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Commit1a6d65b

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committed
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 parentc3437fb commit1a6d65b

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7 files changed

+77
-30
lines changed

7 files changed

+77
-30
lines changed

‎src/backend/catalog/index.c

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1010,6 +1010,7 @@ index_create(Relation heapRelation,
10101010
if (OidIsValid(parentIndexRelid))
10111011
{
10121012
StoreSingleInheritance(indexRelationId,parentIndexRelid,1);
1013+
LockRelationOid(parentIndexRelid,ShareUpdateExclusiveLock);
10131014
SetRelationHasSubclass(parentIndexRelid, true);
10141015
}
10151016

‎src/backend/commands/indexcmds.c

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -3762,7 +3762,10 @@ IndexSetParentIndex(Relation partitionIdx, Oid parentOid)
37623762

37633763
/* set relhassubclass if an index partition has been added to the parent */
37643764
if (OidIsValid(parentOid))
3765+
{
3766+
LockRelationOid(parentOid,ShareUpdateExclusiveLock);
37653767
SetRelationHasSubclass(parentOid, true);
3768+
}
37663769

37673770
/* set relispartition correctly on the partition */
37683771
update_relispartition(partRelid,OidIsValid(parentOid));

‎src/backend/commands/tablecmds.c

Lines changed: 14 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -3017,8 +3017,15 @@ findAttrByName(const char *attributeName, List *schema)
30173017
* SetRelationHasSubclass
30183018
*Set the value of the relation's relhassubclass field in pg_class.
30193019
*
3020-
* NOTE: caller must be holding an appropriate lock on the relation.
3021-
* ShareUpdateExclusiveLock is sufficient.
3020+
* It's always safe to set this field to true, because all SQL commands are
3021+
* ready to see true and then find no children. On the other hand, commands
3022+
* generally assume zero children if this is false.
3023+
*
3024+
* Caller must hold any self-exclusive lock until end of transaction. If the
3025+
* new value is false, caller must have acquired that lock before reading the
3026+
* evidence that justified the false value. That way, it properly waits if
3027+
* another backend is simultaneously concluding no need to change the tuple
3028+
* (new and old values are true).
30223029
*
30233030
* NOTE: an important side-effect of this operation is that an SI invalidation
30243031
* message is sent out to all backends --- including me --- causing plans
@@ -3033,6 +3040,11 @@ SetRelationHasSubclass(Oid relationId, bool relhassubclass)
30333040
HeapTupletuple;
30343041
Form_pg_class classtuple;
30353042

3043+
Assert(CheckRelationOidLockedByMe(relationId,
3044+
ShareUpdateExclusiveLock, false) ||
3045+
CheckRelationOidLockedByMe(relationId,
3046+
ShareRowExclusiveLock, true));
3047+
30363048
/*
30373049
* Fetch a modifiable copy of the tuple, modify it, update pg_class.
30383050
*/

‎src/backend/storage/lmgr/lmgr.c

Lines changed: 17 additions & 23 deletions
Original file line numberDiff line numberDiff line change
@@ -307,32 +307,26 @@ CheckRelationLockedByMe(Relation relation, LOCKMODE lockmode, bool orstronger)
307307
relation->rd_lockInfo.lockRelId.dbId,
308308
relation->rd_lockInfo.lockRelId.relId);
309309

310-
if (LockHeldByMe(&tag,lockmode))
311-
return true;
310+
return (orstronger ?
311+
LockOrStrongerHeldByMe(&tag,lockmode) :
312+
LockHeldByMe(&tag,lockmode));
313+
}
312314

313-
if (orstronger)
314-
{
315-
LOCKMODEslockmode;
315+
/*
316+
*CheckRelationOidLockedByMe
317+
*
318+
* Like the above, but takes an OID as argument.
319+
*/
320+
bool
321+
CheckRelationOidLockedByMe(Oidrelid,LOCKMODElockmode,boolorstronger)
322+
{
323+
LOCKTAGtag;
316324

