the values of gtid_purged and gtid_executed are not persistent while gtid_mode=OFF. Therefore, after changing gtid_mode to OFF, once all binary logs containing GTIDs are purged, the values of these variables are lost.

  • gtid_next

    System VariableNamegtid_next
    Variable ScopeSession
    Dynamic VariableYes
    Permitted ValuesTypeenumeration
    DefaultAUTOMATIC
    Valid ValuesAUTOMATIC
    ANONYMOUS
    UUID:NUMBER

    This variable is used to specify whether and how the next GTID is obtained. gtid_next can take any of the following values:

    • AUTOMATIC: Use the next automatically-generated global transaction ID.

    • ANONYMOUS: Transactions do not have global identifiers, and are identified by file and position only.

    • A global transaction ID in UUID:NUMBER format.

    Exactly which of the above options are valid depends on the setting of gtid_mode, see Section 18.1.5.1, “Replication Mode Concepts” for more information. Setting this variable has no effect if gtid_mode is OFF.

    After this variable has been set to UUID:NUMBER, and a transaction has been committed or rolled back, an explicit SET GTID_NEXT statement must again be issued before any other statement.

    In MySQL 5.7.5 and later, DROP TABLE or DROP TEMPORARY TABLE fails with an explicit error when used on a combination of nontemporary tables with temporary tables, or of temporary tables using transactional storage engines with temporary tables using nontransactional storage engines. Prior to MySQL 5.7.5, when GTIDs were enabled but gtid_next was not AUTOMATIC, DROP TABLE did not work correctly when used with either of these combinations of tables. (Bug #17620053)

    In MySQL 5.7.1, you cannot execute any of the statements CHANGE MASTER TO, START SLAVE, STOP SLAVE, REPAIR TABLE, OPTIMIZE TABLE, ANALYZE TABLE, CHECK TABLE, CREATE SERVER, ALTER SERVER, DROP SERVER, CACHE INDEX, LOAD INDEX INTO CACHE, FLUSH, or RESET when gtid_next is set to any value other than AUTOMATIC; in such cases, the statement fails with an error. Such statements are not disallowed in MySQL 5.7.2 and later. (Bug #16062608, Bug #16715809, Bug #69045) (Bug #16062608)

  • gtid_owned

    System VariableNamegtid_owned
    Variable ScopeGlobal, Session
    Dynamic VariableNo
    Permitted ValuesTypestring

    This read-only variable holds a list whose contents depend on its scope. When used with session scope, the list holds all GTIDs that are owned by this client; when used with global scope, it holds a list of all GTIDs along with their owners.

  • gtid_purged

    System VariableNamegtid_purged
    Variable ScopeGlobal
    Dynamic VariableYes
    Permitted ValuesTypestring

    The set of all transactions that have been purged from the binary log. This is a subset of the set of transactions in gtid_executed. The value of this variable is a GTID set, see GTID Sets for more information.

    When the server starts, the global value of gtid_purged is initialized to a set of GTIDs. See binlog_gtid_simple_recovery for more information on how binary logs are iterated to populate gtid_purged. Issuing RESET MASTER causes the value of this variable to be reset to an empty string.

    It is possible to update the value of this variable, but only when gtid_executed is the empty string, and therefore gtid_purged is the empty string. This can occur either when replication has not been started previously, or when replication was not previously using GTIDs. Prior to MySQL 5.7.6, this variable was settable only when gtid_mode=ON. In MySQL 5.7.6 and later, this variable is settable regardless of the value of gtid_mode.

    If all existing binary logs were generated using MySQL 5.7.6 or later, after issuing a SET gtid_purged statement, binlog_gtid_simple_recovery=TRUE (the default setting in MySQL 5.7.7 and later) can safely be used. If binary logs from MySQL 5.7.7 or earlier exist, there is a chance that gtid_purged may be computed incorrectly. See binlog_gtid_simple_recovery for more information. If you are using MySQL 5.7.7 or earlier, after issuing a SET gtid_purged statement note down the current binary log file name, which can be checked using SHOW MASTER STATUS. If the server is restarted before this file has been purged, then you should use binlog_gtid_simple_recovery=FALSE to avoid gtid_purged or gtid_executed being computed incorrectly.

  • simplified_binlog_gtid_recovery

    Introduced5.7.5
    Deprecated5.7.6
    Command-Line Format--simplified-binlog-gtid-recovery
    System VariableNamesimplified_binlog_gtid_recovery
    Variable ScopeGlobal
    Dynamic VariableNo
    Permitted ValuesTypeboolean
    DefaultFALSE

    This option is deprecated and will be removed in a future MySQL release. Use the renamed binlog_gtid_simple_recovery to control how MySQL iterates through binary log files after a crash.

18.1.7 Common Replication Administration Tasks

Once replication has been started it executes without requiring much regular administration. This section describes how to check the status of replication and how to pause a slave.

18.1.7.1 Checking Replication Status

The most common task when managing a replication process is to ensure that replication is taking place and that there have been no errors between the slave and the master. The primary statement for this is SHOW SLAVE STATUS, which you must execute on each slave:

mysql> SHOW SLAVE STATUS\G
*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: master1
                  Master_User: root
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: mysql-bin.000004
          Read_Master_Log_Pos: 931
               Relay_Log_File: slave1-relay-bin.000056
                Relay_Log_Pos: 950
        Relay_Master_Log_File: mysql-bin.000004
             Slave_IO_Running: Yes
            Slave_SQL_Running: Yes
              Replicate_Do_DB:
          Replicate_Ignore_DB:
           Replicate_Do_Table:
       Replicate_Ignore_Table:
      Replicate_Wild_Do_Table:
  Replicate_Wild_Ignore_Table:
                   Last_Errno: 0
                   Last_Error:
                 Skip_Counter: 0
          Exec_Master_Log_Pos: 931
              Relay_Log_Space: 1365
              Until_Condition: None
               Until_Log_File:
                Until_Log_Pos: 0
           Master_SSL_Allowed: No
           Master_SSL_CA_File:
           Master_SSL_CA_Path:
              Master_SSL_Cert:
            Master_SSL_Cipher:
               Master_SSL_Key:
        Seconds_Behind_Master: 0
Master_SSL_Verify_Server_Cert: No
                Last_IO_Errno: 0
                Last_IO_Error:
               Last_SQL_Errno: 0
               Last_SQL_Error:
  Replicate_Ignore_Server_Ids: 0

The key fields from the status report to examine are:

  • Slave_IO_State: The current status of the slave. See Section 9.14.5, “Replication Slave I/O Thread States”, and Section 9.14.6, “Replication Slave SQL Thread States”, for more information.

  • Slave_IO_Running: Whether the I/O thread for reading the master's binary log is running. Normally, you want this to be Yes unless you have not yet started replication or have explicitly stopped it with STOP SLAVE.

  • Slave_SQL_Running: Whether the SQL thread for executing events in the relay log is running. As with the I/O thread, this should normally be Yes.

  • Last_IO_Error, Last_SQL_Error: The last errors registered by the I/O and SQL threads when processing the relay log. Ideally these should be blank, indicating no errors.

  • Seconds_Behind_Master: The number of seconds that the slave SQL thread is behind processing the master binary log. A high number (or an increasing one) can indicate that the slave is unable to handle events from the master in a timely fashion.

    A value of 0 for Seconds_Behind_Master can usually be interpreted as meaning that the slave has caught up with the master, but there are some cases where this is not strictly true. For example, this can occur if the network connection between master and slave is broken but the slave I/O thread has not yet noticed this—that is, slave_net_timeout has not yet elapsed.

    It is also possible that transient values for Seconds_Behind_Master may not reflect the situation accurately. When the slave SQL thread has caught up on I/O, Seconds_Behind_Master displays 0; but when the slave I/O thread is still queuing up a new event, Seconds_Behind_Master may show a large value until the SQL thread finishes executing the new event. This is especially likely when the events have old timestamps; in such cases, if you execute SHOW SLAVE STATUS several times in a relatively short period, you may see this value change back and forth repeatedly between 0 and a relatively large value.

Several pairs of fields provide information about the progress of the slave in reading events from the master binary log and processing them in the relay log:

  • (Master_Log_file, Read_Master_Log_Pos): Coordinates in the master binary log indicating how far the slave I/O thread has read events from that log.

  • (Relay_Master_Log_File, Exec_Master_Log_Pos): Coordinates in the master binary log indicating how far the slave SQL thread has executed events received from that log.

  • (Relay_Log_File, Relay_Log_Pos): Coordinates in the slave relay log indicating how far the slave SQL thread has executed the relay log. These correspond to the preceding coordinates, but are expressed in slave relay log coordinates rather than master binary log coordinates.

On the master, you can check the status of connected slaves using SHOW PROCESSLIST to examine the list of running processes. Slave connections have Binlog Dump in the Command field:

mysql> SHOW PROCESSLIST \G;
*************************** 4. row ***************************
     Id: 10
   User: root
   Host: slave1:58371
     db: NULL
Command: Binlog Dump
   Time: 777
  State: Has sent all binlog to slave; waiting for binlog to be updated
   Info: NULL

Because it is the slave that drives the replication process, very little information is available in this report.

For slaves that were started with the --report-host option and are connected to the master, the SHOW SLAVE HOSTS statement on the master shows basic information about the slaves. The output includes the ID of the slave server, the value of the --report-host option, the connecting port, and master ID:

mysql> SHOW SLAVE HOSTS;
+-----------+--------+------+-------------------+-----------+
| Server_id | Host   | Port | Rpl_recovery_rank | Master_id |
+-----------+--------+------+-------------------+-----------+
|        10 | slave1 | 3306 |                 0 |         1 |
+-----------+--------+------+-------------------+-----------+
1 row in set (0.00 sec)

18.1.7.2 Pausing Replication on the Slave

You can stop and start replication on the slave using the STOP SLAVE and START SLAVE statements.

