cooperative_monitoring_locks can leave stale locks on a server if network breaks

If the network between MaxScale and MariaDB Server breaks, the server may not consider the connection broken. This can leave exclusive lock held for a long time, unable to be claimed by anyone. This issue can be mitigated with server tcp keepalive settings, but these settings affect all connections.

A more elegant solution is for the monitor to set session-level wait_timeout when connecting. This causes server to break the connection if it's idle for longer than the timeout. The value of the timeout must be set carefully, so as not to interfere with any monitor operations.