Chapter 16. Replication

Files relating to the mysql database.

The master.info file.

The master's binary log files.

Any relay log files.

Advantages of statement-based replication

Disadvantages of statement-based replication

Advantages of row-based replication

Disadvantages of row-based replication

Proven technology that has existed in MySQL since 3.23.

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.

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 DML (Data Modification Language) statements include the following:

Statements that cannot be replicated correctly using statement-based replication are logged with a warning like the one shown here:

090213 16:58:54 [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 16.4.1.26, “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 16.4.1.8, “Replication with Differing Table Definitions on Master and Slave”, for more information.

All changes can be replicated. This is the safest form of replication.

The mysql database is not replicated. The mysql database is instead seen as a node-specific database. Row-based replication is not supported on tables in this database. Instead, statements that would normally update this information—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.

The technology is the same as in most other database management systems; knowledge about other systems transfers to MySQL.

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.

RBR tends to 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 taking and restoring from 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.

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 examine the logs to see what statements were executed, nor can you 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.

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.

RBL, RBR, and temporary tables.  As noted in Section 16.4.1.22, “Replication and Temporary Tables”, temporary tables are not replicated when using row-based format. When mixed format is in effect, “safe” statements involving temporary tables are logged using statement-based format. For more information, see Section 16.1.2.1, “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 5.6, 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 NOT EXISTS option.

In MySQL 5.6.6 and earlier, the --disable-gtid-unsafe-statements option caused any nontransactional DML statement involving temporary tables to fail with an error when using row-based logging, in spite of the fact that they are not written to the binary log. In MySQL 5.6.7 and later, such statements 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. (This may or may not be effective, depending on the engine used for the slave's copy of the table.)

Latency and binary log size.  Because RBL writes changes for each row to the binary log, its size can increase quite rapidly. In a replication environment, 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 13.7.6.1, “BINLOG Syntax”). This statement displays an event in printable form, but 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 in a manner that is easily human readable. This is helpful when binary log events were written in row-based format if you want to read or recover from a replication or database failure using the contents of the binary log. For more information, see Section 4.6.8.2, “mysqlbinlog Row Event Display”.

Binary log execution errors and slave_exec_mode.  If 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 5.1.4, “Server System Variables”.

Lack of binary log checksums.  RBL uses no checksums. This means that network, disk, and other errors may not be identified when processing the binary log. To ensure that data is transmitted without network corruption, you may want to consider using SSL, which adds another layer of checksumming, for replication connections. The CHANGE MASTER TO statement has options to enable replication over SSL. See also Section 13.4.2.1, “CHANGE MASTER TO Syntax”, for general information about setting up MySQL with SSL.

Filtering based on server ID not supported.  A common practice is to filter out changes on some slaves by using a WHERE clause that includes the relation @@server_id <> id_value clause with UPDATE and DELETE statements, a simple example of such a clause being WHERE @@server_id <> 1. However, this does not work correctly with row-based logging. If you must use the server_id system variable for statement filtering, you must also use --binlog_format=STATEMENT.

In MySQL 5.6, you can do filtering based on server ID by using the IGNORE_SERVER_IDS option for the CHANGE MASTER TO statement. This option works with the statement-based and row-based logging formats.

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. Because of this, 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 that your choice of replication format has on how they operate, see Section 16.1.4, “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 may reaches 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 such issues from occurring, and is always recommended regardless of the logging format or storage engines employed.

No distinction is made in the treatment of safe and unsafe statements when the binary logging mode is ROW.

If the binary logging format is MIXED, statements flagged as unsafe are logged using the row-based format; statements regarded as safe are logged using the statement-based format.

If the binary logging format is STATEMENT, statements flagged as being unsafe generate a warning to this effect. (Safe statements are logged normally.)

Statements containing system functions that may return a different value on slave.  These functions include FOUND_ROWS(), GET_LOCK(), IS_FREE_LOCK(), IS_USED_LOCK(), LOAD_FILE(), MASTER_POS_WAIT(), RELEASE_LOCK(), PASSWORD(), ROW_COUNT(), SESSION_USER(), SLEEP(), SYSDATE(), SYSTEM_USER(), USER(), UUID(), and UUID_SHORT().