To stop processing of the binary log from the master, use STOP SLAVE:

mysql> STOP SLAVE;

When replication is stopped, the slave I/O thread stops reading events from the master binary log and writing them to the relay log, and the SQL thread stops reading events from the relay log and executing them. You can pause the I/O or SQL thread individually by specifying the thread type:

mysql> STOP SLAVE IO_THREAD;
mysql> STOP SLAVE SQL_THREAD;

To start execution again, use the START SLAVE statement:

mysql> START SLAVE;

To start a particular thread, specify the thread type:

mysql> START SLAVE IO_THREAD;
mysql> START SLAVE SQL_THREAD;

For a slave that performs updates only by processing events from the master, stopping only the SQL thread can be useful if you want to perform a backup or other task. The I/O thread will continue to read events from the master but they are not executed. This makes it easier for the slave to catch up when you restart the SQL thread.

Stopping only the I/O thread enables the events in the relay log to be executed by the SQL thread up to the point where the relay log ends. This can be useful when you want to pause execution to catch up with events already received from the master, when you want to perform administration on the slave but also ensure that it has processed all updates to a specific point. This method can also be used to pause event receipt on the slave while you conduct administration on the master. Stopping the I/O thread but permitting the SQL thread to run helps ensure that there is not a massive backlog of events to be executed when replication is started again.

18.2 Replication Implementation

Replication is based on the master server keeping track of all changes to its databases (updates, deletes, and so on) in its binary log. The binary log serves as a written record of all events that modify database structure or content (data) from the moment the server was started. Typically, SELECT statements are not recorded because they modify neither database structure nor content.

Each slave that connects to the master requests a copy of the binary log. That is, it pulls the data from the master, rather than the master pushing the data to the slave. The slave also executes the events from the binary log that it receives. This has the effect of repeating the original changes just as they were made on the master. Tables are created or their structure modified, and data is inserted, deleted, and updated according to the changes that were originally made on the master.

Because each slave is independent, the replaying of the changes from the master's binary log occurs independently on each slave that is connected to the master. In addition, because each slave receives a copy of the binary log only by requesting it from the master, the slave is able to read and update the copy of the database at its own pace and can start and stop the replication process at will without affecting the ability to update to the latest database status on either the master or slave side.

For more information on the specifics of the replication implementation, see Section 18.2.2, “Replication Implementation Details”.

Masters and slaves report their status in respect of the replication process regularly so that you can monitor them. See Section 9.14, “Examining Thread Information”, for descriptions of all replicated-related states.

The master binary log is written to a local relay log on the slave before it is processed. The slave also records information about the current position with the master's binary log and the local relay log. See Section 18.2.4, “Replication Relay and Status Logs”.

Database changes are filtered on the slave according to a set of rules that are applied according to the various configuration options and variables that control event evaluation. For details on how these rules are applied, see Section 18.2.5, “How Servers Evaluate Replication Filtering Rules”.

18.2.1 Replication Formats

Replication works because events written to the binary log are read from the master and then processed on the slave. The events are recorded within the binary log in different formats according to the type of event. The different replication formats used correspond to the binary logging format used when the events were recorded in the master's binary log. The correlation between binary logging formats and the terms used during replication are:

  • When using statement-based binary logging, the master writes SQL statements to the binary log. Replication of the master to the slave works by executing the SQL statements on the slave. This is called statement-based replication (often abbreviated as SBR), which corresponds to the standard MySQL statement-based binary logging format. Replication capabilities in MySQL version 5.1.4 and earlier used this format exclusively.

  • When using row-based logging, the master writes events to the binary log that indicate how individual table rows are changed. Replication of the master to the slave works by copying the events representing the changes to the table rows to the slave. This is called row-based replication (often abbreviated as RBR).

  • You can also configure MySQL to use a mix of both statement-based and row-based logging, depending on which is most appropriate for the change to be logged. This is called mixed-format logging. When using mixed-format logging, a statement-based log is used by default. Depending on certain statements, and also the storage engine being used, the log is automatically switched to row-based in particular cases. Replication using the mixed format is often referred to as mixed-based replication or mixed-format replication. For more information, see Section 6.4.4.3, “Mixed Binary Logging Format”.

Prior to MySQL 5.7.7, statement-based format was the default. In MySQL 5.7.7 and later, row-based format is the default.

NDB Cluster.  The default binary logging format in MySQL NDB Cluster 7.5 is MIXED. You should note that MySQL Cluster Replication always uses row-based replication, and that the NDB storage engine is incompatible with statement-based replication. See Section 20.6.2, “General Requirements for NDB Cluster Replication”, for more information.

When using MIXED format, the binary logging format is determined in part by the storage engine being used and the statement being executed. For more information on mixed-format logging and the rules governing the support of different logging formats, see Section 6.4.4.3, “Mixed Binary Logging Format”.

The logging format in a running MySQL server is controlled by setting the binlog_format server system variable. This variable can be set with session or global scope. The rules governing when and how the new setting takes effect are the same as for other MySQL server system variables—setting the variable for the current session lasts only until the end of that session, and the change is not visible to other sessions; setting the variable globally requires a restart of the server to take effect. For more information, see Section 14.7.4.1, “SET Syntax for Variable Assignment”.

There are conditions under which you cannot change the binary logging format at runtime or doing so causes replication to fail. See Section 6.4.4.2, “Setting The Binary Log Format”.

You must have the SUPER privilege to set either the global or session binlog_format value.

The statement-based and row-based replication formats have different issues and limitations. For a comparison of their relative advantages and disadvantages, see Section 18.2.1.1, “Advantages and Disadvantages of Statement-Based and Row-Based Replication”.

With statement-based replication, you may encounter issues with replicating stored routines or triggers. You can avoid these issues by using row-based replication instead. For more information, see Section 22.7, “Binary Logging of Stored Programs”.

18.2.1.1 Advantages and Disadvantages of Statement-Based and Row-Based Replication

Each binary logging format has advantages and disadvantages. For most users, the mixed replication format should provide the best combination of data integrity and performance. If, however, you want to take advantage of the features specific to the statement-based or row-based replication format when performing certain tasks, you can use the information in this section, which provides a summary of their relative advantages and disadvantages, to determine which is best for your needs.

Advantages of statement-based replication
  • Proven technology.

  • Less data written to log files. When updates or deletes affect many rows, this results in much less storage space required for log files. This also means that taking and restoring from backups can be accomplished more quickly.

  • Log files contain all statements that made any changes, so they can be used to audit the database.

Disadvantages of statement-based replication
  • Statements that are unsafe for SBR.  Not all statements which modify data (such as INSERT DELETE, UPDATE, and REPLACE statements) can be replicated using statement-based replication. Any nondeterministic behavior is difficult to replicate when using statement-based replication. Examples of such Data Modification Language (DML) statements include the following:

    Statements that cannot be replicated correctly using statement-based replication are logged with a warning like the one shown here:

    [Warning] Statement is not safe to log in statement format.
    

    A similar warning is also issued to the client in such cases. The client can display it using SHOW WARNINGS.

  • INSERT ... SELECT requires a greater number of row-level locks than with row-based replication.

  • UPDATE statements that require a table scan (because no index is used in the WHERE clause) must lock a greater number of rows than with row-based replication.

  • For InnoDB: An INSERT statement that uses AUTO_INCREMENT blocks other nonconflicting INSERT statements.

  • For complex statements, the statement must be evaluated and executed on the slave before the rows are updated or inserted. With row-based replication, the slave only has to modify the affected rows, not execute the full statement.

  • If there is an error in evaluation on the slave, particularly when executing complex statements, statement-based replication may slowly increase the margin of error across the affected rows over time. See Section 18.4.1.28, “Slave Errors During Replication”.

  • Stored functions execute with the same NOW() value as the calling statement. However, this is not true of stored procedures.

  • Deterministic UDFs must be applied on the slaves.

  • Table definitions must be (nearly) identical on master and slave. See Section 18.4.1.10, “Replication with Differing Table Definitions on Master and Slave”, for more information.

Advantages of row-based replication
  • All changes can be replicated. This is the safest form of replication.

    Note

    Statements that update the information in the mysql database—such as GRANT, REVOKE and the manipulation of triggers, stored routines (including stored procedures), and views—are all replicated to slaves using statement-based replication.

    For statements such as CREATE TABLE ... SELECT, a CREATE statement is generated from the table definition and replicated using statement-based format, while the row insertions are replicated using row-based format.

  • Fewer row locks are required on the master, which thus achieves higher concurrency, for the following types of statements:

  • Fewer row locks are required on the slave for any INSERT, UPDATE, or DELETE statement.

Disadvantages of row-based replication
  • RBR can generate more data that must be logged. To replicate a DML statement (such as an UPDATE or DELETE statement), statement-based replication writes only the statement to the binary log. By contrast, row-based replication writes each changed row to the binary log. If the statement changes many rows, row-based replication may write significantly more data to the binary log; this is true even for statements that are rolled back. This also means that making and restoring a backup can require more time. In addition, the binary log is locked for a longer time to write the data, which may cause concurrency problems. Use binlog_row_image=minimal to reduce the disadvantage considerably.

  • Deterministic UDFs that generate large BLOB values take longer to replicate with row-based replication than with statement-based replication. This is because the BLOB column value is logged, rather than the statement generating the data.

  • You cannot see on the slave what statements were received from the master and executed. However, you can see what data was changed using mysqlbinlog with the options --base64-output=DECODE-ROWS and --verbose.

    Alternatively, use the binlog_rows_query_log_events variable, which if enabled adds a Rows_query event with the statement to mysqlbinlog output when the -vv option is used.

  • For tables using the MyISAM storage engine, a stronger lock is required on the slave for INSERT statements when applying them as row-based events to the binary log than when applying them as statements. This means that concurrent inserts on MyISAM tables are not supported when using row-based replication.

