HA orchestration (not engine source)🔒 Pro lesson
Failover and Fencing: Keeping One Writer (Ops Pattern)
Postgres can stream WAL to a standby, but deciding who is allowed to accept writes after a failure is usually handled by cluster software and fencing, not by one function inside the backend.
Learn it for production HA; study walsender, recovery, and slots for engine internals.
ProLesson body
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- A 4-step state diagram: Partition → Elect → Demote → Fence
- The full mechanism: what PostgreSQL does internally, in source terms
- 1 SQL query you can run, each labelled by how it was verified
- The closing insight, the mistake it prevents, and what it changes in your work
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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. §27.3 Failover in the official docs →
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