How to verify if a slave running in MySQL 5.7
Most people know that you can use
SHOW SLAVE STATUS to verify if a slave is running in MySQL. Most people also know that you need to check both
Slave_IO_Running and
Slave_SQL_Running. https://gist.github.com/dtest/86db850f26f19d8c7bb81b95f6241f31#file-show-slave-status-sql A few years ago, I responded to a question on
dba.stackexchange.com on how to verify if a slave is running outside of
SHOW SLAVE STATUS. Prior to MySQL 5.7, you could get this information from
SHOW GLOBAL STATUS: https://gist.github.com/dtest/86db850f26f19d8c7bb81b95f6241f31#file-mysql-56-sql Keep in mind that certain versions of 5.1
might give false information if the
Slave_IO_Thread was not running. But if you upgrade to MySQL 5.7 and your application relies on anything other than
SHOW SLAVE STATUS output, it might be broken. In MySQL 5.7, you would get this: https://gist.github.com/dtest/86db850f26f19d8c7bb81b95f6241f31#file-without_56_compat-sql The reason is that
MySQL is moving away from the information_schema
GLOBAL_STATUS and
SESSION_STATUS tables in preference for performance_schema. The correct way to get the status of slave running in MySQL 5.7 outside of
SHOW SLAVE STATUS is to use the new replication-based performance_schema tables:
- IO Thread: performance_schema.replication_connection_status
- SQL Thread (single master):performance_schema.replication_applier_status
Conclusion
If your applications (monitoring or other) rely on checking that slaves are running by utilizing the information schema GLOBAL_STATUS table, upgrading to MySQL 5.7 will break it. You have a few choices:- Use SHOW SLAVE STATUS directly and parse the output of Slave_IO_Running and Slave_SQL_Running. This requires application changes.
- Use the new performance_schema replication tables performance_schema.replication_connection_status and performance_schema.replication_applier_status. This also requires an application change. And it should be noted that there are other tables for multi-master setups!
- Use the compatibility variable show_compatibility_56. This is dynamic and doesn't require application changes. However, this variable is immediately deprecated and will go away in a future release, so you will be required to update your application at some point anyway.