18.2.1.2 Usage of Row-Based Logging and Replication

MySQL uses statement-based logging (SBL), row-based logging (RBL) or mixed-format logging. The type of binary log used impacts the size and efficiency of logging.Therefore the choice between row-based replication (RBR) or statement-based replication (SBR) depends on your application and environment. This section describes known issues when using a row-based format log, and describes some best practices using it in replication.

For additional information, see Section 18.2.1, “Replication Formats”, and Section 18.2.1.1, “Advantages and Disadvantages of Statement-Based and Row-Based Replication”.

For information about issues specific to MySQL Cluster Replication (which depends on row-based replication), see Section 20.6.3, “Known Issues in NDB Cluster Replication”.

  • Row-based logging of temporary tables.  As noted in Section 18.4.1.24, “Replication and Temporary Tables”, temporary tables are not replicated when using row-based format. When using mixed format logging, safe statements involving temporary tables are logged using statement-based format. For more information, see Section 18.2.1.1, “Advantages and Disadvantages of Statement-Based and Row-Based Replication”.

    Temporary tables are not replicated when using row-based format because there is no need. In addition, because temporary tables can be read only from the thread which created them, there is seldom if ever any benefit obtained from replicating them, even when using statement-based format.

    In MySQL 5.7, you can switch from statement-based to row-based binary logging mode even when temporary tables have been created. However, while using the row-based format, the MySQL server cannot determine the logging mode that was in effect when a given temporary table was created. For this reason, the server in such cases logs a DROP TEMPORARY TABLE IF EXISTS statement for each temporary table that still exists for a given client session when that session ends. While this means that it is possible that an unnecessary DROP TEMPORARY TABLE statement might be logged in some cases, the statement is harmless, and does not cause an error even if the table does not exist, due to the presence of the IF EXISTS option.

    Nontransactional DML statements involving temporary tables are allowed when using binlog_format=ROW, as long as any nontransactional tables affected by the statements are temporary tables (Bug #14272672).

  • RBL and synchronization of nontransactional tables.  When many rows are affected, the set of changes is split into several events; when the statement commits, all of these events are written to the binary log. When executing on the slave, a table lock is taken on all tables involved, and then the rows are applied in batch mode. Depending on the engine used for the slave's copy of the table, this may or may not be effective.

  • Latency and binary log size.  RBL writes changes for each row to the binary log and so its size can increase quite rapidly. This can significantly increase the time required to make changes on the slave that match those on the master. You should be aware of the potential for this delay in your applications.

  • Reading the binary log.  mysqlbinlog displays row-based events in the binary log using the BINLOG statement (see Section 14.7.6.1, “BINLOG Syntax”). This statement displays an event as a base 64-encoded string, the meaning of which is not evident. When invoked with the --base64-output=DECODE-ROWS and --verbose options, mysqlbinlog formats the contents of the binary log to be human readable. When binary log events were written in row-based format and you want to read or recover from a replication or database failure you can use this command to read contents of the binary log. For more information, see Section 5.6.7.2, “mysqlbinlog Row Event Display”.

  • Binary log execution errors and slave_exec_mode.  Using slave_exec_mode=IDEMPOTENT is generally only useful with MySQL NDB Cluster replication, for which IDEMPOTENT is the default value. (See Section 20.6.10, “NDB Cluster Replication: Multi-Master and Circular Replication”). When slave_exec_mode is IDEMPOTENT, a failure to apply changes from RBL because the original row cannot be found does not trigger an error or cause replication to fail. This means that it is possible that updates are not applied on the slave, so that the master and slave are no longer synchronized. Latency issues and use of nontransactional tables with RBR when slave_exec_mode is IDEMPOTENT can cause the master and slave to diverge even further. For more information about slave_exec_mode, see Section 6.1.5, “Server System Variables”.

    For other scenarios, setting slave_exec_mode to STRICT is normally sufficient; this is the default value for storage engines other than NDB.

  • Lack of binary log checksums.  RBL does not use checksums, so network, disk, and other errors may not be identified when processing the binary log. To ensure that data is transmitted without network corruption use SSL for replication connections. The CHANGE MASTER TO statement has options to enable replication over SSL. See also Section 14.4.2.1, “CHANGE MASTER TO Syntax”, for general information about setting up MySQL with SSL.

  • Filtering based on server ID not supported.  In MySQL 5.7, you can filter based on server ID by using the IGNORE_SERVER_IDS option for the CHANGE MASTER TO statement. This option works with statement-based and row-based logging formats. Another method to filter out changes on some slaves is to use a WHERE clause that includes the relation @@server_id <> id_value clause with UPDATE and DELETE statements. For example, WHERE @@server_id <> 1. However, this does not work correctly with row-based logging. To use the server_id system variable for statement filtering, use statement-based logging.

  • Database-level replication options.  The effects of the --replicate-do-db, --replicate-ignore-db, and --replicate-rewrite-db options differ considerably depending on whether row-based or statement-based logging is used. Therefore, it is recommended to avoid database-level options and instead use table-level options such as --replicate-do-table and --replicate-ignore-table. For more information about these options and the impact replication format has on how they operate, see Section 18.1.6, “Replication and Binary Logging Options and Variables”.

  • RBL, nontransactional tables, and stopped slaves.  When using row-based logging, if the slave server is stopped while a slave thread is updating a nontransactional table, the slave database can reach an inconsistent state. For this reason, it is recommended that you use a transactional storage engine such as InnoDB for all tables replicated using the row-based format. Use of STOP SLAVE or STOP SLAVE SQL_THREAD prior to shutting down the slave MySQL server helps prevent issues from occurring, and is always recommended regardless of the logging format or storage engine you use.

18.2.1.3 Determination of Safe and Unsafe Statements in Binary Logging

The safeness of a statement in MySQL Replication, refers to whether the statement and its effects can be replicated correctly using statement-based format. If this is true of the statement, we refer to the statement as safe; otherwise, we refer to it as unsafe.

In general, a statement is safe if it deterministic, and unsafe if it is not. However, certain nondeterministic functions are not considered unsafe (see Nondeterministic functions not considered unsafe, later in this section). In addition, statements using results from floating-point math functions—which are hardware-dependent—are always considered unsafe (see Section 18.4.1.13, “Replication and Floating-Point Values”).

Handling of safe and unsafe statements.  A statement is treated differently depending on whether the statement is considered safe, and with respect to the binary logging format (that is, the current value of binlog_format).

  • When using row-based logging, no distinction is made in the treatment of safe and unsafe statements.

  • When using mixed-format logging, statements flagged as unsafe are logged using the row-based format; statements regarded as safe are logged using the statement-based format.

  • When using statement-based logging, statements flagged as being unsafe generate a warning to this effect. Safe statements are logged normally.

Each statement flagged as unsafe generates a warning. Formerly, if a large number of such statements were executed on the master, this could lead to excessively large error log files. To prevent this, MySQL 5.7 provides a warning suppression mechanism, which behaves as follows: Whenever the 50 most recent ER_BINLOG_UNSAFE_STATEMENT warnings have been generated more than 50 times in any 50-second period, warning suppression is enabled. When activated, this causes such warnings not to be written to the error log; instead, for each 50 warnings of this type, a note The last warning was repeated N times in last S seconds is written to the error log. This continues as long as the 50 most recent such warnings were issued in 50 seconds or less; once the rate has decreased below this threshold, the warnings are once again logged normally. Warning suppression has no effect on how the safety of statements for statement-based logging is determined, nor on how warnings are sent to the client. MySQL clients still receive one warning for each such statement.

For more information, see Section 18.2.1, “Replication Formats”.

Statements considered unsafe.  Statements with the following characteristics are considered unsafe:

For additional information, see Section 18.4.1, “Replication Features and Issues”.

18.2.2 Replication Implementation Details

MySQL replication capabilities are implemented using three threads, one on the master server and two on the slave:

  • Binlog dump thread.  The master creates a thread to send the binary log contents to a slave when the slave connects. This thread can be identified in the output of SHOW PROCESSLIST on the master as the Binlog Dump thread.

    The binary log dump thread acquires a lock on the master's binary log for reading each event that is to be sent to the slave. As soon as the event has been read, the lock is released, even before the event is sent to the slave.

  • Slave I/O thread.  When a START SLAVE statement is issued on a slave server, the slave creates an I/O thread, which connects to the master and asks it to send the updates recorded in its binary logs.

    The slave I/O thread reads the updates that the master's Binlog Dump thread sends (see previous item) and copies them to local files that comprise the slave's relay log.

    The state of this thread is shown as Slave_IO_running in the output of SHOW SLAVE STATUS or as Slave_running in the output of SHOW STATUS.

  • Slave SQL thread.  The slave creates an SQL thread to read the relay log that is written by the slave I/O thread and execute the events contained therein.

In the preceding description, there are three threads per master/slave connection. A master that has multiple slaves creates one binary log dump thread for each currently connected slave, and each slave has its own I/O and SQL threads.

A slave uses two threads to separate reading updates from the master and executing them into independent tasks. Thus, the task of reading statements is not slowed down if statement execution is slow. For example, if the slave server has not been running for a while, its I/O thread can quickly fetch all the binary log contents from the master when the slave starts, even if the SQL thread lags far behind. If the slave stops before the SQL thread has executed all the fetched statements, the I/O thread has at least fetched everything so that a safe copy of the statements is stored locally in the slave's relay logs, ready for execution the next time that the slave starts.

The SHOW PROCESSLIST statement provides information that tells you what is happening on the master and on the slave regarding replication. For information on master states, see Section 9.14.4, “Replication Master Thread States”. For slave states, see Section 9.14.5, “Replication Slave I/O Thread States”, and Section 9.14.6, “Replication Slave SQL Thread States”.

The following example illustrates how the three threads show up in the output from SHOW PROCESSLIST.

