Don't TransactionIdDidAbort in HeapTupleGetUpdateXid

It is dangerous to do so, because some code expects to be able to see what's
the true Xmax even if it is aborted (particularly while traversing HOT
chains).  So don't do it, and instead rely on the callers to verify for
abortedness, if necessary.

Several race conditions and bugs fixed in the process.  One isolation test
changes the expected output due to these.

This also reverts commit c235a6a589, which is no longer necessary.

Backpatch to 9.3, where this function was introduced.

Andres Freund

src/backend/access/heap/heapam.c

@@ -3164,7 +3164,11 @@ l2:
 			if (!HEAP_XMAX_IS_LOCKED_ONLY(oldtup.t_data->t_infomask))
 				update_xact = HeapTupleGetUpdateXid(oldtup.t_data);
 
-			/* there was no UPDATE in the MultiXact; or it aborted. */
+			/*
+			 * There was no UPDATE in the MultiXact; or it aborted. No
+			 * TransactionIdIsInProgress() call needed here, since we called
+			 * MultiXactIdWait() above.
+			 */
 			if (!TransactionIdIsValid(update_xact) ||
 				TransactionIdDidAbort(update_xact))
 				can_continue = true;
@@ -5424,6 +5428,9 @@ GetMultiXactIdHintBits(MultiXactId multi, uint16 *new_infomask,
  * Given a multixact Xmax and corresponding infomask, which does not have the
  * HEAP_XMAX_LOCK_ONLY bit set, obtain and return the Xid of the updating
  * transaction.
+ *
+ * Caller is expected to check the status of the updating transaction, if
+ * necessary.
  */
 static TransactionId
 MultiXactIdGetUpdateXid(TransactionId xmax, uint16 t_infomask)
@@ -5448,19 +5455,11 @@ MultiXactIdGetUpdateXid(TransactionId xmax, uint16 t_infomask)
 		for (i = 0; i < nmembers; i++)
 		{
 			/* Ignore lockers */
-			if (members[i].status == MultiXactStatusForKeyShare ||
+			if (!ISUPDATE_from_mxstatus(members[i].status))
-				members[i].status == MultiXactStatusForShare ||
-				members[i].status == MultiXactStatusForNoKeyUpdate ||
-				members[i].status == MultiXactStatusForUpdate)
 				continue;
 
-			/* ignore aborted transactions */
+			/* there can be at most one updater */
-			if (TransactionIdDidAbort(members[i].xid))
-				continue;
-			/* there should be at most one non-aborted updater */
 			Assert(update_xact == InvalidTransactionId);
-			Assert(members[i].status == MultiXactStatusNoKeyUpdate ||
-				   members[i].status == MultiXactStatusUpdate);
 			update_xact = members[i].xid;
 #ifndef USE_ASSERT_CHECKING
 

src/backend/access/heap/pruneheap.c

@@ -466,22 +466,12 @@ heap_prune_chain(Relation relation, Buffer buffer, OffsetNumber rootoffnum,
 				break;
 
 			case HEAPTUPLE_DELETE_IN_PROGRESS:
-				{
+				/*
-					TransactionId	xmax;
+				 * This tuple may soon become DEAD.  Update the hint field
-
+				 * so that the page is reconsidered for pruning in future.
-					/*
+				 */
-					 * This tuple may soon become DEAD.  Update the hint field
+				heap_prune_record_prunable(prstate,
-					 * so that the page is reconsidered for pruning in future.
+										   HeapTupleHeaderGetUpdateXid(htup));
-					 * If there was a MultiXactId updater, and it aborted after
-					 * HTSV checked, then we will get an invalid Xid here.
-					 * There is no need for future pruning of the page in that
-					 * case, so skip it.
-					 */
-					xmax = HeapTupleHeaderGetUpdateXid(htup);
-					if (TransactionIdIsValid(xmax))
-						heap_prune_record_prunable(prstate, xmax);
-				}
-
 				break;
 
 			case HEAPTUPLE_LIVE:

src/backend/utils/time/tqual.c

@@ -222,8 +222,9 @@ HeapTupleSatisfiesSelf(HeapTupleHeader tuple, Snapshot snapshot, Buffer buffer)
 				TransactionId xmax;
 
 				xmax = HeapTupleGetUpdateXid(tuple);
-				if (!TransactionIdIsValid(xmax))
+
-					return true;
+				/* not LOCKED_ONLY, so it has to have an xmax */
+				Assert(TransactionIdIsValid(xmax));
 
 				/* updating subtransaction must have aborted */
 				if (!TransactionIdIsCurrentTransactionId(xmax))
@@ -276,14 +277,17 @@ HeapTupleSatisfiesSelf(HeapTupleHeader tuple, Snapshot snapshot, Buffer buffer)
 			return true;
 
 		xmax = HeapTupleGetUpdateXid(tuple);
-		if (!TransactionIdIsValid(xmax))
+
-			return true;
+		/* not LOCKED_ONLY, so it has to have an xmax */
+		Assert(TransactionIdIsValid(xmax));
+
 		if (TransactionIdIsCurrentTransactionId(xmax))
 			return false;
 		if (TransactionIdIsInProgress(xmax))
 			return true;
 		if (TransactionIdDidCommit(xmax))
 			return false;
+		/* it must have aborted or crashed */
 		return true;
 	}
 
