Semisynchronous Replication-opracowanie

Semisynchronous Replication
MySQL 5.6 supports an interface to semisynchronous replication in addition to the built-in
asynchronous replication. This section discusses what semisynchronous replication is and how it
works. The following sections cover the administrative interface to semisynchronous replication and
how to install, configure, and monitor it.
MySQL replication by default is asynchronous. The master writes events to its binary log but does not
know whether or when a slave has retrieved and processed them. With asynchronous replication, if
the master crashes, transactions that it has committed might not have been transmitted to any slave.
Consequently, failover from master to slave in this case may result in failover to a server that is missing
transactions relative to the master.
Semisynchronous replication can be used as an alternative to asynchronous replication:
• A slave indicates whether it is semisynchronous-capable when it connects to the master.
• If semisynchronous replication is enabled on the master side and there is at least one
semisynchronous slave, a thread that performs a transaction commit on the master blocks after
the commit is done and waits until at least one semisynchronous slave acknowledges that it has
received all events for the transaction, or until a timeout occurs.
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