Using Cooperative Locking for HA with MaxScale's MariaDB Monitor
Overview
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 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
2. Restart the MaxScale instance.
$ sudo systemctl restart maxscale
