Using SST Donors for Queries with MaxScale's Galera Monitor

MaxScale's Galera Monitor (galeramon) monitors Galera Cluster deployments.

By default, when a node is chosen as a donor for a State Snapshot Transfer (SST), Galera Monitor does not route any queries to it. However, some SST methods are non-blocking on the donor, so this default behavior is not always desired.

Non-Blocking SST Methods

A cluster's SST method is defined by the wsrep_sst_method system variable. When this system variable is set to mariabackup, the cluster uses MariaDB Backup to perform the SST. MariaDB Backup is a non-blocking backup method, so Galera Cluster allows the node to execute queries while acting as the SST donor.

Configuring Availability of SST Donors

  1. Configure the availability of SST donors by configuring the available_when_donor parameter for the Galera Monitor in maxscale.cnf.

    For example:

    [galera-cluster]
    type                     = monitor
    module                   = galeramon
    ...
    available_when_donor     = true
    
  2. Restart the MaxScale instance.

    $ sudo systemctl restart maxscale