@@ -690,8 +694,9 @@ HeapTupleSatisfiesUpdate(HeapTupleHeader tuple, CommandId curcid,
 				TransactionId xmax;
 
 				xmax = HeapTupleGetUpdateXid(tuple);
-				if (!TransactionIdIsValid(xmax))
+
-					return HeapTupleMayBeUpdated;
+				/* not LOCKED_ONLY, so it has to have an xmax */
+				Assert(TransactionIdIsValid(xmax));
 
 				/* updating subtransaction must have aborted */
 				if (!TransactionIdIsCurrentTransactionId(xmax))
@@ -766,14 +771,9 @@ HeapTupleSatisfiesUpdate(HeapTupleHeader tuple, CommandId curcid,
 		}
 
 		xmax = HeapTupleGetUpdateXid(tuple);
-		if (!TransactionIdIsValid(xmax))
-		{
-			if (MultiXactIdIsRunning(HeapTupleHeaderGetRawXmax(tuple)))
-				return HeapTupleBeingUpdated;
 
-			SetHintBits(tuple, buffer, HEAP_XMAX_INVALID, InvalidTransactionId);
+		/* not LOCKED_ONLY, so it has to have an xmax */
-			return HeapTupleMayBeUpdated;
+		Assert(TransactionIdIsValid(xmax));
-		}
 
 		if (TransactionIdIsCurrentTransactionId(xmax))
 		{
@@ -783,13 +783,18 @@ HeapTupleSatisfiesUpdate(HeapTupleHeader tuple, CommandId curcid,
 				return HeapTupleInvisible;		/* updated before scan started */
 		}
 
-		if (MultiXactIdIsRunning(HeapTupleHeaderGetRawXmax(tuple)))
+		if (TransactionIdIsInProgress(xmax))
 			return HeapTupleBeingUpdated;
 
 		if (TransactionIdDidCommit(xmax))
 			return HeapTupleUpdated;
+
+		/* no member, even just a locker, alive anymore */
+		if (!MultiXactIdIsRunning(HeapTupleHeaderGetRawXmax(tuple)))
+			SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
+						InvalidTransactionId);
+
 		/* it must have aborted or crashed */
-		SetHintBits(tuple, buffer, HEAP_XMAX_INVALID, InvalidTransactionId);
 		return HeapTupleMayBeUpdated;
 	}
 
@@ -911,8 +916,9 @@ HeapTupleSatisfiesDirty(HeapTupleHeader tuple, Snapshot snapshot,
 				TransactionId xmax;
 
 				xmax = HeapTupleGetUpdateXid(tuple);
-				if (!TransactionIdIsValid(xmax))
+
-					return true;
+				/* not LOCKED_ONLY, so it has to have an xmax */
+				Assert(TransactionIdIsValid(xmax));
 
 				/* updating subtransaction must have aborted */
 				if (!TransactionIdIsCurrentTransactionId(xmax))
@@ -969,8 +975,10 @@ HeapTupleSatisfiesDirty(HeapTupleHeader tuple, Snapshot snapshot,
 			return true;
 
 		xmax = HeapTupleGetUpdateXid(tuple);
-		if (!TransactionIdIsValid(xmax))
+
-			return true;
+		/* not LOCKED_ONLY, so it has to have an xmax */
+		Assert(TransactionIdIsValid(xmax));
+
 		if (TransactionIdIsCurrentTransactionId(xmax))
 			return false;
 		if (TransactionIdIsInProgress(xmax))
@@ -980,6 +988,7 @@ HeapTupleSatisfiesDirty(HeapTupleHeader tuple, Snapshot snapshot,
 		}
 		if (TransactionIdDidCommit(xmax))
 			return false;
+		/* it must have aborted or crashed */
 		return true;
 	}
 
@@ -1104,8 +1113,9 @@ HeapTupleSatisfiesMVCC(HeapTupleHeader tuple, Snapshot snapshot,
 				TransactionId xmax;
 
 				xmax = HeapTupleGetUpdateXid(tuple);
-				if (!TransactionIdIsValid(xmax))
+
-					return true;
+				/* not LOCKED_ONLY, so it has to have an xmax */
+				Assert(TransactionIdIsValid(xmax));
 
