MySQL 5.7 Release Notes
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_infotable 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_infotable 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 16.3.2, “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.