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Commit112d055

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Lock owned sequences during ALTER TABLE SET { LOGGED | UNLOGGED }.
These commands already make the persistence of owned sequences followowned table persistence changes. They didn't lock those sequences.They lost the effect of nextval() calls that other sessions make afterthe ALTER TABLE command, before the ALTER TABLE transaction commits.Fix by acquiring the same lock that ALTER SEQUENCE SET { LOGGED |UNLOGGED } acquires. This might cause more deadlocks. Back-patch tov15, where commit344d62f introducedunlogged sequences.Reviewed (in an earlier version) by Robert Haas.Discussion:https://postgr.es/m/20240611024525.9f.nmisch@google.com
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‎src/backend/commands/sequence.c

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@@ -557,6 +557,13 @@ SequenceChangePersistence(Oid relid, char newrelpersistence)
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Bufferbuf;
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HeapTupleDataseqdatatuple;
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/*
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* ALTER SEQUENCE acquires this lock earlier. If we're processing an
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* owned sequence for ALTER TABLE, lock now. Without the lock, we'd
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* discard increments from nextval() calls (in other sessions) between
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* this function's buffer unlock and this transaction's commit.
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*/
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LockRelationOid(relid,AccessExclusiveLock);
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init_sequence(relid,&elm,&seqrel);
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/* check the comment above nextval_internal()'s equivalent call. */

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