 				/* updating subtransaction must have aborted */
 				if (!TransactionIdIsCurrentTransactionId(xmax))
@@ -1164,8 +1174,10 @@ HeapTupleSatisfiesMVCC(HeapTupleHeader tuple, Snapshot snapshot,
 		Assert(!HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask));
 
 		xmax = HeapTupleGetUpdateXid(tuple);
-		if (!TransactionIdIsValid(xmax))
+
-			return true;
+		/* not LOCKED_ONLY, so it has to have an xmax */
+		Assert(TransactionIdIsValid(xmax));
+
 		if (TransactionIdIsCurrentTransactionId(xmax))
 		{
 			if (HeapTupleHeaderGetCmax(tuple) >= snapshot->curcid)
@@ -1182,6 +1194,7 @@ HeapTupleSatisfiesMVCC(HeapTupleHeader tuple, Snapshot snapshot,
 				return true;	/* treat as still in progress */
 			return false;
 		}
+		/* it must have aborted or crashed */
 		return true;
 	}
 
@@ -1376,8 +1389,10 @@ HeapTupleSatisfiesVacuum(HeapTupleHeader tuple, TransactionId OldestXmin,
 			Assert(!HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask));
 
 			xmax = HeapTupleGetUpdateXid(tuple);
-			if (!TransactionIdIsValid(xmax))
+
-				return HEAPTUPLE_LIVE;
+			/* not LOCKED_ONLY, so it has to have an xmax */
+			Assert(TransactionIdIsValid(xmax));
+
 			if (TransactionIdIsInProgress(xmax))
 				return HEAPTUPLE_DELETE_IN_PROGRESS;
 			else if (TransactionIdDidCommit(xmax))
@@ -1390,8 +1405,10 @@ HeapTupleSatisfiesVacuum(HeapTupleHeader tuple, TransactionId OldestXmin,
 		Assert(!(tuple->t_infomask & HEAP_XMAX_COMMITTED));
 
 		xmax = HeapTupleGetUpdateXid(tuple);
-		if (!TransactionIdIsValid(xmax))
+
-			return HEAPTUPLE_LIVE;
+		/* not LOCKED_ONLY, so it has to have an xmax */
+		Assert(TransactionIdIsValid(xmax));
+
 		/* multi is not running -- updating xact cannot be */
 		Assert(!TransactionIdIsInProgress(xmax));
 		if (TransactionIdDidCommit(xmax))
@@ -1401,22 +1418,13 @@ HeapTupleSatisfiesVacuum(HeapTupleHeader tuple, TransactionId OldestXmin,
 			else
 				return HEAPTUPLE_DEAD;
 		}
-		else
-		{
-			/*
-			 * Not in Progress, Not Committed, so either Aborted or crashed.
-			 */
-			SetHintBits(tuple, buffer, HEAP_XMAX_INVALID, InvalidTransactionId);
-			return HEAPTUPLE_LIVE;
-		}
 
 		/*
-		 * Deleter committed, but perhaps it was recent enough that some open
+		 * Not in Progress, Not Committed, so either Aborted or crashed.
-		 * transactions could still see the tuple.
+		 * Remove the Xmax.
 		 */
-
+		SetHintBits(tuple, buffer, HEAP_XMAX_INVALID, InvalidTransactionId);
-		/* Otherwise, it's dead and removable */
+		return HEAPTUPLE_LIVE;
-		return HEAPTUPLE_DEAD;
 	}
 
 	if (!(tuple->t_infomask & HEAP_XMAX_COMMITTED))
@@ -1655,8 +1663,9 @@ HeapTupleHeaderIsOnlyLocked(HeapTupleHeader tuple)
 
 	/* ... but if it's a multi, then perhaps the updating Xid aborted. */
 	xmax = HeapTupleGetUpdateXid(tuple);
-	if (!TransactionIdIsValid(xmax))	/* shouldn't happen .. */
+
-		return true;
+	/* not LOCKED_ONLY, so it has to have an xmax */
+	Assert(TransactionIdIsValid(xmax));
 
 	if (TransactionIdIsCurrentTransactionId(xmax))
 		return false;

src/test/isolation/expected/delete-abort-savept.out

@@ -23,12 +23,11 @@ key            value
 step s1svp: SAVEPOINT f;
 step s1d: DELETE FROM foo;
 step s1r: ROLLBACK TO f;
-step s2l: SELECT * FROM foo FOR UPDATE; <waiting ...>
+step s2l: SELECT * FROM foo FOR UPDATE;
-step s1c: COMMIT;
-step s2l: <... completed>
 key            value          
 
 1              1              
+step s1c: COMMIT;
 step s2c: COMMIT;
 
 starting permutation: s1l s1svp s1d s1r s2l s2c s1c
@@ -39,8 +38,12 @@ key            value
 step s1svp: SAVEPOINT f;
 step s1d: DELETE FROM foo;
 step s1r: ROLLBACK TO f;
-step s2l: SELECT * FROM foo FOR UPDATE; <waiting ...>
+step s2l: SELECT * FROM foo FOR UPDATE;
-invalid permutation detected
+key            value          
+
+1              1              
+step s2c: COMMIT;
+step s1c: COMMIT;
 
 starting permutation: s1l s1svp s1d s2l s1r s1c s2c
 step s1l: SELECT * FROM foo FOR KEY SHARE;