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Commit706054b

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Ensure we have a snapshot when updating various system catalogs.
A few places that access system catalogs don't set up an activesnapshot before potentially accessing their TOAST tables. To fix,push an active snapshot just before each section of code that mightrequire accessing one of these TOAST tables, and pop it shortlyafterwards. While at it, this commit adds some rather strictassertions in an attempt to prevent such issues in the future.Commit16bf24e recently removed pg_replication_origin's TOASTtable in order to fix the same problem for that catalog. On theback-branches, those bugs are left in place. We cannot easilyremove a catalog's TOAST table on released major versions, and onlyreplication origins with extremely long names are affected. Giventhe low severity of the issue, fixing older versions doesn't seemworth the trouble of significantly modifying the patch.Also, on v13 and v14, the aforementioned strict assertions havebeen omitted because commit2776922, which addedHaveRegisteredOrActiveSnapshot(), was not back-patched. While wecould probably back-patch it now, I've opted against it because itseems unlikely that new TOAST snapshot issues will be introduced inthe oldest supported versions.Reported-by: Alexander Lakhin <exclusion@gmail.com>Reviewed-by: Michael Paquier <michael@paquier.xyz>Discussion:https://postgr.es/m/18127-fe54b6a667f29658%40postgresql.orgDiscussion:https://postgr.es/m/18309-c0bf914950c46692%40postgresql.orgDiscussion:https://postgr.es/m/ZvMSUPOqUU-VNADN%40nathanBackpatch-through: 13
1 parent232d8ca commit706054b

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5 files changed

+69
-1
lines changed

5 files changed

+69
-1
lines changed

‎src/backend/access/heap/heapam.c

Lines changed: 29 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -213,6 +213,27 @@ static const int MultiXactStatusLock[MaxMultiXactStatus + 1] =
213213
#defineTUPLOCK_from_mxstatus(status) \
214214
(MultiXactStatusLock[(status)])
215215

216+
/*
217+
* Check that we have a valid snapshot if we might need TOAST access.
218+
*/
219+
staticinlinevoid
220+
AssertHasSnapshotForToast(Relationrel)
221+
{
222+
#ifdefUSE_ASSERT_CHECKING
223+
224+
/* bootstrap mode in particular breaks this rule */
225+
if (!IsNormalProcessingMode())
226+
return;
227+
228+
/* if the relation doesn't have a TOAST table, we are good */
229+
if (!OidIsValid(rel->rd_rel->reltoastrelid))
230+
return;
231+
232+
Assert(HaveRegisteredOrActiveSnapshot());
233+
234+
#endif/* USE_ASSERT_CHECKING */
235+
}
236+
216237
/* ----------------------------------------------------------------
217238
* heap support routines
218239
* ----------------------------------------------------------------
@@ -2066,6 +2087,8 @@ heap_insert(Relation relation, HeapTuple tup, CommandId cid,
20662087
Assert(HeapTupleHeaderGetNatts(tup->t_data) <=
20672088
RelationGetNumberOfAttributes(relation));
20682089

2090+
AssertHasSnapshotForToast(relation);
2091+
20692092
/*
20702093
* Fill in tuple header fields and toast the tuple if necessary.
20712094
*
@@ -2343,6 +2366,8 @@ heap_multi_insert(Relation relation, TupleTableSlot **slots, int ntuples,
23432366
/* currently not needed (thus unsupported) for heap_multi_insert() */
23442367
Assert(!(options&HEAP_INSERT_NO_LOGICAL));
23452368

2369+
AssertHasSnapshotForToast(relation);
2370+
23462371
needwal=RelationNeedsWAL(relation);
23472372
saveFreeSpace=RelationGetTargetPageFreeSpace(relation,
23482373
HEAP_DEFAULT_FILLFACTOR);
@@ -2765,6 +2790,8 @@ heap_delete(Relation relation, ItemPointer tid,
27652790

27662791
Assert(ItemPointerIsValid(tid));
27672792

2793+
AssertHasSnapshotForToast(relation);
2794+
27682795
/*
27692796
* Forbid this during a parallel operation, lest it allocate a combo CID.
27702797
* Other workers might need that combo CID for visibility checks, and we
@@ -3260,6 +3287,8 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
32603287
Assert(HeapTupleHeaderGetNatts(newtup->t_data) <=
32613288
RelationGetNumberOfAttributes(relation));
32623289

3290+
AssertHasSnapshotForToast(relation);
3291+
32633292
/*
32643293
* Forbid this during a parallel operation, lest it allocate a combo CID.
32653294
* Other workers might need that combo CID for visibility checks, and we

