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 c235a6a589b, which is no longer necessary.

Backpatch to 9.3, where this function was introduced.

Andres Freund

1 files changed, 51 insertions, 42 deletions

diff --git a/src/backend/utils/time/tqual.c b/src/backend/utils/time/tqual.c
index ed66c49a91f..1ebc5ff8795 100644
--- a/src/backend/utils/time/tqual.c
+++ b/src/backend/utils/time/tqual.c
@@ -223,8 +223,9 @@ HeapTupleSatisfiesSelf(HeapTuple htup, 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))
@@ -277,14 +278,17 @@ HeapTupleSatisfiesSelf(HeapTuple htup, 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;
 	}
 
@@ -497,8 +501,9 @@ HeapTupleSatisfiesUpdate(HeapTuple htup, 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))
@@ -573,14 +578,9 @@ HeapTupleSatisfiesUpdate(HeapTuple htup, CommandId curcid,
 		}
 
 		xmax = HeapTupleGetUpdateXid(tuple);
-		if (!TransactionIdIsValid(xmax))
-		{
-			if (MultiXactIdIsRunning(HeapTupleHeaderGetRawXmax(tuple)))
-				return HeapTupleBeingUpdated;
 
-			SetHintBits(tuple, buffer, HEAP_XMAX_INVALID, InvalidTransactionId);
-			return HeapTupleMayBeUpdated;
-		}
+		/* not LOCKED_ONLY, so it has to have an xmax */
+		Assert(TransactionIdIsValid(xmax));
 
 		if (TransactionIdIsCurrentTransactionId(xmax))
 		{
@@ -590,13 +590,18 @@ HeapTupleSatisfiesUpdate(HeapTuple htup, 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;
 	}
 
@@ -722,8 +727,9 @@ HeapTupleSatisfiesDirty(HeapTuple htup, 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))
@@ -780,8 +786,10 @@ HeapTupleSatisfiesDirty(HeapTuple htup, 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))
@@ -791,6 +799,7 @@ HeapTupleSatisfiesDirty(HeapTuple htup, Snapshot snapshot,
 		}
 		if (TransactionIdDidCommit(xmax))
 			return false;
+		/* it must have aborted or crashed */
 		return true;
 	}
 
@@ -915,8 +924,9 @@ HeapTupleSatisfiesMVCC(HeapTuple htup, 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))
@@ -975,8 +985,10 @@ HeapTupleSatisfiesMVCC(HeapTuple htup, 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)
@@ -993,6 +1005,7 @@ HeapTupleSatisfiesMVCC(HeapTuple htup, Snapshot snapshot,
 				return true;	/* treat as still in progress */
 			return false;
 		}
+		/* it must have aborted or crashed */
 		return true;
 	}
 
@@ -1191,8 +1204,10 @@ HeapTupleSatisfiesVacuum(HeapTuple htup, 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))
@@ -1205,8 +1220,10 @@ HeapTupleSatisfiesVacuum(HeapTuple htup, 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))
@@ -1216,22 +1233,13 @@ HeapTupleSatisfiesVacuum(HeapTuple htup, 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
-		 * transactions could still see the tuple.
+		 * Not in Progress, Not Committed, so either Aborted or crashed.
+		 * Remove the Xmax.
 		 */
-
-		/* Otherwise, it's dead and removable */
-		return HEAPTUPLE_DEAD;
+		SetHintBits(tuple, buffer, HEAP_XMAX_INVALID, InvalidTransactionId);
+		return HEAPTUPLE_LIVE;
 	}
 
 	if (!(tuple->t_infomask & HEAP_XMAX_COMMITTED))
@@ -1474,8 +1482,9 @@ 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;