MySQL Replication is part of the standard MySQL database, and is mainly asynchronous in nature. Updates are always done on one master, and these are propagated to slaves. It is possible to create a ring topology with multiple masters, however this is not recommended as it is very easy for the servers to get out of sync in case of a master failing. There is no automatic failover or resynchronization in these cases.
Galera Replication is a plug-in to MySQL, and enables a true master-master setup for InnoDB. In a Galera Replication cluster, all nodes are masters and applications can read and write from any node. Transactions are synchronously committed on all nodes. In case of a node failing, the other nodes will continue to operate and kept up to date. When the failed node comes up again, it automatically synchronizes with the other nodes before it is allowed back into the cluster. No data is lost when a node fails.
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