Check manual page of mysql.sessions
MySQL Database sessions
This check allows tracking of the session parameters for a MySQL database.
It reports how many sessions there are in total, how many of them are
active, and at what rate new sessions are generated.
It allows to set WARN and CRIT tresholds on any of these parameters.
The data is gathered from the show global status query.
The check generates one item per instance for the sessions connected to the MySQL daemon.