Monitoring read replication

After setting up replication, you should periodically monitor your replicas to ensure that they are in a healthy state. See the table below for the mysql variables that you should monitor.

All the variables mentioned in the table below for monitoring replication are present in the monitoring agent running on your database instance. You can monitor these variables using https://intelligence.rackspace.com and also set up alarms to be notified of the state of your replica. You can also monitor these variables by executing the ‘SHOW GLOBAL STATUS’ and ‘SHOW SLAVE STATUS’ commands.

Variables for Monitoring Read Replication

Variable	Description
Slave_running	This is a global status variable and its value can be ‘ON’ or ‘OFF’. If the value is ‘ON’ that means the replica is connected to the source DB instance and both SQL thread and IO thread are running. If the value is ‘OFF’, you look at Last_SQL_Errno and Last_SQL_Error for more error information.
Slave_IO_Running	This variable is a part of the Show Slave status and its value can be ‘Yes’, ‘No’, or ‘Connecting’. If the value is ‘No’, that means the replica I/O thread is not running and you can look at Last_IO_Errno and Last_IO_Error for more error information.
Slave_SQL_Running	This variable is a part of the Show Slave status and its value can be ‘Yes’ or ‘No’. It tells whether the replica’s SQL thread has started and is working well. If the value is ‘No’, you can look at Last_SQL_Errno and Last_SQL_Error for more error information.
Last_IO_Errno	Indicates the error number of the most recent thread that caused the I/O thread to stop.
Last_IO_Error	Indicates the error message of the most recent thread that caused the I/O thread to stop.
Last_SQL_Errno	Indicates the error number of the most recent thread that caused the MySQL thread to stop.
Last_SQL_Error	Indicates the error message of the most recent thread that caused the MySQL thread to stop.