On the master server, the output from SHOW PROCESSLIST looks like this:

mysql> SHOW PROCESSLIST\G
*************************** 1. row ***************************
     Id: 2
   User: root
   Host: localhost:32931
     db: NULL
Command: Binlog Dump
   Time: 94
  State: Has sent all binlog to slave; waiting for binlog to
         be updated
   Info: NULL

Here, thread 2 is a Binlog Dump replication thread that services a connected slave. The State information indicates that all outstanding updates have been sent to the slave and that the master is waiting for more updates to occur. If you see no Binlog Dump threads on a master server, this means that replication is not running; that is, no slaves are currently connected.

On a slave server, the output from SHOW PROCESSLIST looks like this:

mysql> SHOW PROCESSLIST\G
*************************** 1. row ***************************
     Id: 10
   User: system user
   Host:
     db: NULL
Command: Connect
   Time: 11
  State: Waiting for master to send event
   Info: NULL
*************************** 2. row ***************************
     Id: 11
   User: system user
   Host:
     db: NULL
Command: Connect
   Time: 11
  State: Has read all relay log; waiting for the slave I/O
         thread to update it
   Info: NULL

The State information indicates that thread 10 is the I/O thread that is communicating with the master server, and thread 11 is the SQL thread that is processing the updates stored in the relay logs. At the time that SHOW PROCESSLIST was run, both threads were idle, waiting for further updates.

The value in the Time column can show how late the slave is compared to the master. See Section A.13, “MySQL 5.7 FAQ: Replication”. If sufficient time elapses on the master side without activity on the Binlog Dump thread, the master determines that the slave is no longer connected. As for any other client connection, the timeouts for this depend on the values of net_write_timeout and net_retry_count; for more information about these, see Section 6.1.5, “Server System Variables”.

The SHOW SLAVE STATUS statement provides additional information about replication processing on a slave server. See Section 18.1.7.1, “Checking Replication Status”.

18.2.3 Replication Channels

MySQL 5.7.6 introduces the concept of a replication channel, which represents the path of transactions flowing from a master to a slave. This section describes how channels can be used in a replication topology, and the impact they have on single-source replication.

To provide compatibity with previous versions, the MySQL server automatically creates on startup a default channel whose name is the empty string (""). This channel is always present; it cannot be created or destroyed by the user. If no other channels (having nonempty names) have been created, replication statements act on the default channel only, so that all replication statements from older slaves function as expected (see Section 18.2.3.2, “Compatibility with Previous Replication Statements”. Statements applying to replication channels as described in this section can be used only when there is at least one named channel.

A replication channel encompasses the path of transactions transmitted from a master to a slave. In multi-source replication a slave opens multiple channels, one per master, and each channel has its own relay log and applier (SQL) threads. Once transactions are received by a replication channel's receiver (I/O) thread, they are added to the channel's relay log file and passed through to an applier thread. This enables channels to function independently.

A replication channel is also associated with a host name and port. You can assign multiple channels to the same combination of host name and port; in MySQL 5.7, the maximum number of channels that can be added to one slave in a multi-source replication topology is 256. Each replication channel must have a unique (nonempty) name (see Section 18.2.3.4, “Replication Channel Naming Conventions”). Channels can be configured independently.

18.2.3.1 Commands for Operations on a Single Channel

To enable existing MySQL replication statements to act on individual replication channels, MySQL 5.7.6 introduces the FOR CHANNEL channel_name option for use with the following replication statements in managing a replication channel independently of other channels:

Similarly, an additional channel_name parameter is introduced for the following functions:

Beginning with MySQL 5.7.9, the following statements are disallowed for the group_replication_recovery channel.

18.2.3.2 Compatibility with Previous Replication Statements

When a replication slave has multiple channels and a FOR CHANNEL channel_name option is not specified, a valid statement generally acts on all available channels.

For example, the following statements behave as expected:

  • START SLAVE starts replication threads for all channels. (In MySQL 5.7.9 and later, this does not include the group_replication_recovery channel.)

  • STOP SLAVE stops replication threads for all the channels. (In MySQL 5.7.9 and later, this does not include the group_replication_recovery channel.)

  • SHOW SLAVE STATUS reports the status for all channels.

  • FLUSH RELAY LOGS flushes the relay logs for all channels.

  • RESET SLAVE resets all channels.

Warning

Use RESET SLAVE with caution as this statement deletes all existing channels, purges their relay log files, and recreates only the default channel.

Some replication statements cannot operate on all channels. In this case, error 1964 Multiple channels exist on the slave. Please provide channel name as an argument. is generated. The following statements and functions generate this error when used in a multi-source replication topology and a FOR CHANNEL channel_name option is not used to specify which channel to act on:

Note that a default channel always exists in a single source replication topology, where statements and functions behave as in previous versions of MySQL.

18.2.3.3 Startup Options and Replication Channels

This section describes startup options which are impacted by the addition of replication channels.

The following startup options must be configured correctly to use multi-source replication.

  • --relay-log-info-repository

    This must be set to TABLE. If this option is set to FILE, attempting to add more sources to a slave fails with ER_SLAVE_NEW_CHANNEL_WRONG_REPOSITORY.

  • --master-info-repository

    This must be set to TABLE. If this option is set to FILE, attempting to add more sources to a slave fails with ER_SLAVE_NEW_CHANNEL_WRONG_REPOSITORY.

The following startup options now affect all channels in a replication topology.

The values set for the following startup options apply on each channel; since these are mysqld startup options, they are applied on every channel.

  • --max-relay-log-size=size

    Maximum size of the individual relay log file for each channel; after reaching this limit, the file is rotated.

  • --relay-log-space-limit=size

    Upper limit for the total size of all relay logs combined, for each individual channel. For N channels, the combined size of these logs is limited to relay_log_space_limit * N.

  • --slave-parallel-workers=value

    Number of slave parallel workers per channel.

  • --slave-checkpoint-group

    Waiting time by an I/O thread for each source.

  • --relay-log-index=filename

    Base name for each channel's relay log index file. See Section 18.2.3.4, “Replication Channel Naming Conventions”.

  • --relay-log=filename

    Denotes the base name of each channel's relay log file. See Section 18.2.3.4, “Replication Channel Naming Conventions”.

  • --slave_net-timeout=N

    This value is set per channel, so that each channel waits for N seconds to check for a broken connection.

  • --slave-skip-counter=N

    This value is set per channel, so that each channel skips N events from its master.

18.2.3.4 Replication Channel Naming Conventions

This section describes how naming conventions are impacted by replication channels.

Each replication channel has a unique name which is a string with a maximum length of 64 characters and is case insensitive. Because channel names are used in slave tables, the character set used for these is always UTF-8. Although you are generally free to use any name for channels, the following names are reserved:

  • group_replication_applier

  • group_replication_recovery

The name you choose for a replication channel also influences the file names used by a multi-source replication slave. The relay log files and index files for each channel are named base_name-relay-bin-channel_name.0000x, where base_name is generally a host name (if not specified using --log-bin) and channel_name is the name of the channel logged to this file.

18.2.4 Replication Relay and Status Logs

During replication, a slave server creates several logs that hold the binary log events relayed from the master to the slave, and to record information about the current status and location within the relay log. There are three types of logs used in the process, listed here:

  • The master info log contains status and current configuration information for the slave's connection to the master. This log holds information on the master host name, login credentials, and coordinates indicating how far the slave has read from the master's binary log.

    This log can be written to the mysql.slave_master_info table instead of a file, by starting the slave with --master-info-repository=TABLE.

  • The relay log consists of the events read from the binary log of the master and written by the slave I/O thread. Events in the relay log are executed on the slave as part of the SQL thread.

  • The relay log info log holds status information about the execution point within the slave's relay log.

    This log can be written to the mysql.slave_relay_log_info table instead of a file by starting the slave with --relay-log-info-repository=TABLE.

In MySQL 5.7, setting relay_log_info_repository and master_info_repository to TABLE can improve resilience to unexpected halts (crash-safe replication). See Section 18.3.2, “Handling an Unexpected Halt of a Replication Slave”. When using this configuration, a warning is given if mysqld is unable to initialize the replication logging tables, but the slave is allowed to continue starting. This situation is most likely to occur when upgrading from a version of MySQL that does not support slave logging tables to one in which they are supported.

Important

Do not attempt to update or insert rows in the slave_master_info or slave_relay_log_info table manually. Doing so can cause undefined behavior, and is not supported.

Execution of any statement requiring a write lock on either or both of the slave_master_info and slave_relay_log_info tables is disallowed while replication is ongoing, while statements that perform only reads are permitted at any time.

18.2.4.1 The Slave Relay Log

The relay log, like the binary log, consists of a set of numbered files containing events that describe database changes, and an index file that contains the names of all used relay log files.

The term relay log file generally denotes an individual numbered file containing database events. The term relay log collectively denotes the set of numbered relay log files plus the index file.

Relay log files have the same format as binary log files and can be read using mysqlbinlog (see Section 5.6.7, “mysqlbinlog — Utility for Processing Binary Log Files”).

By default, relay log file names have the form host_name-relay-bin.nnnnnn in the data directory, where host_name is the name of the slave server host and nnnnnn is a sequence number. Successive relay log files are created using successive sequence numbers, beginning with 000001. The slave uses an index file to track the relay log files currently in use. The default relay log index file name is host_name-relay-bin.index in the data directory.

The default relay log file and relay log index file names can be overridden with, respectively, the --relay-log and --relay-log-index server options (see Section 18.1.6, “Replication and Binary Logging Options and Variables”).

If a slave uses the default host-based relay log file names, changing a slave's host name after replication has been set up can cause replication to fail with the errors Failed to open the relay log and Could not find target log during relay log initialization. This is a known issue (see Bug #2122). If you anticipate that a slave's host name might change in the future (for example, if networking is set up on the slave such that its host name can be modified using DHCP), you can avoid this issue entirely by using the --relay-log and --relay-log-index options to specify relay log file names explicitly when you initially set up the slave. This will make the names independent of server host name changes.

