Repair problems with VACUUM destroying t_ctid chains too soon, and with

insufficient paranoia in code that follows t_ctid links.  (We must do both
because even with VACUUM doing it properly, the intermediate state with
a dangling t_ctid link is visible concurrently during lazy VACUUM, and
could be seen afterwards if either type of VACUUM crashes partway through.)
Also try to improve documentation about what's going on.  Patch is a bit
bulky because passing the XMAX information around required changing the
APIs of some low-level heapam.c routines, but it's not conceptually very
complicated.  Per trouble report from Teodor and subsequent analysis.
This needs to be back-patched, but I'll do that after 8.1 beta is out.

1 files changed, 20 insertions, 12 deletions

diff --git a/src/backend/commands/trigger.c b/src/backend/commands/trigger.c
index 4ea973ae7fa..562f676f4b8 100644
--- a/src/backend/commands/trigger.c
+++ b/src/backend/commands/trigger.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.191 2005/08/12 01:35:57 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.192 2005/08/20 00:39:54 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1592,14 +1592,18 @@ GetTupleForTrigger(EState *estate, ResultRelInfo *relinfo,
 	if (newSlot != NULL)
 	{
 		HTSU_Result	test;
+		ItemPointerData update_ctid;
+		TransactionId update_xmax;
+
+		*newSlot = NULL;
 
 		/*
 		 * lock tuple for update
 		 */
-		*newSlot = NULL;
-		tuple.t_self = *tid;
 ltrmark:;
-		test = heap_lock_tuple(relation, &tuple, &buffer, cid,
+		tuple.t_self = *tid;
+		test = heap_lock_tuple(relation, &tuple, &buffer,
+							   &update_ctid, &update_xmax, cid,
 							   LockTupleExclusive, false);
 		switch (test)
 		{
@@ -1617,15 +1621,18 @@ ltrmark:;
 					ereport(ERROR,
 							(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
 							 errmsg("could not serialize access due to concurrent update")));
-				else if (!(ItemPointerEquals(&(tuple.t_self), tid)))
+				else if (!ItemPointerEquals(&update_ctid, &tuple.t_self))
 				{
-					TupleTableSlot *epqslot = EvalPlanQual(estate,
-											 relinfo->ri_RangeTableIndex,
-														&(tuple.t_self));
-
-					if (!(TupIsNull(epqslot)))
+					/* it was updated, so look at the updated version */
+					TupleTableSlot *epqslot;
+
+					epqslot = EvalPlanQual(estate,
+										   relinfo->ri_RangeTableIndex,
+										   &update_ctid,
+										   update_xmax);
+					if (!TupIsNull(epqslot))
 					{
-						*tid = tuple.t_self;
+						*tid = update_ctid;
 						*newSlot = epqslot;
 						goto ltrmark;
 					}
@@ -1639,7 +1646,7 @@ ltrmark:;
 
 			default:
 				ReleaseBuffer(buffer);
-				elog(ERROR, "invalid heap_lock_tuple status: %d", test);
+				elog(ERROR, "unrecognized heap_lock_tuple status: %u", test);
 				return NULL;	/* keep compiler quiet */
 		}
 	}
@@ -1659,6 +1666,7 @@ ltrmark:;
 		tuple.t_data = (HeapTupleHeader) PageGetItem((Page) dp, lp);
 		tuple.t_len = ItemIdGetLength(lp);
 		tuple.t_self = *tid;
+		tuple.t_tableOid = RelationGetRelid(relation);
 	}
 
 	result = heap_copytuple(&tuple);