From ac77516715c7d05e94f585a08253e43c64a91382 Mon Sep 17 00:00:00 2001 From: Nathan Bossart Date: Tue, 27 May 2025 14:58:37 -0500 Subject: [PATCH v6 1/1] Ensure we have a snapshot when updating various system catalogs. A few places that access system catalogs don't set up an active snapshot before potentially accessing their TOAST tables. To fix, push an active snapshot just before each section of code that might require accessing one of these TOAST tables, and pop it shortly afterwards. While at it, this commit adds some rather strict assertions in an attempt to prevent such issues in the future. Commit 16bf24e0e4 recently removed pg_replication_origin's TOAST table in order to fix the same problem for that catalog. On the back-branches, those bugs are left in place. We cannot easily remove a catalog's TOAST table on released major versions, and only replication origins with extremely long names are affected. Given the low severity of the issue, it didn't seem worth the trouble of significantly modifying the patch on the back-branches. Also, on v13 and v14, the aforementioned strict assertions have been omitted because commit 2776922201, which added HaveRegisteredOrActiveSnapshot(), was not backpatched. While we could probably back-patch it now, I've opted against it because it seems unlikely that new TOAST snapshot issues will be introduced in the oldest supported versions. Reported-by: Alexander Lakhin Reviewed-by: Michael Paquier Discussion: https://postgr.es/m/18127-fe54b6a667f29658%40postgresql.org Discussion: https://postgr.es/m/18309-c0bf914950c46692%40postgresql.org Discussion: https://postgr.es/m/ZvMSUPOqUU-VNADN%40nathan Backpatch-through: 13 --- src/backend/access/heap/heapam.c | 29 ++++++++++++++++++++++++ src/backend/commands/indexcmds.c | 2 +- src/backend/commands/tablecmds.c | 8 +++++++ src/backend/postmaster/autovacuum.c | 7 ++++++ src/backend/replication/logical/worker.c | 24 ++++++++++++++++++++ 5 files changed, 69 insertions(+), 1 deletion(-) diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c index 9ec8cda1c68..2be7f817c78 100644 --- a/src/backend/access/heap/heapam.c +++ b/src/backend/access/heap/heapam.c @@ -213,6 +213,27 @@ static const int MultiXactStatusLock[MaxMultiXactStatus + 1] = #define TUPLOCK_from_mxstatus(status) \ (MultiXactStatusLock[(status)]) +/* + * Check that we have a valid snapshot if we might need TOAST access. + */ +static inline void +AssertHasSnapshotForToast(Relation rel) +{ +#ifdef USE_ASSERT_CHECKING + + /* bootstrap mode in particular breaks this rule */ + if (!IsNormalProcessingMode()) + return; + + /* if the relation doesn't have a TOAST table, we are good */ + if (!OidIsValid(rel->rd_rel->reltoastrelid)) + return; + + Assert(HaveRegisteredOrActiveSnapshot()); + +#endif /* USE_ASSERT_CHECKING */ +} + /* ---------------------------------------------------------------- * heap support routines * ---------------------------------------------------------------- @@ -2066,6 +2087,8 @@ heap_insert(Relation relation, HeapTuple tup, CommandId cid, Assert(HeapTupleHeaderGetNatts(tup->t_data) <= RelationGetNumberOfAttributes(relation)); + AssertHasSnapshotForToast(relation); + /* * Fill in tuple header fields and toast the tuple if necessary. * @@ -2343,6 +2366,8 @@ heap_multi_insert(Relation relation, TupleTableSlot **slots, int ntuples, /* currently not needed (thus unsupported) for heap_multi_insert() */ Assert(!