To stop processing of the binary log from the source, use
mysql> STOP SLAVE;
When replication is stopped, the slave I/O thread stops reading events from the source's binary log and writing them to the relay log, and the SQL thread stops reading events from the relay log and executing them. You can pause the I/O or SQL thread individually by specifying the thread type:
mysql> STOP SLAVE IO_THREAD; mysql> STOP SLAVE SQL_THREAD;
To start execution again, use the
mysql> START SLAVE;
To start a particular thread, specify the thread type:
mysql> START SLAVE IO_THREAD; mysql> START SLAVE SQL_THREAD;
For a slave that performs updates only by processing events from the source, stopping only the SQL thread can be useful if you want to perform a backup or other task. The I/O thread will continue to read events from the source but they are not executed. This makes it easier for the slave to catch up when you restart the SQL thread.
Stopping only the I/O thread enables the events in the relay log to be executed by the SQL thread up to the point where the relay log ends. This can be useful when you want to pause execution to catch up with events already received from the source, when you want to perform administration on the slave but also ensure that it has processed all updates to a specific point. This method can also be used to pause event receipt on the slave while you conduct administration on the source. Stopping the I/O thread but permitting the SQL thread to run helps ensure that there is not a massive backlog of events to be executed when replication is started again.