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Commit0cecc90

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Lock before setting relhassubclass on RELKIND_PARTITIONED_INDEX.
Commit5b56264 added a comment thatSetRelationHasSubclass() callers must hold this lock. When commit17f206f extended use of this column topartitioned indexes, it didn't take the lock. As the latter commitmessage mentioned, we currently never reset a partitioned index torelhassubclass=f. That largely avoids harm from the lock omission. Thecause for fixing this now is to unblock introducing a rule about locksrequired to heap_update() a pg_class row. This might cause moredeadlocks. It gives minor user-visible benefits:- If an ALTER INDEX SET TABLESPACE runs concurrently with ALTER TABLE ATTACH PARTITION or CREATE PARTITION OF, one transaction blocks instead of failing with "tuple concurrently updated". (Many cases of DDL concurrency still fail that way.)- Match ALTER INDEX ATTACH PARTITION in choosing to lock the index.While not user-visible today, we'll need this if we ever make somethingset the flag to false for a partitioned index, like ANALYZE does todayfor tables. Back-patch to v12 (all supported versions), the plan forthe commit relying on the new rule. In back branches, addLockOrStrongerHeldByMe() instead of adding a LockHeldByMe() parameter.Reviewed (in an earlier version) by Robert Haas.Discussion:https://postgr.es/m/20240611024525.9f.nmisch@google.com
1 parentf88cdb3 commit0cecc90

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7 files changed

+61
-30
lines changed

7 files changed

+61
-30
lines changed

‎src/backend/catalog/index.c

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1058,6 +1058,7 @@ index_create(Relation heapRelation,
10581058
if (OidIsValid(parentIndexRelid))
10591059
{
10601060
StoreSingleInheritance(indexRelationId,parentIndexRelid,1);
1061+
LockRelationOid(parentIndexRelid,ShareUpdateExclusiveLock);
10611062
SetRelationHasSubclass(parentIndexRelid, true);
10621063
}
10631064

‎src/backend/commands/indexcmds.c

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -4355,7 +4355,10 @@ IndexSetParentIndex(Relation partitionIdx, Oid parentOid)
43554355

43564356
/* set relhassubclass if an index partition has been added to the parent */
43574357
if (OidIsValid(parentOid))
4358+
{
4359+
LockRelationOid(parentOid,ShareUpdateExclusiveLock);
43584360
SetRelationHasSubclass(parentOid, true);
4361+
}
43594362

43604363
/* set relispartition correctly on the partition */
43614364
update_relispartition(partRelid,OidIsValid(parentOid));

‎src/backend/commands/tablecmds.c

Lines changed: 14 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -3483,8 +3483,15 @@ findAttrByName(const char *attributeName, const List *columns)
34833483
* SetRelationHasSubclass
34843484
*Set the value of the relation's relhassubclass field in pg_class.
34853485
*
3486-
* NOTE: caller must be holding an appropriate lock on the relation.
3487-
* ShareUpdateExclusiveLock is sufficient.
3486+
* It's always safe to set this field to true, because all SQL commands are
3487+
* ready to see true and then find no children. On the other hand, commands
3488+
* generally assume zero children if this is false.
3489+
*
3490+
* Caller must hold any self-exclusive lock until end of transaction. If the
3491+
* new value is false, caller must have acquired that lock before reading the
3492+
* evidence that justified the false value. That way, it properly waits if
3493+
* another backend is simultaneously concluding no need to change the tuple
3494+
* (new and old values are true).
34883495
*
34893496
* NOTE: an important side-effect of this operation is that an SI invalidation
34903497
* message is sent out to all backends --- including me --- causing plans
@@ -3499,6 +3506,11 @@ SetRelationHasSubclass(Oid relationId, bool relhassubclass)
34993506
HeapTupletuple;
35003507
Form_pg_class classtuple;
35013508

3509+
Assert(CheckRelationOidLockedByMe(relationId,
3510+
ShareUpdateExclusiveLock, false) ||
3511+
CheckRelationOidLockedByMe(relationId,
3512+
ShareRowExclusiveLock, true));
3513+
35023514
/*
35033515
* Fetch a modifiable copy of the tuple, modify it, update pg_class.
35043516
*/

‎src/backend/storage/lmgr/lmgr.c

Lines changed: 13 additions & 23 deletions
Original file line numberDiff line numberDiff line change
@@ -335,32 +335,22 @@ CheckRelationLockedByMe(Relation relation, LOCKMODE lockmode, bool orstronger)
335335
relation->rd_lockInfo.lockRelId.dbId,
336336
relation->rd_lockInfo.lockRelId.relId);
337337

