From ee437ca7408b67f2b785e4221c7e567aecf68b47 Mon Sep 17 00:00:00 2001
From: Alexander Korotkov <akorotkov@postgresql.org>
Date: Tue, 19 Nov 2019 23:08:14 +0300
Subject: [PATCH] Fix traversing to the deleted GIN page via downlink

Current GIN code appears to don't handle traversing to the deleted page via
downlink.  This commit fixes that by stepping right from the delete page like
we do in nbtree.

This commit also fixes setting 'deleted' flag to the GIN pages.  Now other page
flags are not erased once page is deleted.  That helps to keep our assertions
true if we arrive deleted page via downlink.

Discussion: https://postgr.es/m/CAPpHfdvMvsw-NcE5bRS7R1BbvA4BxoDnVVjkXC5W0Czvy9LVrg%40mail.gmail.com
Author: Alexander Korotkov
Reviewed-by: Peter Geoghegan
Backpatch-through: 9.4
---
 src/backend/access/gin/ginbtree.c    | 7 -------
 src/backend/access/gin/gindatapage.c | 3 +++
 src/backend/access/gin/ginvacuum.c   | 2 +-
 src/backend/access/gin/ginxlog.c     | 2 +-
 4 files changed, 5 insertions(+), 9 deletions(-)

diff --git a/src/backend/access/gin/ginbtree.c b/src/backend/access/gin/ginbtree.c
index 11a8ed7bbc2..fde350eef13 100644
--- a/src/backend/access/gin/ginbtree.c
+++ b/src/backend/access/gin/ginbtree.c
@@ -187,13 +187,6 @@ ginStepRight(Buffer buffer, Relation index, int lockmode)
 	if (isLeaf != GinPageIsLeaf(page) || isData != GinPageIsData(page))
 		elog(ERROR, "right sibling of GIN page is of different type");
 
-	/*
-	 * Given the proper lock sequence above, we should never land on a deleted
-	 * page.
-	 */
-	if (GinPageIsDeleted(page))
-		elog(ERROR, "right sibling of GIN page was deleted");
-
 	return nextbuffer;
 }
 
diff --git a/src/backend/access/gin/gindatapage.c b/src/backend/access/gin/gindatapage.c
index 57c3b830d85..197aea3bd30 100644
--- a/src/backend/access/gin/gindatapage.c
+++ b/src/backend/access/gin/gindatapage.c
@@ -238,6 +238,9 @@ dataIsMoveRight(GinBtree btree, Page page)
 	if (GinPageRightMost(page))
 		return false;
 
+	if (GinPageIsDeleted(page))
+		return true;
+
 	return (ginCompareItemPointers(&btree->itemptr, iptr) > 0) ? true : false;
 }
 
diff --git a/src/backend/access/gin/ginvacuum.c b/src/backend/access/gin/ginvacuum.c
index 85acddc76b3..3a695a05552 100644
--- a/src/backend/access/gin/ginvacuum.c
+++ b/src/backend/access/gin/ginvacuum.c
@@ -186,7 +186,7 @@ ginDeletePage(GinVacuumState *gvs, BlockNumber deleteBlkno, BlockNumber leftBlkn
 	 * we shouldn't change rightlink field to save workability of running
 	 * search scan
 	 */
-	GinPageGetOpaque(page)->flags = GIN_DELETED;
+	GinPageSetDeleted(page);
 
 	MarkBufferDirty(pBuffer);
 	MarkBufferDirty(lBuffer);
diff --git a/src/backend/access/gin/ginxlog.c b/src/backend/access/gin/ginxlog.c
index c945b282721..387102f21a1 100644
--- a/src/backend/access/gin/ginxlog.c
+++ b/src/backend/access/gin/ginxlog.c
@@ -500,7 +500,7 @@ ginRedoDeletePage(XLogReaderState *record)
 	{
 		page = BufferGetPage(dbuffer);
 		Assert(GinPageIsData(page));
-		GinPageGetOpaque(page)->flags = GIN_DELETED;
+		GinPageSetDeleted(page);
 		GinPageSetDeleteXid(page, data->deleteXid);
 		PageSetLSN(page, lsn);
 		MarkBufferDirty(dbuffer);