Nondeterministic functions not considered unsafe.  Although these functions are not deterministic, they are treated as safe for purposes of logging and replication: CONNECTION_ID(), CURDATE(), CURRENT_DATE(), CURRENT_TIME(), CURRENT_TIMESTAMP(), CURTIME(), LOCALTIME(), LOCALTIMESTAMP(), NOW(), UNIX_TIMESTAMP(), UTC_DATE(), UTC_TIME(), UTC_TIMESTAMP(), and LAST_INSERT_ID()

For more information, see Section 16.4.1.14, “Replication and System Functions”.

References to system variables.  Most system variables are not replicated correctly using the statement-based format. For exceptions, see Section 5.2.4.3, “Mixed Binary Logging Format”.

See Section 16.4.1.34, “Replication and Variables”.

UDFs.  Since we have no control over what a UDF does, we must assume that it is executing unsafe statements.

Updates a table having an AUTO_INCREMENT column.  This is unsafe because the order in which the rows are updated may differ on the master and the slave.

In addition, an INSERT into a table that has a composite primary key containing an AUTO_INCREMENT column that is not the first column of this composite key is unsafe.

For more information, see Section 16.4.1.1, “Replication and AUTO_INCREMENT”.

INSERT DELAYED statement.  This statement is considered unsafe because the insertion of the rows may interleave with concurrently executing statements.

INSERT ... ON DUPLICATE KEY UPDATE statements on tables with multiple primary or unique keys.  When executed against a table that contains more than one primary or unique key, this statement is considered unsafe, being sensitive to the order in which the storage engine checks the keys, which is not deterministic, and on which the choice of rows updated by the MySQL Server depends.

An INSERT ... ON DUPLICATE KEY UPDATE statement against a table having more than one unique or primary key is marked as unsafe for statement-based replication beginning with MySQL 5.6.6. (Bug #11765650, Bug #58637)

Updates using LIMIT.  The order in which rows are retrieved is not specified.

See Section 16.4.1.15, “Replication and LIMIT”.

Accesses or references log tables.  The contents of the system log table may differ between master and slave.

Nontransactional operations after transactional operations.  Within a transaction, allowing any nontransactional reads or writes to execute after any transactional reads or writes is considered unsafe.

For more information, see Section 16.4.1.30, “Replication and Transactions”.

Accesses or references self-logging tables.  All reads and writes to self-logging tables are considered unsafe. Within a transaction, any statement following a read or write to self-logging tables is also considered unsafe.

LOAD DATA INFILE statements.  Beginning with MySQL 5.6, LOAD DATA INFILE is considered unsafe, it causes a warning in statement-based mode, and a switch to row-based format when using mixed-format logging. See Section 16.4.1.16, “Replication and LOAD DATA INFILE”.

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.

When both the master and the slave use a nontransactional engine, but use different binary logging formats (for example, when the master has binlog_format=ROW and the slave has binlog_format=STATEMENT).

auto_increment_increment

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 gives rise to an error, and the actual value of the variable remains unchanged.

These two variables affect AUTO_INCREMENT column behavior as follows:

Should one or both of these variables be 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. In other words, the series is calculated like so:

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 greatest 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 confine the effects of these two variables to a single table, and thus they do not take the place of the sequences offered by some other database management systems; 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 16.4.1.1, “Replication and AUTO_INCREMENT”.

auto_increment_offset

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

slave_allow_batching

Whether or not batched updates are enabled on replication slaves.

slave_max_allowed_packet

In MySQL 5.6.6 and later, 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.

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-max-allowed-packet=bytes

In MySQL 5.6.6 and later, 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_rows_search_algorithms

When preparing batches of rows for row-based logging and replication using slave_allow_batching, the slave_rows_search_algorithms 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. This option 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:

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.

This variable was added in MySQL 5.6.6.

slave-rows-search-algorithms=list

When preparing batches of rows for row-based logging and replication using slave_allow_batching, 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:

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.

This option was added in MySQL 5.6.6.

--abort-slave-event-count

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.

This option is used internally by the MySQL test suite for replication testing and debugging. It is not intended for use in a production setting.

--disconnect-slave-event-count

This option is used internally by the MySQL test suite for replication testing and debugging.

