Although Galera Replication is synchronous, it is possible to deploy a Galera Replication cluster across data centers. Synchronous replication is traditionally implemented via 2-phase commit, where messages are sent to all nodes in a cluster in a ‘prepare’ phase, and another set of messages are sent in a ‘commit’ phase. This approach is usually not suitable for geographically disparate nodes, because of the latencies in sending messages between nodes.
Galera Replication makes use of certification based replication, that is a form of synchronous replication with reduced overhead.
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