3.9.1 Semisynchronous Replication Administrative Interface

The administrative interface to semisynchronous replication has several components:

• Two plugins implement semisynchronous capability. There is one plugin for the source side and one for the replica side.

• System variables control plugin behavior. Some examples:

  • rpl_semi_sync_master_enabled

    Controls whether semisynchronous replication is enabled on the source. To enable or disable the plugin, set this variable to 1 or 0, respectively. The default is 0 (off).

  • rpl_semi_sync_master_timeout

    A value in milliseconds that controls how long the source waits on a commit for acknowledgment from a replica before timing out and reverting to asynchronous replication. The default value is 10000 (10 seconds).

  • rpl_semi_sync_slave_enabled

    Similar to rpl_semi_sync_master_enabled, but controls the replica plugin.

  All rpl_semi_sync_xxx system variables are described at Server System Variables.

• Status variables enable semisynchronous replication monitoring. Some examples:

  • Rpl_semi_sync_master_clients

    The number of semisynchronous replicas.

  • Rpl_semi_sync_master_status

    Whether semisynchronous replication currently is operational on the source. The value is 1 if the plugin has been enabled and a commit acknowledgment has not occurred. It is 0 if the plugin is not enabled or the source has fallen back to asynchronous replication due to commit acknowledgment timeout.

  • Rpl_semi_sync_master_no_tx

    The number of commits that were not acknowledged successfully by a replica.

  • Rpl_semi_sync_master_yes_tx

    The number of commits that were acknowledged successfully by a replica.

  • Rpl_semi_sync_slave_status

    Whether semisynchronous replication currently is operational on the replica. This is 1 if the plugin has been enabled and the replication I/O thread is running, 0 otherwise.

  All Rpl_semi_sync_xxx status variables are described at Server Status Variables.

The system and status variables are available only if the appropriate source or replica plugin has been installed with INSTALL PLUGIN.