Using Cooperative Locking for HA with MaxScale's MariaDB Monitor

MaxScale's MariaDB Monitor (mariadbmon) monitors MariaDB replication deployments.

When multiple MaxScale instances are used in a highly available deployment, MariaDB Monitor needs to ensure that only one MaxScale instance performs automatic failover operations at a given time. It does this by using cooperative locks on the back-end servers.

How MariaDB Monitor uses Cooperative Locks

When cooperative locking is enabled for MariaDB Monitor, it tries to acquire locks on the back-end servers with GET_LOCK() function. If a specific MaxScale instance is able to acquire the lock on a majority of servers, then it is considered the primary MaxScale instance, which means that it can handle automatic failover.

Configuring Cooperative Locking

1. Configure cooperative locking by configuring the cooperative_monitoring_locks parameter for the MariaDB Monitor in maxscale.cnf. It has several possible values.

Value	Description
none	Do not use any cooperative locking. This is the default value.
majority_of_all	Primary monitor requires locks on a majority of servers, even those which are down.
majority_of_running	Primary monitor requires locks on a majority of running servers.

For example:

[repl-cluster]
type                     = monitor
module                   = mariadbmon
...
cooperative_monitoring_locks = majority_of_running

1. Restart the MaxScale instance.

$ sudo systemctl restart maxscale

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