338-
if (LockHeldByMe(&tag,lockmode))
339-
return true;
338+
returnLockHeldByMe(&tag,lockmode,orstronger);
339+
}
340340

341-
if (orstronger)
342-
{
343-
LOCKMODEslockmode;
341+
/*
342+
*CheckRelationOidLockedByMe
343+
*
344+
* Like the above, but takes an OID as argument.
345+
*/
346+
bool
347+
CheckRelationOidLockedByMe(Oidrelid,LOCKMODElockmode,boolorstronger)
348+
{
349+
LOCKTAGtag;
344350

345-
for (slockmode=lockmode+1;
346-
slockmode <=MaxLockMode;
347-
slockmode++)
348-
{
349-
if (LockHeldByMe(&tag,slockmode))
350-
{
351-
#ifdefNOT_USED
352-
/* Sometimes this might be useful for debugging purposes */
353-
elog(WARNING,"lock mode %s substituted for %s on relation %s",
354-
GetLockmodeName(tag.locktag_lockmethodid,slockmode),
355-
GetLockmodeName(tag.locktag_lockmethodid,lockmode),
356-
RelationGetRelationName(relation));
357-
#endif
358-
return true;
359-
}
360-
}
361-
}
351+
SetLocktagRelationOid(&tag,relid);
362352

363-
returnfalse;
353+
returnLockHeldByMe(&tag,lockmode,orstronger);
364354
}
365355

366356
/*

‎src/backend/storage/lmgr/lock.c

Lines changed: 26 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -578,11 +578,17 @@ DoLockModesConflict(LOCKMODE mode1, LOCKMODE mode2)
578578
}
579579

580580
/*
581-
* LockHeldByMe -- test whether lock 'locktag' is held with mode 'lockmode'
582-
*by the current transaction
581+
* LockHeldByMe -- test whether lock 'locktag' is held by the current
582+
*transaction
583+
*
584+
* Returns true if current transaction holds a lock on 'tag' of mode
585+
* 'lockmode'. If 'orstronger' is true, a stronger lockmode is also OK.
586+
* ("Stronger" is defined as "numerically higher", which is a bit
587+
* semantically dubious but is OK for the purposes we use this for.)
583588
*/
584589
bool
585-
LockHeldByMe(constLOCKTAG*locktag,LOCKMODElockmode)
590+
LockHeldByMe(constLOCKTAG*locktag,
591+
LOCKMODElockmode,boolorstronger)
586592
{
587593
LOCALLOCKTAGlocaltag;
588594
LOCALLOCK*locallock;
@@ -598,7 +604,23 @@ LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode)
598604
&localtag,
599605
HASH_FIND,NULL);
600606

601-
return (locallock&&locallock->nLocks>0);
607+
if (locallock&&locallock->nLocks>0)
608+
return true;
609+
610+
if (orstronger)
611+
{
612+
LOCKMODEslockmode;
613+
614+
for (slockmode=lockmode+1;
615+
slockmode <=MaxLockMode;
616+
slockmode++)
617+
{
618+
if (LockHeldByMe(locktag,slockmode, false))
619+
return true;
620+
}
621+
}
622+
623+
return false;
602624
}
603625

604626
#ifdefUSE_ASSERT_CHECKING

‎src/include/storage/lmgr.h

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -48,6 +48,8 @@ extern bool ConditionalLockRelation(Relation relation, LOCKMODE lockmode);
4848
externvoidUnlockRelation(Relationrelation,LOCKMODElockmode);
4949
externboolCheckRelationLockedByMe(Relationrelation,LOCKMODElockmode,
5050
boolorstronger);
51+
externboolCheckRelationOidLockedByMe(Oidrelid,LOCKMODElockmode,
52+
boolorstronger);
5153
externboolLockHasWaitersRelation(Relationrelation,LOCKMODElockmode);
5254

5355
externvoidLockRelationIdForSession(LockRelId*relid,LOCKMODElockmode);

‎src/include/storage/lock.h

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -567,7 +567,8 @@ extern void LockReleaseAll(LOCKMETHODID lockmethodid, bool allLocks);
567567
externvoidLockReleaseSession(LOCKMETHODIDlockmethodid);
568568
externvoidLockReleaseCurrentOwner(LOCALLOCK**locallocks,intnlocks);
569569
externvoidLockReassignCurrentOwner(LOCALLOCK**locallocks,intnlocks);
570-
externboolLockHeldByMe(constLOCKTAG*locktag,LOCKMODElockmode);
570+
externboolLockHeldByMe(constLOCKTAG*locktag,
571+
LOCKMODElockmode,boolorstronger);
571572
#ifdefUSE_ASSERT_CHECKING
572573
externHTAB*GetLockMethodLocalHash(void);
573574
#endif

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