As per documentation: https://mariadb.com/kb/en/mariadb/documentation/re...

...plication-cluster-multi-master/galera/getting-started-with-mariadb-galera-cluster/

Disabling query_cache (and setting size to 0M so it doesn't allocate the RAM)
This is a huge reason for seeing deadlocks with Galera, hence the mandatory turning off

If only ever writing _AND_ reading from one Node this may be safe to leave as it is, but this type of thing easily gets forgotten.

PS There are very few deadlocks after doing this. May be worth revisiting master-master configuration (though as of Havana I know neutron_ovs still had some issue, neutron linux_bridge may not)