Using SST Donors for Queries with MaxScale's Galera Monitor
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
Configure the availability of SST donors by configuring the
available_when_donorparameter for the Galera Monitor in
[galera-cluster] type = monitor module = galeramon ... available_when_donor = true
Restart the MaxScale instance.
$ sudo systemctl restart maxscale