Multi-source replication means that one server can have multiple masters from which it replicates. Why multi-source? One good reason is to consolidate databases (e.g. merge your shards) for analytical reporting or as a centralized backup server. MariaDB 10 already has this feature, and MySQL 5.7 will also support it.
It is possible to set up your Galera Cluster as an aggregator of your masters in a multi-source replication setup, we’ll walk you through the steps in this blog. Note that the howto is for Galera Cluster for MySQL (Codership) and Percona XtraDB Cluster. In a separate post, we’ll show you how to configure MariaDB Cluster 10 instead. If you would like to use MySQL Cluster (NDB) as aggregator, then check out this blog.
Galera Cluster as Aggregator/Slave
Galera cluster can operate both as MySQL master and slave. Each Galera node can act as a slave channel accepting replication from a master. The number of slave channels should be equal or less to the number of Galera master nodes in the cluster. So, if you have a three-node Galera cluster, you can have up to three different replication sources connected to it. Note that in MariaDB Galera Cluster 10, you can configure as many sources as you want since each node supports multi-source replication.
To achieve multi-source replication in MySQL 5.6, you cannot have GTID enabled for Galera Cluster. GTID will cause our Galera cluster to work as a single unit (imagine one single slave server), since it globally preserves the MySQL GTID events on the cluster. So the cluster will not be able to replicate from more than one master. Hence, we will use the “legacy” way to determine the starting binary log file and position. On a side note, enabling GTID is highly recommended if your Galera Cluster acts as a MySQL master, as described in this blog post.
We will setup multi-source replication as below:
We have 3 standalone MySQL servers (masters), and each master has a separate database: mydb1, mydb2 and mydb3. We would like to consolidate all 3 databases into our Galera cluster.
Setting Up Masters
1. On each standalone MySQL server, configure it as a master by adding a server ID, enabling binary logging with ROW format:
# mysql1 my.cnf server-id=101 log-bin=binlog binlog-format=ROW
# mysql2 my.cnf server-id=102 log-bin=binlog binlog-format=ROW
# mysql3 my.cnf server-id=103 log-bin=binlog binlog-format=ROW