317-
for (slockmode=lockmode+1;
318-
slockmode <=MaxLockMode;
319-
slockmode++)
320-
{
321-
if (LockHeldByMe(&tag,slockmode))
322-
{
323-
#ifdefNOT_USED
324-
/* Sometimes this might be useful for debugging purposes */
325-
elog(WARNING,"lock mode %s substituted for %s on relation %s",
326-
GetLockmodeName(tag.locktag_lockmethodid,slockmode),
327-
GetLockmodeName(tag.locktag_lockmethodid,lockmode),
328-
RelationGetRelationName(relation));
329-
#endif
330-
return true;
331-
}
332-
}
333-
}
325+
SetLocktagRelationOid(&tag,relid);
334326

335-
return false;
327+
return (orstronger ?
328+
LockOrStrongerHeldByMe(&tag,lockmode) :
329+
LockHeldByMe(&tag,lockmode));
336330
}
337331

338332
/*

‎src/backend/storage/lmgr/lock.c

Lines changed: 39 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -579,11 +579,17 @@ DoLockModesConflict(LOCKMODE mode1, LOCKMODE mode2)
579579
}
580580

581581
/*
582-
* LockHeldByMe -- test whether lock 'locktag' is held with mode 'lockmode'
583-
*by the current transaction
582+
* LockHeldByMeExtended -- test whether lock 'locktag' is held by the current
583+
*transaction
584+
*
585+
* Returns true if current transaction holds a lock on 'tag' of mode
586+
* 'lockmode'. If 'orstronger' is true, a stronger lockmode is also OK.
587+
* ("Stronger" is defined as "numerically higher", which is a bit
588+
* semantically dubious but is OK for the purposes we use this for.)
584589
*/
585-
bool
586-
LockHeldByMe(constLOCKTAG*locktag,LOCKMODElockmode)
590+
staticbool
591+
LockHeldByMeExtended(constLOCKTAG*locktag,
592+
LOCKMODElockmode,boolorstronger)
587593
{
588594
LOCALLOCKTAGlocaltag;
589595
LOCALLOCK*locallock;
@@ -599,7 +605,35 @@ LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode)
599605
(void*)&localtag,
600606
HASH_FIND,NULL);
601607

602-
return (locallock&&locallock->nLocks>0);
608+
if (locallock&&locallock->nLocks>0)
609+
return true;
610+
611+
if (orstronger)
612+
{
613+
LOCKMODEslockmode;
614+
615+
for (slockmode=lockmode+1;
616+
slockmode <=MaxLockMode;
617+
slockmode++)
618+
{
619+
if (LockHeldByMeExtended(locktag,slockmode, false))
620+
return true;
621+
}
622+
}
623+
624+
return false;
625+
}
626+
627+
bool
628+
LockHeldByMe(constLOCKTAG*locktag,LOCKMODElockmode)
629+
{
630+
returnLockHeldByMeExtended(locktag,lockmode, false);
631+
}
632+
633+
bool
634+
LockOrStrongerHeldByMe(constLOCKTAG*locktag,LOCKMODElockmode)
635+
{
636+
returnLockHeldByMeExtended(locktag,lockmode, true);
603637
}
604638

605639
#ifdefUSE_ASSERT_CHECKING

‎src/include/storage/lmgr.h

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -47,6 +47,8 @@ extern bool ConditionalLockRelation(Relation relation, LOCKMODE lockmode);
4747
externvoidUnlockRelation(Relationrelation,LOCKMODElockmode);
4848
externboolCheckRelationLockedByMe(Relationrelation,LOCKMODElockmode,
4949
boolorstronger);
50+
externboolCheckRelationOidLockedByMe(Oidrelid,LOCKMODElockmode,
51+
boolorstronger);
5052
externboolLockHasWaitersRelation(Relationrelation,LOCKMODElockmode);
5153

5254
externvoidLockRelationIdForSession(LockRelId*relid,LOCKMODElockmode);

‎src/include/storage/lock.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -558,6 +558,7 @@ extern void LockReleaseSession(LOCKMETHODID lockmethodid);
558558
externvoidLockReleaseCurrentOwner(LOCALLOCK**locallocks,intnlocks);
559559
externvoidLockReassignCurrentOwner(LOCALLOCK**locallocks,intnlocks);
560560
externboolLockHeldByMe(constLOCKTAG*locktag,LOCKMODElockmode);
561+
externboolLockOrStrongerHeldByMe(constLOCKTAG*locktag,LOCKMODElockmode);
561562
#ifdefUSE_ASSERT_CHECKING
562563
externHTAB*GetLockMethodLocalHash(void);
563564
#endif

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