Multi-AZ PostgreSQL COMMIT wait events: WALSync, SyncRep & XactSync

When deploying your PostgreSQL application on AWS, you can replicate the database to multiple Availability Zones to failover in case of failures. This is commonly referred to as "Multi-AZ", but this covers different options, and the documentation on how it works is not comprehensive. To achieve failover with a Recovery Point Objective (RPO) of zero, the replication must be synchronous to ensure that all changes are replicated when your commit is successful. When PostgreSQL waits, the reason is exposed …

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