0001-Fix-misleading-comment-in-nodeIndexonlyscan.c.patch

From 3097e1b7973e83b7ce05e5c81e3696852c0a7806 Mon Sep 17 00:00:00 2001
From: Thomas Munro <tmunro@postgresql.org>
Date: Fri, 28 Jun 2019 11:11:26 +1200
Subject: [PATCH] Fix misleading comment in nodeIndexonlyscan.c.

The stated reason for acquiring predicate locks on heap pages hasn't
existed since commit c01262a8, so fix the comment.  Perhaps in a later
release we'll also be able to change the code to use tuple locks.

Back-patch all the way.

Discussion: https://postgr.es/m/CAEepm%3D2GK3FVdnt5V3d%2Bh9njWipCv_fNL%3DwjxyUhzsF%3D0PcbNg%40mail.gmail.com
---
 src/backend/executor/nodeIndexonlyscan.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/src/backend/executor/nodeIndexonlyscan.c b/src/backend/executor/nodeIndexonlyscan.c
index 8a4d795d1a..f0f8fa210b 100644
--- a/src/backend/executor/nodeIndexonlyscan.c
+++ b/src/backend/executor/nodeIndexonlyscan.c
@@ -242,11 +242,8 @@ IndexOnlyNext(IndexOnlyScanState *node)
 					 errmsg("lossy distance functions are not supported in index-only scans")));
 
 		/*
-		 * Predicate locks for index-only scans must be acquired at the page
-		 * level when the heap is not accessed, since tuple-level predicate
-		 * locks need the tuple's xmin value.  If we had to visit the tuple
-		 * anyway, then we already have the tuple-level lock and can skip the
-		 * page lock.
+		 * If we didn't access the heap, then we'll need to take a predicate
+		 * lock explicitly, as if we had.  For now we do that at page level.
 		 */
 		if (!tuple_from_heap)
 			PredicateLockPage(scandesc->heapRelation,
-- 
2.21.0