If you encounter the issue after replication has already begun, one way to work around it is to stop the slave server, prepend the contents of the old relay log index file to the new one, and then restart the slave. On a Unix system, this can be done as shown here:

shell> cat new_relay_log_name.index >> old_relay_log_name.index
shell> mv old_relay_log_name.index new_relay_log_name.index

A slave server creates a new relay log file under the following conditions:

The SQL thread automatically deletes each relay log file as soon as it has executed all events in the file and no longer needs it. There is no explicit mechanism for deleting relay logs because the SQL thread takes care of doing so. However, FLUSH LOGS rotates relay logs, which influences when the SQL thread deletes them.

18.2.4.2 Slave Status Logs

A replication slave server creates two logs. By default, these logs are files named master.info and relay-log.info and created in the data directory. The names and locations of these files can be changed by using the --master-info-file and --relay-log-info-file options, respectively. In MySQL 5.7, either or both of these logs can also be written to tables in the mysql database by starting the server with the appropriate option: use --master-info-repository to have the master info log written to the mysql.slave_master_info table, and use --relay-log-info-repository to have the relay log info log written to the mysql.slave_relay_log_info table. See Section 18.1.6, “Replication and Binary Logging Options and Variables”.

The two status logs contain information like that shown in the output of the SHOW SLAVE STATUS statement, which is discussed in Section 14.4.2, “SQL Statements for Controlling Slave Servers”. Because the status logs are stored on disk, they survive a slave server's shutdown. The next time the slave starts up, it reads the two logs to determine how far it has proceeded in reading binary logs from the master and in processing its own relay logs.

The master info log file or table should be protected because it contains the password for connecting to the master. See Section 7.1.2.3, “Passwords and Logging”.

The slave I/O thread updates the master info log. The following table shows the correspondence between the lines in the master.info file, the columns in the mysql.slave_master_info table, and the columns displayed by SHOW SLAVE STATUS.

Line in master.info Fileslave_master_info Table ColumnSHOW SLAVE STATUS ColumnDescription
1Number_of_lines[None]Number of lines in the file, or columns in the table
2Master_log_nameMaster_Log_FileThe name of the master binary log currently being read from the master
3Master_log_posRead_Master_Log_PosThe current position within the master binary log that have been read from the master
4HostMaster_HostThe host name of the master
5User_nameMaster_UserThe user name used to connect to the master
6User_passwordPassword (not shown by SHOW SLAVE STATUS)The password used to connect to the master
7PortMaster_PortThe network port used to connect to the master
8Connect_retryConnect_RetryThe period (in seconds) that the slave will wait before trying to reconnect to the master
9Enabled_sslMaster_SSL_AllowedIndicates whether the server supports SSL connections
10Ssl_caMaster_SSL_CA_FileThe file used for the Certificate Authority (CA) certificate
11Ssl_capathMaster_SSL_CA_PathThe path to the Certificate Authority (CA) certificates
12Ssl_certMaster_SSL_CertThe name of the SSL certificate file
13Ssl_cipherMaster_SSL_CipherThe list of possible ciphers used in the handshake for the SSL connection
14Ssl_keyMaster_SSL_KeyThe name of the SSL key file
15Ssl_verify_server_certMaster_SSL_Verify_Server_CertWhether to verify the server certificate
16Heartbeat[None]Interval between replication heartbeats, in seconds
17BindMaster_BindWhich of the slave's network interfaces should be used for connecting to the master
18Ignored_server_idsReplicate_Ignore_Server_IdsThe list of server IDs to be ignored. Note that for Ignored_server_ids the list of server IDs is preceded by the total number of server IDs to ignore.
19UuidMaster_UUIDThe master's unique ID
20Retry_countMaster_Retry_CountMaximum number of reconnection attempts permitted
21Ssl_crl[None]Path to an ssl certificate revocation list file
22Ssl_crl_path[None]Path to a directory containing ssl certificate revocation list files
23Enabled_auto_positionAuto_positionIf autopositioning is in use or not
24Channel_nameChannel_nameThe name of the replication channel

The slave SQL thread updates the relay log info log. In MySQL 5.7, the relay-log.info file includes a line count and a replication delay value. The following table shows the correspondence between the lines in the relay-log.info file, the columns in the mysql.slave_relay_log_info table, and the columns displayed by SHOW SLAVE STATUS.

Line in relay-log.infoslave_relay_log_info Table ColumnSHOW SLAVE STATUS ColumnDescription
1Number_of_lines[None]Number of lines in the file or columns in the table
2Relay_log_nameRelay_Log_FileThe name of the current relay log file
3Relay_log_posRelay_Log_PosThe current position within the relay log file; events up to this position have been executed on the slave database
4Master_log_nameRelay_Master_Log_FileThe name of the master binary log file from which the events in the relay log file were read
5Master_log_posExec_Master_Log_PosThe equivalent position within the master's binary log file of events that have already been executed
6Sql_delaySQL_DelayThe number of seconds that the slave must lag the master
7Number_of_workers[None]The number of slave worker threads for executing replication events (transactions) in parallel
8Id[None]ID used for internal purposes; currently this is always 1
9Channel_nameChannel_nameThe name of the replication channel

In older versions of MySQL (prior to MySQL 5.6), the relay-log.info file does not include a line count or a delay value (and the slave_relay_log_info table is not available).

LineStatus ColumnDescription
1Relay_Log_FileThe name of the current relay log file
2Relay_Log_PosThe current position within the relay log file; events up to this position have been executed on the slave database
3Relay_Master_Log_FileThe name of the master binary log file from which the events in the relay log file were read
4Exec_Master_Log_PosThe equivalent position within the master's binary log file of events that have already been executed
Note

If you downgrade a slave server to a version older than MySQL 5.6, the older server does not read the relay-log.info file correctly. To address this, modify the file in a text editor by deleting the initial line containing the number of lines.

The contents of the relay-log.info file and the states shown by the SHOW SLAVE STATUS statement might not match if the relay-log.info file has not been flushed to disk. Ideally, you should only view relay-log.info on a slave that is offline (that is, mysqld is not running). For a running system, you can use SHOW SLAVE STATUS, or query the slave_master_info and slave_relay_log_info tables if you are writing the status logs to tables.

When you back up the slave's data, you should back up these two status logs, along with the relay log files. The status logs are needed to resume replication after you restore the data from the slave. If you lose the relay logs but still have the relay log info log, you can check it to determine how far the SQL thread has executed in the master binary logs. Then you can use CHANGE MASTER TO with the MASTER_LOG_FILE and MASTER_LOG_POS options to tell the slave to re-read the binary logs from that point. Of course, this requires that the binary logs still exist on the master.

18.2.5 How Servers Evaluate Replication Filtering Rules

If a master server does not write a statement to its binary log, the statement is not replicated. If the server does log the statement, the statement is sent to all slaves and each slave determines whether to execute it or ignore it.

On the master, you can control which databases to log changes for by using the --binlog-do-db and --binlog-ignore-db options to control binary logging. For a description of the rules that servers use in evaluating these options, see Section 18.2.5.1, “Evaluation of Database-Level Replication and Binary Logging Options”. You should not use these options to control which databases and tables are replicated. Instead, use filtering on the slave to control the events that are executed on the slave.

On the slave side, decisions about whether to execute or ignore statements received from the master are made according to the --replicate-* options that the slave was started with. (See Section 18.1.6, “Replication and Binary Logging Options and Variables”.) In MySQL 5.7.3 and later, the filters governed by these options can also be set dynamically using the CHANGE REPLICATION FILTER statement. The rules governing such filters are the same whether they are created on startup using --replicate-* options or while the slave server is running by CHANGE REPLICATION FILTER.

In the simplest case, when there are no --replicate-* options, the slave executes all statements that it receives from the master. Otherwise, the result depends on the particular options given.

Database-level options (--replicate-do-db, --replicate-ignore-db) are checked first; see Section 18.2.5.1, “Evaluation of Database-Level Replication and Binary Logging Options”, for a description of this process. If no database-level options are used, option checking proceeds to any table-level options that may be in use (see Section 18.2.5.2, “Evaluation of Table-Level Replication Options”, for a discussion of these). If one or more database-level options are used but none are matched, the statement is not replicated.

For statements affecting databases only (that is, CREATE DATABASE, DROP DATABASE, and ALTER DATABASE), database-level options always take precedence over any --replicate-wild-do-table options. In other words, for such statements, --replicate-wild-do-table options are checked if and only if there are no database-level options that apply. This is a change in behavior from previous versions of MySQL, where the statement CREATE DATABASE dbx was not replicated if the slave had been started with --replicate-do-db=dbx --replicate-wild-do-table=db%.t1. (Bug #46110)

To make it easier to determine what effect an option set will have, it is recommended that you avoid mixing do and ignore options, or wildcard and nonwildcard options.

If any --replicate-rewrite-db options were specified, they are applied before the --replicate-* filtering rules are tested.

Note

In MySQL 5.7, all replication filtering options follow the same rules for case sensitivity that apply to names of databases and tables elsewhere in the MySQL server, including the effects of the lower_case_table_names system variable.

This is a change from previous versions of MySQL. (Bug #51639)

18.2.5.1 Evaluation of Database-Level Replication and Binary Logging Options

When evaluating replication options, the slave begins by checking to see whether there are any --replicate-do-db or --replicate-ignore-db options that apply. When using --binlog-do-db or --binlog-ignore-db, the process is similar, but the options are checked on the master.

With statement-based replication, the default database is checked for a match. With row-based replication, the database where data is to be changed is the database that is checked. Regardless of the binary logging format, checking of database-level options proceeds as shown in the following diagram.

