check_mysql_threads

Nagios plugin for MySQL.

Checks the MySQL processlist for long running threads.

Threads which have been running for a long time could signal that something is very wrong within MySQL, such as hung queries wasting CPU cycles.

This could be caused by application contention, for example, when trying to acquire locks on the same rows.

However, long running threads could also be caused by DDL statements, such as running ALTER on large tables.

This plugin can be helpful in monitoring the overall health of an infrastructure, when combined with other standard checks.

For example, a webserver might not be responding to clients' requests.

In such situations, it's tempting to focus only on the webserver, to try and figure out what is wrong.

Although in fact, it might be MySQL who is causing the actual problem, because it can't keep up with SQL queries from the application.