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Postgres cutovers must preserve synchronized logical replication slots

planetscale.com by Simeon Griggs 5 min read Editor score 7/10

A replica can replay all WAL yet still lack a synchronized, usable copy of logical replication slots, making promotion unsafe. The distinction matters when designing database failover and cutover procedures.

What
PlanetScale Postgres blocks a cutover when the replica lacks a synchronized, usable copy of logical replication slots.
How
WAL streams updates from the primary to replicas; logical slots decode WAL into change events for external subscribers.
Why it matters
Checking slots as well as replica data prevents cutovers that could make downstream applications miss events or stall.
writes updates decode change events primary WAL replicas logicalreplication externalsubscribers
WAL keeps replicas synchronized while logical slots deliver change events to external subscribers. Sketched from the article's own text.

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