--log-slave-updates

Normally, a slave does not log to its own binary log any updates that are received from a master server. This option tells the slave to log 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. Prior to MySQL 5.5, the server would not start when using the --log-slave-updates option without also starting the server with the --log-bin option, and would fail with an error; in MySQL 5.6, only a warning is generated. (Bug #44663) --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

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.

--log-warnings[=level]

This option causes a server to print 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/connection failure, and informs you as to how each slave thread started. This option is enabled by default; to disable it, use --skip-log-warnings. If the value is greater than 1, aborted connections are written to the error log, and access-denied errors for new connection attempts are written. See Section C.5.2.11, “Communication Errors and Aborted Connections”.

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

--master-info-file=file_name

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 16.2.2.2, “Slave Status Logs”.

--master-retry-count=count

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 as of MySQL 5.6.1 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

The size at which the server rotates relay log files automatically. For more information, see Section 16.2.2, “Replication Relay and Status Logs”. The default size is 1GB.

--read-only

Cause the slave to permit no updates except from slave threads or from users having the SUPER privilege. On a slave server, this can be useful to ensure that the slave accepts updates only from its master server and not from clients. This variable does not apply to TEMPORARY tables.

--relay-log=file_name

The basename for the relay log. The default basename is host_name-relay-bin. The server writes the file in the data directory unless the basename 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 basename.

Due to the manner in which MySQL parses server options, if you specify this option, you must supply a value; the default basename 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 4.2.3, “Specifying Program Options”.

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

Starting with MySQL 5.6.5, 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 in 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. Prior to MySQL 5.6.5, 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:

Beginning with MySQL 5.6.2, you can obtain the relay log filename (and path) from the relay_log_basename system variable.

--relay-log-index=file_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 slave server.

Due to the manner in which MySQL parses server options, if you specify this option, you must supply a value; the default basename 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 4.2.3, “Specifying Program Options”.

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

--relay-log-info-file=file_name

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 16.2.2.2, “Slave Status Logs”.

--relay-log-purge={0|1}

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.

--relay-log-recovery={0|1}

Enables automatic relay log recovery immediately following server startup, which means that the replication slave discards all unprocessed relay logs and retrieves them from the replication master. This should be used following a crash on the replication slave to ensure that no possibly corrupted relay logs are processed. The default value is 0 (disabled).

Prior to MySQL 5.6.6, if this option is enabled for a multi-threaded slave, and the slave fails with errors, you cannot execute CHANGE MASTER TO on that slave. In MySQL 5.6.6 or later, you can use START SLAVE UNTIL SQL_AFTER_MTS_GAPS to ensure that any gaps in the relay log are processed; after running this statement, you can then use CHANGE MASTER TO to fail this slave over to a new master. (Bug #13893363)

--relay-log-space-limit=size

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

The effects of this option depend on whether statement-based or row-based replication is in use.

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.

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 16.2.3, “How Servers Evaluate Replication Filtering Rules”.

--replicate-ignore-db=db_name

As with --replicate-do-db, the effects of this option depend on whether statement-based or row-based replication is in use.

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 16.2.3, “How Servers Evaluate Replication Filtering Rules”.

If you need cross-database updates to work, use --replicate-wild-ignore-table=db_name.% instead. See Section 16.2.3, “How Servers Evaluate Replication Filtering Rules”.

--replicate-do-table=db_name.tbl_name

Tells the slave SQL thread to restrict replication to the specified 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 16.2.3, “How Servers Evaluate Replication Filtering Rules”.

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

Tells 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 16.2.3, “How Servers Evaluate Replication Filtering Rules”.

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

Tells the slave to translate 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. This does not work for cross-database updates. 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.

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

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

Tells 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 16.2.3, “How Servers Evaluate Replication Filtering Rules”.

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

Tells the slave thread not to replicate a statement where 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 16.2.3, “How Servers Evaluate Replication Filtering Rules”.

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

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 that 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

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

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.

Prior to MySQL 5.6.5, the default value for this option was 3306. In MySQL 5.6.5 and later, the value shown is the port number actually used by the slave (Bug #13333431). This change also affects the default value displayed by SHOW SLAVE HOSTS.

--report-user=user_name

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

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=#

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 multithreading is not enabled.

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-group was added in MySQL 5.6.3.

--slave-checkpoint-period=#

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 multithreading is not enabled.

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-checkpoint-period was added in MySQL 5.6.3.

