The plugins for semisynchronous replication expose a number of
status variables that enable you to monitor their operation. To
check the current values of the status variables, use
mysql> SHOW STATUS LIKE 'Rpl_semi_sync%';
From MySQL 8.0.26, new versions of the source and replica
plugins are supplied, which replace the terms
“master” and “slave” with
“source” and “replica” in system
variables and status variables. If you install the new
rpl_semi_sync_replica plugins, the new system
variables and status variables are available but the old ones
are not. If you install the old
rpl_semi_sync_slave plugins, the old system
variables and status variables are available but the new ones
are not. You cannot have both the new and the old version of the
relevant plugin installed on an instance.
status variables are described at
Section 5.1.10, “Server Status Variables”. Some examples are:
The number of semisynchronous replicas that are connected to the source server.
Whether semisynchronous replication currently is operational on the source server. 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.
The number of commits that were not acknowledged successfully by a replica.
The number of commits that were acknowledged successfully by a replica.
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.
When the source switches between asynchronous or semisynchronous
replication due to commit-blocking timeout or a replica catching
up, it sets the value of the
status variable appropriately. Automatic fallback from
semisynchronous to asynchronous replication on the source means
that it is possible for the
system variable to have a value of 1 on the source side even
when semisynchronous replication is in fact not operational at
the moment. You can monitor the
status variable to determine whether the source currently is
using asynchronous or semisynchronous replication.