Date: Tue, 29 Sep 2020 13:44:11 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Pg Hackers <pgsql-hackers@lists.postgresql.org>
Cc: Pavan Deolasee <pavan.deolasee@2ndQuadrant.com>,
	Andres Freund <andres@anarazel.de>
Subject: some pointless HeapTupleHeaderIndicatesMovedPartitions calls
Message-ID: <20200929164411.GA15497@alvherre.pgsql>
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Hello

Pavan Deolasee recently noted that a few of the
HeapTupleHeaderIndicatesMovedPartitions calls added by commit
5db6df0c0117 are useless, since they are done after comparing t_self
with t_ctid.  That's because t_self can never be set to the magical
values that indicate that the tuple moved partition.  If the first
test fails (so we know t_self equals t_ctid), necessarily the second
test will also fail.

So these checks can be removed and no harm is done.

-- 
Álvaro Herrera                            39°49'30"S 73°17'W

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 filename="0001-Remove-pointless-HeapTupleHeaderIndicatesMovedPartit.patch"

From 953eceb701ca35c5a3c731c4318ed1465f205811 Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: Tue, 29 Sep 2020 10:47:45 -0300
Subject: [PATCH] Remove pointless HeapTupleHeaderIndicatesMovedPartitions
 calls

---
 src/backend/access/heap/heapam.c            | 12 ++++--------
 src/backend/access/heap/heapam_visibility.c |  9 +++------
 2 files changed, 7 insertions(+), 14 deletions(-)

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 1585861a02..868ff13453 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -2618,8 +2618,7 @@ l1:
 			HEAP_XMAX_IS_LOCKED_ONLY(tp.t_data->t_infomask) ||
 			HeapTupleHeaderIsOnlyLocked(tp.t_data))
 			result = TM_Ok;
-		else if (!ItemPointerEquals(&tp.t_self, &tp.t_data->t_ctid) ||
-				 HeapTupleHeaderIndicatesMovedPartitions(tp.t_data))
+		else if (!ItemPointerEquals(&tp.t_self, &tp.t_data->t_ctid))
 			result = TM_Updated;
 		else
 			result = TM_Deleted;
@@ -3248,8 +3247,7 @@ l2:
 
 		if (can_continue)
 			result = TM_Ok;
-		else if (!ItemPointerEquals(&oldtup.t_self, &oldtup.t_data->t_ctid) ||
-				 HeapTupleHeaderIndicatesMovedPartitions(oldtup.t_data))
+		else if (!ItemPointerEquals(&oldtup.t_self, &oldtup.t_data->t_ctid))
 			result = TM_Updated;
 		else
 			result = TM_Deleted;
@@ -4485,8 +4483,7 @@ l3:
 			HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_data->t_infomask) ||
 			HeapTupleHeaderIsOnlyLocked(tuple->t_data))
 			result = TM_Ok;
-		else if (!ItemPointerEquals(&tuple->t_self, &tuple->t_data->t_ctid) ||
-				 HeapTupleHeaderIndicatesMovedPartitions(tuple->t_data))
+		else if (!ItemPointerEquals(&tuple->t_self, &tuple->t_data->t_ctid))
 			result = TM_Updated;
 		else
 			result = TM_Deleted;
@@ -5059,8 +5056,7 @@ test_lockmode_for_conflict(MultiXactStatus status, TransactionId xid,
 								LOCKMODE_from_mxstatus(wantedstatus)))
 		{
 			/* bummer */
-			if (!ItemPointerEquals(&tup->t_self, &tup->t_data->t_ctid) ||
-				HeapTupleHeaderIndicatesMovedPartitions(tup->t_data))
+			if (!ItemPointerEquals(&tup->t_self, &tup->t_data->t_ctid))
 				return TM_Updated;
 			else
 				return TM_Deleted;
diff --git a/src/backend/access/heap/heapam_visibility.c b/src/backend/access/heap/heapam_visibility.c
index 80bd494076..cab6a48a5d 100644
--- a/src/backend/access/heap/heapam_visibility.c
+++ b/src/backend/access/heap/heapam_visibility.c
@@ -607,8 +607,7 @@ HeapTupleSatisfiesUpdate(HeapTuple htup, CommandId curcid,
 	{
 		if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
 			return TM_Ok;
-		if (!ItemPointerEquals(&htup->t_self, &tuple->t_ctid) ||
-			HeapTupleHeaderIndicatesMovedPartitions(tuple))
+		if (!ItemPointerEquals(&htup->t_self, &tuple->t_ctid))
 			return TM_Updated;	/* updated by other */
 		else
 			return TM_Deleted;	/* deleted by other */
@@ -653,8 +652,7 @@ HeapTupleSatisfiesUpdate(HeapTuple htup, CommandId curcid,
 
 		if (TransactionIdDidCommit(xmax))
 		{
-			if (!ItemPointerEquals(&htup->t_self, &tuple->t_ctid) ||
-				HeapTupleHeaderIndicatesMovedPartitions(tuple))
+			if (!ItemPointerEquals(&htup->t_self, &tuple->t_ctid))
 				return TM_Updated;
 			else
 				return TM_Deleted;
@@ -714,8 +712,7 @@ HeapTupleSatisfiesUpdate(HeapTuple htup, CommandId curcid,
 
 	SetHintBits(tuple, buffer, HEAP_XMAX_COMMITTED,
 				HeapTupleHeaderGetRawXmax(tuple));
-	if (!ItemPointerEquals(&htup->t_self, &tuple->t_ctid) ||
-		HeapTupleHeaderIndicatesMovedPartitions(tuple))
+	if (!ItemPointerEquals(&htup->t_self, &tuple->t_ctid))
 		return TM_Updated;		/* updated by other */
 	else
 		return TM_Deleted;		/* deleted by other */
-- 
2.20.1


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