--slave-parallel-workers

Sets the number of slave worker threads for executing replication events (transactions) in parallel. Setting this variable to 0 (the default) disables parallel execution. The maximum is 1024.

When parallel execution is enabled, the slave SQL thread acts as the coordinator for the slave worker threads, among which transactions are distributed on a per-database basis. This means that a worker thread on the slave slave can process successive transactions on a given database without waiting for updates to other databases to complete. The current implementation of multi-threading on the slave assumes that the data is partitioned per database, and that updates within a given database occur in the same relative order as they do on the master, in order to work correctly. However, transactions do not need to be coordinated between any two databases.

Due to the fact that transactions on different databases can occur in a different order on the slave than on the master, 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 information about how to interpret binary logging information when using multi-threading on the slave, see Section 13.7.5.35, “SHOW SLAVE STATUS Syntax”. In addition, this means that START SLAVE UNTIL is not supported with a multi-threaded slave.

You should also note that, in MySQL 5.6.7 and later, enforcing foreign key relationships between tables in different databases causes multi-threaded slaves to use sequential rather than parallel mode, which can have a negative impact on performance. (Bug #14092635)

This option was added in MySQL 5.6.3.

--slave-pending-jobs-size-max=#

For multithreaded 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 multithreading 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.

This option was added in MySQL 5.6.3.

--skip-slave-start

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}

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=file_name

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-net-timeout=seconds

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. The default is 3600 seconds (one hour).

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

Normally, replication stops when an error occurs on the slave. This gives you the opportunity to resolve the inconsistency in the data manually. This option tells 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 C, 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.

Examples:

--slave-skip-errors=1062,1053
--slave-skip-errors=all

--slave-sql-verify-checksum={0|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.

This option was added in MySQL 5.6.2.

--master-host

--master-user

--master-password

--master-port

--master-connect-retry

--master-ssl

--master-ssl-ca

--master-ssl-capath

--master-ssl-cert

--master-ssl-cipher

--master-ssl-key

init_slave

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.

master_info_repository

This variable shows whether the slave logs master status and connection information to a file (master.info) or to a table (mysql.slave_master_info). This variable is read-only. Use the --master-info-repository server option to set the logging mode to FILE or TABLE.

This variable was added in MySQL 5.6.2.

relay_log

The name of the relay log file.

relay_log_basename

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

The relay_log_basename system variable was added in MySQL 5.6.2.

relay_log_index

The name of 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 slave server.

relay_log_info_file

The name of the file in which the slave records information about the relay logs. The default name is relay-log.info in the data directory.

relay_log_info_repository

This variable shows 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). This variable is read-only. Use the --relay-log-info-repository server option to set the logging mode to FILE or TABLE.

This variable was added in MySQL 5.6.2.

relay_log_recovery

Enables automatic relay log recovery immediately following server startup, which means that the replication slave discards all unprocessed relay logs and retrieves them from the replication master. This should be used following a crash on the replication slave to ensure that no possibly corrupted relay logs are processed. The default value is 0 (disabled). In MySQL 5.6.5 and earlier, it was possible to change this global variable dynamically; beginning with MySQL 5.6.6, it is read-only. (Bug #13840948) Regardless of the MySQL Server version, its value can be changed by starting the slave with the --relay-log-recovery option.

When relay_log_recovery is enabled and the slave has stopped due to errors encountered while running in multi-threaded mode, you cannot execute CHANGE MASTER TO if there are any gaps in the log. Beginning with MySQL 5.6.6, you should 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.

slave_checkpoint_group

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 multithreading is not enabled.

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_group was added in MySQL 5.6.3.

slave_checkpoint_period

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 multithreading is not enabled.

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_checkpoint_period was added in MySQL 5.6.3.

slave_compressed_protocol

Whether to use compression of the slave/master protocol if both the slave and the master support it.

slave_exec_mode

Controls whether IDEMPOTENT or STRICT mode is used in replication conflict resolution and error checking. IDEMPOTENT mode causes suppression of duplicate-key and no-key-found errors. This mode should be employed in multi-master replication, circular replication, and some other special replication scenarios. STRICT mode is the default, and is suitable for most other cases.

slave_load_tmpdir

The name of the directory where the slave creates temporary files for replicating LOAD DATA INFILE statements.

slave_net_timeout