Using Cooperative Locking for HA with MaxScale's MariaDB Monitor

This page is part of MariaDB's Documentation.

The parent of this page is: MariaDB Monitor

Topics on this page:

Overview
How MariaDB Monitor uses Cooperative Locks
Configuring Cooperative Locking

Overview

MaxScale's MariaDB Monitor (mariadbmon) monitors MariaDB replication 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

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

Restart the MaxScale instance.
```
$ sudo systemctl restart maxscale
```