Do plain SELECT readers block writers in PostgreSQL?

Question

Accepted Answer

No — SELECTs read a snapshot and take no locks that conflict with data modification — Thanks to MVCC, plain reads never block UPDATE or DELETE (and writers don't block readers). SELECT takes no row locks (SELECT FOR UPDATE is the explicit exception), transaction wrapping doesn't change that, and indexes don't serialize readers with writers.

Answer

Yes — every SELECT takes shared row locks that writers must wait for and acquire

Answer

Only inside explicit transactions — autocommitted reads skip the locking entirely

Answer

Only on indexed tables — the index maintenance serializes readers with writers

Do plain SELECT readers block writers in PostgreSQL?

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