If a Galera Cluster node is also a replication master, then some additional configuration may be needed.
If the node is a replication master, then its replication slaves only replicate transactions which are in the binary log, so this means that the transactions that correspond to Galera Cluster write-sets would not be replicated by any replication slaves by default. If you would like a node to write its replicated write sets to the binary log, then you will have to set
log_slave_updates=ON. If the node has any replication slaves, then this would also allow those slaves to replicate the transactions that corresponded to those write sets.
See Configuring MariaDB Galera Cluster: Writing Replicated Write Sets to the Binary Log for more information.
If a Galera Cluster node is also a replication slave, then some additional configuration may be needed.
If the node is a replication slave, then the node's slave SQL thread will be applying transactions that it replicates from its replication master. Transactions applied by the slave SQL thread will only generate Galera Cluster write-sets if the node has
log_slave_updates=ON set. Therefore, in order to replicate these transactions to the rest of the nodes in the cluster,
log_slave_updates=ON must be set.
Both MariaDB replication and MariaDB Galera Cluster support replication filters, so extra caution must be taken when using all of these features together. See Configuring MariaDB Galera Cluster: Replication Filters for more details on how MariaDB Galera Cluster interprets replication filters.
It is most common to set
server_id to the same value on each node in a given cluster. Since MariaDB Galera Cluster uses a virtually synchronous certification-based replication, all nodes should have the same data, so in a logical sense, a cluster can be considered in many cases a single logical server for purposes related to MariaDB replication. The binary logs of each cluster node might even contain roughly the same transactions and GTIDs if
log_slave_updates=ON is set and if wsrep GTID mode is enabled and if non-Galera transactions are not being executed on any nodes.
There are cases when it might make sense to set a different
server_id value on each node in a given cluster. For example, if
log_slave_updates=OFF is set and if another cluster or a standard MariaDB Server is using multi-source replication to replicate transactions from each cluster node individually, then it would be required to set a different
server_id value on each node for this to work.
Keep in mind that if replication is set up in a scenario where each cluster node has a different
server_id value, and if the replication topology is set up in such a way that a cluster node can replicate the same transactions through Galera and through MariaDB replication, then you may need to configure the cluster node to ignore these transactions when setting up MariaDB replication. You can do so by setting
IGNORE_SERVER_IDS to the server IDs of all nodes in the same cluster when executing
CHANGE MASTER TO. For example, this might be required when circular replication is set up between two separate clusters, and each cluster node as a different
server_id value, and each cluster has
© 2019 MariaDB
Licensed under the Creative Commons Attribution 3.0 Unported License and the GNU Free Documentation License.