v3-0002-Optimize-PredicateLockTuple.patch

From e73abc40fc6bbc087bbcaa109ef6c5b2fe642853 Mon Sep 17 00:00:00 2001
From: Ashwin Agrawal <aagrawal@pivotal.io>
Date: Fri, 2 Aug 2019 15:21:16 -0700
Subject: [PATCH v3 2/3] Optimize PredicateLockTuple().

PredicateLockTuple() has a fast exit if tuple was written by current
transaction, as for that case it already has a lock.  This check can
be performed using TransactionIdIsCurrentTransactionId() instead of
using SubTransGetTopmostTransaction().  Since
TransactionIdIsCurrentTransactionId() is an all-in-memory operation,
it makes this efficient compared to SubTransGetTopmostTransaction(),
which can hit the disk.

This simplification was proposed by Andres Freund.

Author: Ashwin Agrawal
Reviewed-by: Thomas Munro
Discussion: https://postgr.es/m/CALfoeiv0k3hkEb3Oqk%3DziWqtyk2Jys1UOK5hwRBNeANT_yX%2Bng%40mail.gmail.com
---
 src/backend/storage/lmgr/predicate.c | 21 +++------------------
 1 file changed, 3 insertions(+), 18 deletions(-)

diff --git a/src/backend/storage/lmgr/predicate.c b/src/backend/storage/lmgr/predicate.c
index 78fb90fb1b..d5468b3e29 100644
--- a/src/backend/storage/lmgr/predicate.c
+++ b/src/backend/storage/lmgr/predicate.c
@@ -2559,24 +2559,9 @@ PredicateLockTuple(Relation relation, HeapTuple tuple, Snapshot snapshot)
 	 */
 	if (relation->rd_index == NULL)
 	{
-		TransactionId myxid;
-
-		targetxmin = HeapTupleHeaderGetXmin(tuple->t_data);
-
-		myxid = GetTopTransactionIdIfAny();
-		if (TransactionIdIsValid(myxid))
-		{
-			if (TransactionIdFollowsOrEquals(targetxmin, TransactionXmin))
-			{
-				TransactionId xid = SubTransGetTopmostTransaction(targetxmin);
-
-				if (TransactionIdEquals(xid, myxid))
-				{
-					/* We wrote it; we already have a write lock. */
-					return;
-				}
-			}
-		}
+		/* If we wrote it; we already have a write lock. */
+		if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetXmin(tuple->t_data)))
+			return;
 	}
 
 	/*
-- 
2.23.0