Evaluation of Database-Level Filtering Rules in Replication

The steps involved are listed here:

  1. Are there any --replicate-do-db options?

    • Yes.  Do any of them match the database?

      • Yes.  Execute the statement and exit.

      • No.  Ignore the statement and exit.

    • No.  Continue to step 2.

  2. Are there any --replicate-ignore-db options?

    • Yes.  Do any of them match the database?

      • Yes.  Ignore the statement and exit.

      • No.  Continue to step 3.

    • No.  Continue to step 3.

  3. Proceed to checking the table-level replication options, if there are any. For a description of how these options are checked, see Section 18.2.5.2, “Evaluation of Table-Level Replication Options”.

    Important

    A statement that is still permitted at this stage is not yet actually executed. The statement is not executed until all table-level options (if any) have also been checked, and the outcome of that process permits execution of the statement.

For binary logging, the steps involved are listed here:

  1. Are there any --binlog-do-db or --binlog-ignore-db options?

    • Yes.  Continue to step 2.

    • No.  Log the statement and exit.

  2. Is there a default database (has any database been selected by USE)?

    • Yes.  Continue to step 3.

    • No.  Ignore the statement and exit.

  3. There is a default database. Are there any --binlog-do-db options?

    • Yes.  Do any of them match the database?

      • Yes.  Log the statement and exit.

      • No.  Ignore the statement and exit.

    • No.  Continue to step 4.

  4. Do any of the --binlog-ignore-db options match the database?

    • Yes.  Ignore the statement and exit.

    • No.  Log the statement and exit.

Important

For statement-based logging, an exception is made in the rules just given for the CREATE DATABASE, ALTER DATABASE, and DROP DATABASE statements. In those cases, the database being created, altered, or dropped replaces the default database when determining whether to log or ignore updates.

--binlog-do-db can sometimes mean ignore other databases. For example, when using statement-based logging, a server running with only --binlog-do-db=sales does not write to the binary log statements for which the default database differs from sales. When using row-based logging with the same option, the server logs only those updates that change data in sales.

18.2.5.2 Evaluation of Table-Level Replication Options

The slave checks for and evaluates table options only if either of the following two conditions is true:

First, as a preliminary condition, the slave checks whether statement-based replication is enabled. If so, and the statement occurs within a stored function, the slave executes the statement and exits. If row-based replication is enabled, the slave does not know whether a statement occurred within a stored function on the master, so this condition does not apply.

Note

For statement-based replication, replication events represent statements (all changes making up a given event are associated with a single SQL statement); for row-based replication, each event represents a change in a single table row (thus a single statement such as UPDATE mytable SET mycol = 1 may yield many row-based events). When viewed in terms of events, the process of checking table options is the same for both row-based and statement-based replication.

Having reached this point, if there are no table options, the slave simply executes all events. If there are any --replicate-do-table or --replicate-wild-do-table options, the event must match one of these if it is to be executed; otherwise, it is ignored. If there are any --replicate-ignore-table or --replicate-wild-ignore-table options, all events are executed except those that match any of these options. This process is illustrated in the following diagram.

Evaluation of Table-Level Filtering Rules in Replication

The following steps describe this evaluation in more detail:

  1. Are there any table options?

    • Yes.  Continue to step 2.

    • No.  Execute the event and exit.

  2. Are there any --replicate-do-table options?

    • Yes.  Does the table match any of them?

      • Yes.  Execute the event and exit.

      • No.  Continue to step 3.

    • No.  Continue to step 3.

  3. Are there any --replicate-ignore-table options?

    • Yes.  Does the table match any of them?

      • Yes.  Ignore the event and exit.

      • No.  Continue to step 4.

    • No.  Continue to step 4.

  4. Are there any --replicate-wild-do-table options?

    • Yes.  Does the table match any of them?

      • Yes.  Execute the event and exit.

      • No.  Continue to step 5.

    • No.  Continue to step 5.

  5. Are there any --replicate-wild-ignore-table options?

    • Yes.  Does the table match any of them?

      • Yes.  Ignore the event and exit.

      • No.  Continue to step 6.

    • No.  Continue to step 6.

  6. Are there any --replicate-do-table or --replicate-wild-do-table options?

    • Yes.  Ignore the event and exit.

    • No.  Execute the event and exit.

18.2.5.3 Replication Rule Application

This section provides additional explanation and examples of usage for different combinations of replication filtering options.

Some typical combinations of replication filter rule types are given in the following table:

Condition (Types of Options)Outcome
No --replicate-* options at all:The slave executes all events that it receives from the master.
--replicate-*-db options, but no table options:The slave accepts or ignores events using the database options. It executes all events permitted by those options because there are no table restrictions.
--replicate-*-table options, but no database options:All events are accepted at the database-checking stage because there are no database conditions. The slave executes or ignores events based solely on the table options.
A combination of database and table options:The slave accepts or ignores events using the database options. Then it evaluates all events permitted by those options according to the table options. This can sometimes lead to results that seem counterintuitive, and that may be different depending on whether you are using statement-based or row-based replication; see the text for an example.

A more complex example follows, in which we examine the outcomes for both statement-based and row-based settings.

Suppose that we have two tables mytbl1 in database db1 and mytbl2 in database db2 on the master, and the slave is running with the following options (and no other replication filtering options):

replicate-ignore-db = db1
replicate-do-table  = db2.tbl2

Now we execute the following statements on the master:

USE db1;
INSERT INTO db2.tbl2 VALUES (1);

The results on the slave vary considerably depending on the binary log format, and may not match initial expectations in either case.

Statement-based replication.  The USE statement causes db1 to be the default database. Thus the --replicate-ignore-db option matches, and the INSERT statement is ignored. The table options are not checked.

Row-based replication.  The default database has no effect on how the slave reads database options when using row-based replication. Thus, the USE statement makes no difference in how the --replicate-ignore-db option is handled: the database specified by this option does not match the database where the INSERT statement changes data, so the slave proceeds to check the table options. The table specified by --replicate-do-table matches the table to be updated, and the row is inserted.

18.3 Replication Solutions

Replication can be used in many different environments for a range of purposes. This section provides general notes and advice on using replication for specific solution types.

For information on using replication in a backup environment, including notes on the setup, backup procedure, and files to back up, see Section 18.3.1, “Using Replication for Backups”.

For advice and tips on using different storage engines on the master and slaves, see Section 18.3.3, “Using Replication with Different Master and Slave Storage Engines”.

Using replication as a scale-out solution requires some changes in the logic and operation of applications that use the solution. See Section 18.3.4, “Using Replication for Scale-Out”.

For performance or data distribution reasons, you may want to replicate different databases to different replication slaves. See Section 18.3.5, “Replicating Different Databases to Different Slaves”

As the number of replication slaves increases, the load on the master can increase and lead to reduced performance (because of the need to replicate the binary log to each slave). For tips on improving your replication performance, including using a single secondary server as a replication master, see Section 18.3.6, “Improving Replication Performance”.

For guidance on switching masters, or converting slaves into masters as part of an emergency failover solution, see Section 18.3.7, “Switching Masters During Failover”.

To secure your replication communication, you can encrypt the communication channel. For step-by-step instructions, see Section 18.3.8, “Setting Up Replication to Use Secure Connections”.

18.3.1 Using Replication for Backups

To use replication as a backup solution, replicate data from the master to a slave, and then back up the data slave. The slave can be paused and shut down without affecting the running operation of the master, so you can produce an effective snapshot of live data that would otherwise require the master to be shut down.

How you back up a database depends on its size and whether you are backing up only the data, or the data and the replication slave state so that you can rebuild the slave in the event of failure. There are therefore two choices:

Another backup strategy, which can be used for either master or slave servers, is to put the server in a read-only state. The backup is performed against the read-only server, which then is changed back to its usual read/write operational status. See Section 18.3.1.3, “Backing Up a Master or Slave by Making It Read Only”.

18.3.1.1 Backing Up a Slave Using mysqldump

Using mysqldump to create a copy of a database enables you to capture all of the data in the database in a format that enables the information to be imported into another instance of MySQL Server (see Section 5.5.4, “mysqldump — A Database Backup Program”). Because the format of the information is SQL statements, the file can easily be distributed and applied to running servers in the event that you need access to the data in an emergency. However, if the size of your data set is very large, mysqldump may be impractical.

When using mysqldump, you should stop replication on the slave before starting the dump process to ensure that the dump contains a consistent set of data:

  1. Stop the slave from processing requests. You can stop replication completely on the slave using mysqladmin:

    shell> mysqladmin stop-slave

    Alternatively, you can stop only the slave SQL thread to pause event execution:

    shell> mysql -e 'STOP SLAVE SQL_THREAD;'

    This enables the slave to continue to receive data change events from the master's binary log and store them in the relay logs using the I/O thread, but prevents the slave from executing these events and changing its data. Within busy replication environments, permitting the I/O thread to run during backup may speed up the catch-up process when you restart the slave SQL thread.

  2. Run mysqldump to dump your databases. You may either dump all databases or select databases to be dumped. For example, to dump all databases:

    shell> mysqldump --all-databases > fulldb.dump
  3. Once the dump has completed, start slave operations again:

    shell> mysqladmin start-slave

In the preceding example, you may want to add login credentials (user name, password) to the commands, and bundle the process up into a script that you can run automatically each day.

If you use this approach, make sure you monitor the slave replication process to ensure that the time taken to run the backup does not affect the slave's ability to keep up with events from the master. See Section 18.1.7.1, “Checking Replication Status”. If the slave is unable to keep up, you may want to add another slave and distribute the backup process. For an example of how to configure this scenario, see Section 18.3.5, “Replicating Different Databases to Different Slaves”.

