Multi Master Galera

Support Status Test Case
Experimental 0
replication-multi-master-wsrep (2.0)
Item Value
Description Enable Multi Master Galera
Type boolean
Default Value false

Galera cluster is not always adapted for a Write to all node architecture, for those reasons:

  • It do not support serialized isolation level, READ LOCKS acquire no cluster locks and can only be validated for REPEATABLE READ or SERIALIZED on the local node the transaction is executed.

  • It increase deadlock probability, while transactions are replicated in concurrency it's style take time to round trip the network, certification only apply on checkpointing, so the more nodes the more latency the more deadlock the workload may be exposed.

For those reasons your application as to be modify to write critical sections on a leader Galera node.

replication-manager can help you to get the best of Galera combine with layer7 proxy like MaxScale or ProxySQL.

replication-manager will elect a virtual master and failover or switchover it based on each Galera node status, if one node get excluded for any reason of that cluster.

replication-manager could help to get 2 node Galera Cluster with one replication-manager on each node and a replication-manager-arb to manage active-passive role on each. The active replication-manager can be use to start garbd and enable the cluster to survive.

Supported versions and SST authentication

When replication-manager provisions the Galera cluster (an orchestrator renders the database configuration, not on premise), the root password is never written in that configuration:

  • The SST (State Snapshot Transfer) authenticates the account mysql@localhost through unix_socket, with no password: wsrep_sst_auth=mysql:. The donor's mariabackup runs as the mysql OS user, so the socket authentication matches.
  • The account is created when the first node's datadir is initialized, before any node joins, and replication-manager keeps it present on running clusters. While it cannot be created, the security ERROR ERR00114 is open.
  • MariaDB 10.4 or later is required. unix_socket is built in from 10.4. MariaDB 10.3 and older are no longer supported on a provisioned Galera topology: each such server raises the ERROR ERR00115 until it is upgraded.
  • MySQL and Percona keep their wsrep_sst_auth until the xtrabackup SST over auth_socket is validated.

On premise, replication-manager renders no configuration and these rules do not apply.