‎src/backend/commands/indexcmds.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -4226,7 +4226,7 @@ ReindexRelationConcurrently(const ReindexStmt *stmt, Oid relationOid, const Rein
42264226
false);
42274227

42284228
/*
4229-
*Updating pg_index might involve TOAST table access, so ensure we
4229+
*Swapping the indexes might involve TOAST table access, so ensure we
42304230
* have a valid snapshot.
42314231
*/
42324232
PushActiveSnapshot(GetTransactionSnapshot());

‎src/backend/commands/tablecmds.c

Lines changed: 8 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -20964,9 +20964,17 @@ ATExecDetachPartition(List **wqueue, AlteredTableInfo *tab, Relation rel,
2096420964
tab->rel = rel;
2096520965
}
2096620966

20967+
/*
20968+
* Detaching the partition might involve TOAST table access, so ensure we
20969+
* have a valid snapshot.
20970+
*/
20971+
PushActiveSnapshot(GetTransactionSnapshot());
20972+
2096720973
/* Do the final part of detaching */
2096820974
DetachPartitionFinalize(rel, partRel, concurrent, defaultPartOid);
2096920975

20976+
PopActiveSnapshot();
20977+
2097020978
ObjectAddressSet(address, RelationRelationId, RelationGetRelid(partRel));
2097120979

2097220980
/* keep our lock until commit */

‎src/backend/postmaster/autovacuum.c

Lines changed: 7 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2234,6 +2234,12 @@ do_autovacuum(void)
22342234
get_namespace_name(classForm->relnamespace),
22352235
NameStr(classForm->relname))));
22362236

2237+
/*
2238+
* Deletion might involve TOAST table access, so ensure we have a
2239+
* valid snapshot.
2240+
*/
2241+
PushActiveSnapshot(GetTransactionSnapshot());
2242+
22372243
object.classId=RelationRelationId;
22382244
object.objectId=relid;
22392245
object.objectSubId=0;
@@ -2246,6 +2252,7 @@ do_autovacuum(void)
22462252
* To commit the deletion, end current transaction and start a new
22472253
* one. Note this also releases the locks we took.
22482254
*/
2255+
PopActiveSnapshot();
22492256
CommitTransactionCommand();
22502257
StartTransactionCommand();
22512258

‎src/backend/replication/logical/worker.c

Lines changed: 24 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -4626,8 +4626,16 @@ run_apply_worker()
46264626
walrcv_startstreaming(LogRepWorkerWalRcvConn,&options);
46274627

46284628
StartTransactionCommand();
4629+
4630+
/*
4631+
* Updating pg_subscription might involve TOAST table access, so
4632+
* ensure we have a valid snapshot.
4633+
*/
4634+
PushActiveSnapshot(GetTransactionSnapshot());
4635+
46294636
UpdateTwoPhaseState(MySubscription->oid,LOGICALREP_TWOPHASE_STATE_ENABLED);
46304637
MySubscription->twophasestate=LOGICALREP_TWOPHASE_STATE_ENABLED;
4638+
PopActiveSnapshot();
46314639
CommitTransactionCommand();
46324640
}
46334641
else
@@ -4843,7 +4851,15 @@ DisableSubscriptionAndExit(void)
48434851

48444852
/* Disable the subscription */
48454853
StartTransactionCommand();
4854+
4855+
/*
4856+
* Updating pg_subscription might involve TOAST table access, so ensure we
4857+
* have a valid snapshot.
4858+
*/
4859+
PushActiveSnapshot(GetTransactionSnapshot());
4860+
48464861
DisableSubscription(MySubscription->oid);
4862+
PopActiveSnapshot();
48474863
CommitTransactionCommand();
48484864

48494865
/* Ensure we remove no-longer-useful entry for worker's start time */
@@ -4947,6 +4963,12 @@ clear_subscription_skip_lsn(XLogRecPtr finish_lsn)
49474963
started_tx= true;
49484964
}
49494965

4966+
/*
4967+
* Updating pg_subscription might involve TOAST table access, so ensure we
4968+
* have a valid snapshot.
4969+
*/
4970+
PushActiveSnapshot(GetTransactionSnapshot());
4971+
49504972
/*
49514973
* Protect subskiplsn of pg_subscription from being concurrently updated
49524974
* while clearing it.
@@ -5005,6 +5027,8 @@ clear_subscription_skip_lsn(XLogRecPtr finish_lsn)
50055027
heap_freetuple(tup);
50065028
table_close(rel,NoLock);
50075029

5030+
PopActiveSnapshot();
5031+
50085032
if (started_tx)
50095033
CommitTransactionCommand();
50105034
}

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