18.3.1.2 Backing Up Raw Data from a Slave

To guarantee the integrity of the files that are copied, backing up the raw data files on your MySQL replication slave should take place while your slave server is shut down. If the MySQL server is still running, background tasks may still be updating the database files, particularly those involving storage engines with background processes such as InnoDB. With InnoDB, these problems should be resolved during crash recovery, but since the slave server can be shut down during the backup process without affecting the execution of the master it makes sense to take advantage of this capability.

To shut down the server and back up the files:

  1. Shut down the slave MySQL server:

    shell> mysqladmin shutdown
  2. Copy the data files. You can use any suitable copying or archive utility, including cp, tar or WinZip. For example, assuming that the data directory is located under the current directory, you can archive the entire directory as follows:

    shell> tar cf /tmp/dbbackup.tar ./data
  3. Start the MySQL server again. Under Unix:

    shell> mysqld_safe &

    Under Windows:

    C:\> "C:\Program Files\MySQL\MySQL Server 5.7\bin\mysqld"

Normally you should back up the entire data directory for the slave MySQL server. If you want to be able to restore the data and operate as a slave (for example, in the event of failure of the slave), then in addition to the slave's data, you should also back up the slave status files, the master info and relay log info repositories, and the relay log files. These files are needed to resume replication after you restore the slave's data.

If you lose the relay logs but still have the relay-log.info file, you can check it to determine how far the SQL thread has executed in the master binary logs. Then you can use CHANGE MASTER TO with the MASTER_LOG_FILE and MASTER_LOG_POS options to tell the slave to re-read the binary logs from that point. This requires that the binary logs still exist on the master server.

If your slave is replicating LOAD DATA INFILE statements, you should also back up any SQL_LOAD-* files that exist in the directory that the slave uses for this purpose. The slave needs these files to resume replication of any interrupted LOAD DATA INFILE operations. The location of this directory is the value of the --slave-load-tmpdir option. If the server was not started with that option, the directory location is the value of the tmpdir system variable.

18.3.1.3 Backing Up a Master or Slave by Making It Read Only

It is possible to back up either master or slave servers in a replication setup by acquiring a global read lock and manipulating the read_only system variable to change the read-only state of the server to be backed up:

  1. Make the server read-only, so that it processes only retrievals and blocks updates.

  2. Perform the backup.

  3. Change the server back to its normal read/write state.

Note

The instructions in this section place the server to be backed up in a state that is safe for backup methods that get the data from the server, such as mysqldump (see Section 5.5.4, “mysqldump — A Database Backup Program”). You should not attempt to use these instructions to make a binary backup by copying files directly because the server may still have modified data cached in memory and not flushed to disk.

The following instructions describe how to do this for a master server and for a slave server. For both scenarios discussed here, suppose that you have the following replication setup:

  • A master server M1

  • A slave server S1 that has M1 as its master

  • A client C1 connected to M1

  • A client C2 connected to S1

In either scenario, the statements to acquire the global read lock and manipulate the read_only variable are performed on the server to be backed up and do not propagate to any slaves of that server.

Scenario 1: Backup with a Read-Only Master

Put the master M1 in a read-only state by executing these statements on it:

mysql> FLUSH TABLES WITH READ LOCK;
mysql> SET GLOBAL read_only = ON;

While M1 is in a read-only state, the following properties are true:

  • Requests for updates sent by C1 to M1 will block because the server is in read-only mode.

  • Requests for query results sent by C1 to M1 will succeed.

  • Making a backup on M1 is safe.

  • Making a backup on S1 is not safe. This server is still running, and might be processing the binary log or update requests coming from client C2

While M1 is read only, perform the backup. For example, you can use mysqldump.

After the backup operation on M1 completes, restore M1 to its normal operational state by executing these statements:

mysql> SET GLOBAL read_only = OFF;
mysql> UNLOCK TABLES;

Although performing the backup on M1 is safe (as far as the backup is concerned), it is not optimal for performance because clients of M1 are blocked from executing updates.

This strategy applies to backing up a master server in a replication setup, but can also be used for a single server in a nonreplication setting.

Scenario 2: Backup with a Read-Only Slave

Put the slave S1 in a read-only state by executing these statements on it:

mysql> FLUSH TABLES WITH READ LOCK;
mysql> SET GLOBAL read_only = ON;

While S1 is in a read-only state, the following properties are true:

  • The master M1 will continue to operate, so making a backup on the master is not safe.

  • The slave S1 is stopped, so making a backup on the slave S1 is safe.

These properties provide the basis for a popular backup scenario: Having one slave busy performing a backup for a while is not a problem because it does not affect the entire network, and the system is still running during the backup. In particular, clients can still perform updates on the master server, which remains unaffected by backup activity on the slave.

While S1 is read only, perform the backup. For example, you can use mysqldump.

After the backup operation on S1 completes, restore S1 to its normal operational state by executing these statements:

mysql> SET GLOBAL read_only = OFF;
mysql> UNLOCK TABLES;

After the slave is restored to normal operation, it again synchronizes to the master by catching up with any outstanding updates from the binary log of the master.

18.3.2 Handling an Unexpected Halt of a Replication Slave

In order for replication to be resilient to unexpected halts of the server (sometimes described as crash-safe) it must be possible for the slave to recover its state before halting. This section describes the impact of an unexpected halt of a slave during replication and how to configure a slave for the best chance of recovery to continue replication.

After an unexpected halt of a slave, upon restart the I/O thread must recover the information about which transactions have been received, and the SQL thread must recover which transactions have been executed already. For information on the slave logs required for recovery, see Section 18.2.4, “Replication Relay and Status Logs”. The information required for recovery was traditionally stored in files, which had the risk of losing synchrony with the master depending at which stage of processing a transaction the slave halted at, or even corruption of the files themselves. In MySQL 5.7 you can instead use tables to store this information. These tables are created using InnoDB, and by using this transactional storage engine the information is always recoverable upon restart. To configure MySQL 5.7 to store the replication information in tables, set relay_log_info_repository and master_info_repository to TABLE. The server then stores information required for the recovery of the I/O thread in the mysql.slave_master_info table and information required for the recovery of the SQL thread in the mysql.slave_relay_log_info table.

Exactly how a replication slave recovers from an unexpected halt is influenced by the chosen method of replication, whether the slave is single-threaded or multi-threaded, the setting of variables such as relay_log_recovery, and whether features such as MASTER_AUTO_POSITION are being used.

The following table shows the impact of these different factors on how a single-threaded slave recovers from an unexpected halt.

Table 18.5 Factors Influencing Single-threaded Replication Slave Recovery

GTID

MASTER_AUTO_POSITION

relay_log_recovery

relay_log_info_repository

Crash type

Recovery guaranteed

Relay log impact

OFF

Any

1

TABLE

Any

Yes

Lost

OFF

Any

1

TABLE

Server

Yes

Lost

OFF

Any

1

Any

OS

No

Lost

OFF

Any

0

TABLE

Server

Yes

Remains

OFF

Any

0

TABLE

OS

No

Remains

ON

ON

Any

Any

Any

Yes

Lost

ON

OFF

0

TABLE

Server

Yes

Remains

ON

OFF

0

Any

OS

No

Remains


As the table shows, when using a single-threaded slave the following configurations are most resilient to unexpected halts:

The following table shows the impact of these different factors on how a multi-threaded slave recovers from an unexpected halt.

Table 18.6 Factors Influencing Multi-threaded Replication Slave Recovery

GTID

sync_relay_log

MASTER_AUTO_POSITION

relay_log_recovery

relay_log_info_repository

Crash type

Recovery guaranteed

Relay log impact

OFF

1

Any

1

TABLE

Any

Yes

Lost

OFF

>1

Any

1

TABLE

Server

Yes

Lost

OFF

>1

Any

1

Any

OS

No

Lost

OFF

1

Any

0

TABLE

Server

Yes

Remains

OFF

1

Any

0

TABLE

OS

No

Remains

ON

Any

ON

Any

Any

Any

Yes

Lost

ON

1

OFF

0

TABLE

Server

Yes

Remains

ON

1

OFF

0

Any

OS

No

Remains


As the table shows, when using a multi-threaded slave the following configurations are most resilient to unexpected halts:

It is important to note the impact of sync_relay_log=1, which requires a write of to the relay log per transaction. Although this setting is the most resilient to an unexpected halt, with at most one unwritten transaction being lost, it also has the potential to greatly increase the load on storage. Without sync_relay_log=1, the effect of an unexpected halt depends on how the relay log is handled by the operating system. Also note that when relay_log_recovery=0, the next time the slave is started after an unexpected halt the relay log is processed as part of recovery. After this process completes, the relay log is deleted.

An unexpected halt of a multi-threaded replication slave using the recommended file position based replication configuration above may result in a relay log with transaction inconsistencies (gaps in the sequence of transactions) caused by the unexpected halt. See Section 18.4.1.34, “Replication and Transaction Inconsistencies”. In MySQL 5.7.13 and later, if the relay log recovery process encounters such transaction inconsistencies they are filled and the recovery process continues automatically. In MySQL versions prior to MySQL 5.7.13, this process is not automatic and requires starting the server with relay_log_recovery=0, starting the slave with START SLAVE UNTIL SQL_AFTER_MTS_GAPS to fix any transaction inconsistencies and then restarting the slave with relay_log_recovery=1.

When you are using multi-source replication and relay_log_recovery=1, after restarting due to an unexpected halt all replication channels go through the relay log recovery process. Any inconsistencies found in the relay log due to an unexpected halt of a multi-threaded slave are filled.

18.3.3 Using Replication with Different Master and Slave Storage Engines

It does not matter for the replication process whether the source table on the master and the replicated table on the slave use different engine types. In fact, the default_storage_engine and storage_engine system variables are not replicated.