(options & HEAP_INSERT_NO_LOGICAL)); + AssertHasSnapshotForToast(relation); + needwal = RelationNeedsWAL(relation); saveFreeSpace = RelationGetTargetPageFreeSpace(relation, HEAP_DEFAULT_FILLFACTOR); @@ -2765,6 +2790,8 @@ heap_delete(Relation relation, ItemPointer tid, Assert(ItemPointerIsValid(tid)); + AssertHasSnapshotForToast(relation); + /* * Forbid this during a parallel operation, lest it allocate a combo CID. * Other workers might need that combo CID for visibility checks, and we @@ -3260,6 +3287,8 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup, Assert(HeapTupleHeaderGetNatts(newtup->t_data) <= RelationGetNumberOfAttributes(relation)); + AssertHasSnapshotForToast(relation); + /* * Forbid this during a parallel operation, lest it allocate a combo CID. * Other workers might need that combo CID for visibility checks, and we diff --git a/src/backend/commands/indexcmds.c b/src/backend/commands/indexcmds.c index d962fe392cd..c3ec2076a52 100644 --- a/src/backend/commands/indexcmds.c +++ b/src/backend/commands/indexcmds.c @@ -4226,7 +4226,7 @@ ReindexRelationConcurrently(const ReindexStmt *stmt, Oid relationOid, const Rein false); /* - * Updating pg_index might involve TOAST table access, so ensure we + * Swapping the indexes might involve TOAST table access, so ensure we * have a valid snapshot. */ PushActiveSnapshot(GetTransactionSnapshot()); diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c index 54ad38247aa..acf11e83c04 100644 --- a/src/backend/commands/tablecmds.c +++ b/src/backend/commands/tablecmds.c @@ -20964,9 +20964,17 @@ ATExecDetachPartition(List **wqueue, AlteredTableInfo *tab, Relation rel, tab->rel = rel; } + /* + * Detaching the partition might involve TOAST table access, so ensure we + * have a valid snapshot. + */ + PushActiveSnapshot(GetTransactionSnapshot()); + /* Do the final part of detaching */ DetachPartitionFinalize(rel, partRel, concurrent, defaultPartOid); + PopActiveSnapshot(); + ObjectAddressSet(address, RelationRelationId, RelationGetRelid(partRel)); /* keep our lock until commit */ diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c index 981be42e3af..451fb90a610 100644 --- a/src/backend/postmaster/autovacuum.c +++ b/src/backend/postmaster/autovacuum.c @@ -2234,6 +2234,12 @@ do_autovacuum(void) get_namespace_name(classForm->relnamespace), NameStr(classForm->relname)))); + /* + * Deletion might involve TOAST table access, so ensure we have a + * valid snapshot. + */ + PushActiveSnapshot(GetTransactionSnapshot()); + object.classId = RelationRelationId; object.objectId = relid; object.objectSubId = 0; @@ -2246,6 +2252,7 @@ do_autovacuum(void) * To commit the deletion, end current transaction and start a new * one. Note this also releases the locks we took. */ + PopActiveSnapshot(); CommitTransactionCommand(); StartTransactionCommand(); diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c index 4151a4b2a96..a23262957ac 100644 --- a/src/backend/replication/logical/worker.c +++ b/src/backend/replication/logical/worker.c @@ -4626,8 +4626,16 @@ run_apply_worker() walrcv_startstreaming(LogRepWorkerWalRcvConn, &options); StartTransactionCommand(); + + /* + * Updating pg_subscription might involve TOAST table access, so + * ensure we have a valid snapshot. + */ + PushActiveSnapshot(GetTransactionSnapshot()); + UpdateTwoPhaseState(MySubscription->oid, LOGICALREP_TWOPHASE_STATE_ENABLED); MySubscription->twophasestate = LOGICALREP_TWOPHASE_STATE_ENABLED; + PopActiveSnapshot(); CommitTransactionCommand(); } else @@ -4843,7 +4851,15 @@ DisableSubscriptionAndExit(void) /* Disable the subscription */ StartTransactionCommand(); + + /* + * Updating pg_subscription might involve TOAST table access, so ensure we + * have a valid snapshot. + */ + PushActiveSnapshot(GetTransactionSnapshot()); + DisableSubscription(MySubscription->oid); + PopActiveSnapshot(); CommitTransactionCommand(); /* Ensure we remove no-longer-useful entry for worker's start time */ @@ -4947,6 +4963,12 @@ clear_subscription_skip_lsn(XLogRecPtr finish_lsn) started_tx = true; } + /* + * Updating pg_subscription might involve TOAST table access, so ensure we + * have a valid snapshot. + */ + PushActiveSnapshot(GetTransactionSnapshot()); + /* * Protect subskiplsn of pg_subscription from being concurrently updated * while clearing it. @@ -5005,6 +5027,8 @@ clear_subscription_skip_lsn(XLogRecPtr finish_lsn) heap_freetuple(tup); table_close(rel, NoLock); + PopActiveSnapshot(); + if (started_tx) CommitTransactionCommand(); } -- 2.39.5 (Apple Git-154)