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, fixing older versions doesn't seem
worth the trouble of significantly modifying the patch.

Also, on v13 and v14, the aforementioned strict assertions have
been omitted because commit 2776922201, which added
HaveRegisteredOrActiveSnapshot(), was not back-patched.  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 <exclusion@gmail.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
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

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 95e3be524a7f8c2528d0c6273ae6bb17c5375228..ccf151f548b463a655e09af48aec51e317b18770 100644 (file)
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -53,6 +53,7 @@
 #include "catalog/catalog.h"
 #include "catalog/pg_database.h"
 #include "catalog/pg_database_d.h"
+#include "catalog/pg_replication_origin.h"
 #include "commands/vacuum.h"
 #include "miscadmin.h"
 #include "pgstat.h"
@@ -230,6 +231,38 @@ 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;
+
+       /*
+        * Commit 16bf24e fixed accesses to pg_replication_origin without a
+        * an active snapshot by removing its TOAST table.  On older branches,
+        * these bugs are left in place.  Its only varlena column is roname (the
+        * replication origin name), so this is only a problem if the name
+        * requires out-of-line storage, which seems unlikely.  In any case,
+        * fixing it doesn't seem worth extra code churn on the back-branches.
+        */
+       if (RelationGetRelid(rel) == ReplicationOriginRelationId)
+               return;
+
+       Assert(HaveRegisteredOrActiveSnapshot());
+
+#endif                                                 /* USE_ASSERT_CHECKING */
+}
+
 /* ----------------------------------------------------------------
  *                                              heap support routines
  * ----------------------------------------------------------------
@@ -2015,6 +2048,8 @@ 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.
         *
@@ -2292,6 +2327,8 @@ 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);
@@ -2714,6 +2751,8 @@ 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
@@ -3209,6 +3248,8 @@ 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 f7fe1fae91c19e3824f76fece8a2ecd49681b337..08a056bc0f84b854b9a09278c1b7492cd930823b 100644 (file)
--- a/src/backend/commands/indexcmds.c
+++ b/src/backend/commands/indexcmds.c
@@ -4094,12 +4094,20 @@ ReindexRelationConcurrently(const ReindexStmt *stmt, Oid relationOid, const Rein
                                                                         get_rel_namespace(oldidx->tableId),
                                                                         false);
 
+               /*
+                * Swapping the indexes might involve TOAST table access, so ensure we
+                * have a valid snapshot.
+                */
+               PushActiveSnapshot(GetTransactionSnapshot());
+
                /*
                 * Swap old index with the new one.  This also marks the new one as
                 * valid and the old one as not valid.
                 */
                index_concurrently_swap(newidx->indexId, oldidx->indexId, oldName);
 
+               PopActiveSnapshot();
+
                /*
                 * Invalidate the relcache for the table, so that after this commit
                 * all sessions will refresh any cached plans that might reference the

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index e6606e5e57a4cb998fc1a20b7dd982bc147ed712..a4e0fd0678118bc5e868a62794acee8989907ff3 100644 (file)
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -19268,9 +19268,17 @@ 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 0e30a7fda66b5ec76e7f72969ae60b758cf9d347..ec5699e48e88410305129e84304392d8434e6811 100644 (file)
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -2220,6 +2220,12 @@ 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;
@@ -2232,6 +2238,7 @@ 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 db09978697f39b3345ba6e3c4628818b63809a71..1bff6c92dda0c0238cbdd4087449f307bb47c294 100644 (file)
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -4550,8 +4550,16 @@ 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
@@ -4767,7 +4775,15 @@ 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 */
@@ -4871,6 +4887,12 @@ 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.
@@ -4929,6 +4951,8 @@ clear_subscription_skip_lsn(XLogRecPtr finish_lsn)
        heap_freetuple(tup);
        table_close(rel, NoLock);
 
+       PopActiveSnapshot();
+
        if (started_tx)
                CommitTransactionCommand();
 }