This provides a number of benefits in the replication process in that you can take advantage of different engine types for different replication scenarios. For example, in a typical scale-out scenario (see Section 18.3.4, “Using Replication for Scale-Out”), you want to use InnoDB tables on the master to take advantage of the transactional functionality, but use MyISAM on the slaves where transaction support is not required because the data is only read. When using replication in a data-logging environment you may want to use the Archive storage engine on the slave.

Configuring different engines on the master and slave depends on how you set up the initial replication process:

  • If you used mysqldump to create the database snapshot on your master, you could edit the dump file text to change the engine type used on each table.

    Another alternative for mysqldump is to disable engine types that you do not want to use on the slave before using the dump to build the data on the slave. For example, you can add the --skip-federated option on your slave to disable the FEDERATED engine. If a specific engine does not exist for a table to be created, MySQL will use the default engine type, usually MyISAM. (This requires that the NO_ENGINE_SUBSTITUTION SQL mode is not enabled.) If you want to disable additional engines in this way, you may want to consider building a special binary to be used on the slave that only supports the engines you want.

  • If you are using raw data files (a binary backup) to set up the slave, you will be unable to change the initial table format. Instead, use ALTER TABLE to change the table types after the slave has been started.

  • For new master/slave replication setups where there are currently no tables on the master, avoid specifying the engine type when creating new tables.

If you are already running a replication solution and want to convert your existing tables to another engine type, follow these steps:

  1. Stop the slave from running replication updates:

    mysql> STOP SLAVE;
    

    This will enable you to change engine types without interruptions.

  2. Execute an ALTER TABLE ... ENGINE='engine_type' for each table to be changed.

  3. Start the slave replication process again:

    mysql> START SLAVE;
    

Although the default_storage_engine variable is not replicated, be aware that CREATE TABLE and ALTER TABLE statements that include the engine specification will be correctly replicated to the slave. For example, if you have a CSV table and you execute:

mysql> ALTER TABLE csvtable Engine='MyISAM';

The above statement will be replicated to the slave and the engine type on the slave will be converted to MyISAM, even if you have previously changed the table type on the slave to an engine other than CSV. If you want to retain engine differences on the master and slave, you should be careful to use the default_storage_engine variable on the master when creating a new table. For example, instead of:

mysql> CREATE TABLE tablea (columna int) Engine=MyISAM;

Use this format:

mysql> SET default_storage_engine=MyISAM;
mysql> CREATE TABLE tablea (columna int);

When replicated, the default_storage_engine variable will be ignored, and the CREATE TABLE statement will execute on the slave using the slave's default engine.

18.3.4 Using Replication for Scale-Out

You can use replication as a scale-out solution; that is, where you want to split up the load of database queries across multiple database servers, within some reasonable limitations.

Because replication works from the distribution of one master to one or more slaves, using replication for scale-out works best in an environment where you have a high number of reads and low number of writes/updates. Most Web sites fit into this category, where users are browsing the Web site, reading articles, posts, or viewing products. Updates only occur during session management, or when making a purchase or adding a comment/message to a forum.

Replication in this situation enables you to distribute the reads over the replication slaves, while still enabling your web servers to communicate with the replication master when a write is required. You can see a sample replication layout for this scenario in Figure 18.1, “Using Replication to Improve Performance During Scale-Out”.

Figure 18.1 Using Replication to Improve Performance During Scale-Out

Using replication to improve performance during scale-out

If the part of your code that is responsible for database access has been properly abstracted/modularized, converting it to run with a replicated setup should be very smooth and easy. Change the implementation of your database access to send all writes to the master, and to send reads to either the master or a slave. If your code does not have this level of abstraction, setting up a replicated system gives you the opportunity and motivation to clean it up. Start by creating a wrapper library or module that implements the following functions:

  • safe_writer_connect()

  • safe_reader_connect()

  • safe_reader_statement()

  • safe_writer_statement()

safe_ in each function name means that the function takes care of handling all error conditions. You can use different names for the functions. The important thing is to have a unified interface for connecting for reads, connecting for writes, doing a read, and doing a write.

Then convert your client code to use the wrapper library. This may be a painful and scary process at first, but it pays off in the long run. All applications that use the approach just described are able to take advantage of a master/slave configuration, even one involving multiple slaves. The code is much easier to maintain, and adding troubleshooting options is trivial. You need modify only one or two functions; for example, to log how long each statement took, or which statement among those issued gave you an error.

If you have written a lot of code, you may want to automate the conversion task by using the replace utility that comes with standard MySQL distributions, or write your own conversion script. Ideally, your code uses consistent programming style conventions. If not, then you are probably better off rewriting it anyway, or at least going through and manually regularizing it to use a consistent style.

18.3.5 Replicating Different Databases to Different Slaves

There may be situations where you have a single master and want to replicate different databases to different slaves. For example, you may want to distribute different sales data to different departments to help spread the load during data analysis. A sample of this layout is shown in Figure 18.2, “Using Replication to Replicate Databases to Separate Replication Slaves”.

Figure 18.2 Using Replication to Replicate Databases to Separate Replication Slaves

Using replication to replicate databases to separate replication slaves

You can achieve this separation by configuring the master and slaves as normal, and then limiting the binary log statements that each slave processes by using the --replicate-wild-do-table configuration option on each slave.

Important

You should not use --replicate-do-db for this purpose when using statement-based replication, since statement-based replication causes this option's affects to vary according to the database that is currently selected. This applies to mixed-format replication as well, since this enables some updates to be replicated using the statement-based format.

However, it should be safe to use --replicate-do-db for this purpose if you are using row-based replication only, since in this case the currently selected database has no effect on the option's operation.

For example, to support the separation as shown in Figure 18.2, “Using Replication to Replicate Databases to Separate Replication Slaves”, you should configure each replication slave as follows, before executing START SLAVE:

  • Replication slave 1 should use --replicate-wild-do-table=databaseA.%.

  • Replication slave 2 should use --replicate-wild-do-table=databaseB.%.

  • Replication slave 3 should use --replicate-wild-do-table=databaseC.%.

Each slave in this configuration receives the entire binary log from the master, but executes only those events from the binary log that apply to the databases and tables included by the --replicate-wild-do-table option in effect on that slave.

If you have data that must be synchronized to the slaves before replication starts, you have a number of choices:

  • Synchronize all the data to each slave, and delete the databases, tables, or both that you do not want to keep.

  • Use mysqldump to create a separate dump file for each database and load the appropriate dump file on each slave.

  • Use a raw data file dump and include only the specific files and databases that you need for each slave.

    Note

    This does not work with InnoDB databases unless you use innodb_file_per_table.

18.3.6 Improving Replication Performance

As the number of slaves connecting to a master increases, the load, although minimal, also increases, as each slave uses a client connection to the master. Also, as each slave must receive a full copy of the master binary log, the network load on the master may also increase and create a bottleneck.

If you are using a large number of slaves connected to one master, and that master is also busy processing requests (for example, as part of a scale-out solution), then you may want to improve the performance of the replication process.

One way to improve the performance of the replication process is to create a deeper replication structure that enables the master to replicate to only one slave, and for the remaining slaves to connect to this primary slave for their individual replication requirements. A sample of this structure is shown in Figure 18.3, “Using an Additional Replication Host to Improve Performance”.

Figure 18.3 Using an Additional Replication Host to Improve Performance

Using an additional replication host to improve performance

For this to work, you must configure the MySQL instances as follows:

  • Master 1 is the primary master where all changes and updates are written to the database. Binary logging should be enabled on this machine.

  • Master 2 is the slave to the Master 1 that provides the replication functionality to the remainder of the slaves in the replication structure. Master 2 is the only machine permitted to connect to Master 1. Master 2 also has binary logging enabled, and the --log-slave-updates option so that replication instructions from Master 1 are also written to Master 2's binary log so that they can then be replicated to the true slaves.

  • Slave 1, Slave 2, and Slave 3 act as slaves to Master 2, and replicate the information from Master 2, which actually consists of the upgrades logged on Master 1.

The above solution reduces the client load and the network interface load on the primary master, which should improve the overall performance of the primary master when used as a direct database solution.

If your slaves are having trouble keeping up with the replication process on the master, there are a number of options available:

  • If possible, put the relay logs and the data files on different physical drives. To do this, use the --relay-log option to specify the location of the relay log.

  • If the slaves are significantly slower than the master, you may want to divide up the responsibility for replicating different databases to different slaves. See Section 18.3.5, “Replicating Different Databases to Different Slaves”.

  • If your master makes use of transactions and you are not concerned about transaction support on your slaves, use MyISAM or another nontransactional engine on the slaves. See Section 18.3.3, “Using Replication with Different Master and Slave Storage Engines”.

  • If your slaves are not acting as masters, and you have a potential solution in place to ensure that you can bring up a master in the event of failure, then you can switch off --log-slave-updates. This prevents dumb slaves from also logging events they have executed into their own binary log.

18.3.7 Switching Masters During Failover

When using replication with GTIDs (see Section 18.1.3, “Replication with Global Transaction Identifiers”), you can provide failover between master and slaves in the event of a failure using mysqlfailover, which is provided by the MySQL Utilities; see mysqlfailover — Automatic replication health monitoring and failover, for more information. If you are not using GTIDs and therefore cannot use mysqlfailover, you must set up a master and one or more slaves; then, you need to write an application or script that monitors the master to check whether it is up, and instructs the slaves and applications to change to another master in case of failure. This section discusses some of the issues encountered when setting up failover in this way.

You can tell a slave to change to a new master using the CHANGE MASTER TO statement. The slave does not check whether the databases on the master are compatible with those on the slave; it simply begins reading and executing events from the specified coordinates in the new master's binary log. In a failover situation, all the servers in the group are typically executing the same events from the same binary log file, so changing the source of the events should not affect the structure or integrity of the database, provided that you exercise care in making the change.

Slaves should be run with the --log-bin option, and if not using GTIDs then they should also be run without --log-slave-updates. In this way, the slave is ready to become a master without restarting the slave