From a49633d8dc6c66f6b2e92c8598d3dfa2cc72a259 Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Fri, 13 Dec 2013 13:52:47 +0200
Subject: [PATCH] Fix WAL-logging of setting the visibility map bit.

The operation that removes the remaining dead tuples from the page must
be WAL-logged before the setting of the VM bit. Otherwise, if you replay
the WAL to between those two records, you end up with the VM bit set, but
the dead tuples are still there.

Backpatch to 9.3, where this bug was introduced.
---
 src/backend/commands/vacuumlazy.c | 27 ++++++++++++---------------
 1 file changed, 12 insertions(+), 15 deletions(-)

diff --git a/src/backend/commands/vacuumlazy.c b/src/backend/commands/vacuumlazy.c
index 7b9837f4f4..28e98e8b48 100644
--- a/src/backend/commands/vacuumlazy.c
+++ b/src/backend/commands/vacuumlazy.c
@@ -1182,12 +1182,21 @@ lazy_vacuum_page(Relation onerel, BlockNumber blkno, Buffer buffer,
 
 	/*
 	 * Mark buffer dirty before we write WAL.
-	 *
-	 * If checksums are enabled, visibilitymap_set() may log the heap page, so
-	 * we must mark heap buffer dirty before calling visibilitymap_set().
 	 */
 	MarkBufferDirty(buffer);
 
+	/* XLOG stuff */
+	if (RelationNeedsWAL(onerel))
+	{
+		XLogRecPtr	recptr;
+
+		recptr = log_heap_clean(onerel, buffer,
+								NULL, 0, NULL, 0,
+								unused, uncnt,
+								vacrelstats->latestRemovedXid);
+		PageSetLSN(page, recptr);
+	}
+
 	/*
 	 * Now that we have removed the dead tuples from the page, once again
 	 * check if the page has become all-visible.
@@ -1201,18 +1210,6 @@ lazy_vacuum_page(Relation onerel, BlockNumber blkno, Buffer buffer,
 						  visibility_cutoff_xid);
 	}
 
-	/* XLOG stuff */
-	if (RelationNeedsWAL(onerel))
-	{
-		XLogRecPtr	recptr;
-
-		recptr = log_heap_clean(onerel, buffer,
-								NULL, 0, NULL, 0,
-								unused, uncnt,
-								vacrelstats->latestRemovedXid);
-		PageSetLSN(page, recptr);
-	}
-
 	END_CRIT_SECTION();
 
 	return tupindex;