Hi, Le lun. 20 mai 2024 à 11:27, PetSerAl <petse...@gmail.com> a écrit :
> How pg_dump interact with not MVCC-safe commands? > > As I understand, pg_dump first take snapshot and then lock all tables > it intended to dump. What happens if not MVCC-safe command committed > after snapshot but before lock? From comment to pg_dump.c I understand > that it may fail with 'cache lookup failed' error. But, can it happen, > that pg_dump not fail, but instead capture inconsistent dump? For > example TRUNCATE committed after snapshot and pg_dump will see result > of TRUNCATE but not result of other commands in TRUNCATE transaction? > > > You can't truncate an already existing table while pg_dump is running. TRUNCATE needs an exclusive lock, and pg_dump already has a lock on all tables of the database it's dumping. So TRUNCATE will be blocked until pg_dump finishes all its work. (The same will happen for VACUUM FULL, CLUSTER and some (all?) ALTER TABLE commands.) -- Guillaume.
