Hot Standby and Recovery Conflicts
A hot standby does two jobs at once: it keeps replaying the primary's changes and it answers your read-only queries.
Sometimes those collide, when replay wants to remove data that a running query on the standby is still reading. PostgreSQL has to settle that tug-of-war, and this lesson is about how.
Pro members see the rest of this lesson
- A 4-step state diagram: Steady → Conflict → Delay → Cancel
- The full mechanism: what PostgreSQL does internally, in source terms
- 1 SQL query you can run, each labelled by how it was verified
- 1 transcript captured on PostgreSQL 17.10
- The closing insight, the mistake it prevents, and what it changes in your work
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Check it against the source1 citation in postgres/postgres · file, symbol and line verified on REL_17_STABLE
Primary symbol: ResolveRecoveryConflictWithSnapshot · line 467
Anchored to postgres/postgres on REL_17_STABLE and cross-checked against the manual for PostgreSQL 15–18. Every query here was run and its output captured on a throwaway PostgreSQL 17.10 lab; corrections are noted inline. §27.4 Hot Standby in the official docs →
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What comes before, after, and alongside it.
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