From 6da44715c992718782aa634e16df10ee1fe7ecdf Mon Sep 17 00:00:00 2001
From: tt <tt>
Date: Wed, 1 Apr 2020 18:08:52 +0200
Subject: [PATCH 7/7] extra patch

---
 src/backend/optimizer/path/allpaths.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index 4a72dcf8bc..0534bb24c5 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -2757,7 +2757,7 @@ get_useful_pathkeys_for_relation(PlannerInfo *root, RelOptInfo *rel)
 	if (root->query_pathkeys)
 	{
 		ListCell   *lc;
-		List	   *pathkeys = NIL;
+		int		npathkeys = 0;	/* useful pathkeys */
 
 		foreach(lc, root->query_pathkeys)
 		{
@@ -2778,11 +2778,21 @@ get_useful_pathkeys_for_relation(PlannerInfo *root, RelOptInfo *rel)
 			if (!find_em_expr_for_rel(pathkey_ec, rel))
 				break;
 
-			pathkeys = lappend(pathkeys, pathkey);
+			npathkeys++;
 		}
 
-		if (pathkeys)
-			useful_pathkeys_list = lappend(useful_pathkeys_list, pathkeys);
+		/*
+		 * The whole query_pathkeys list matches, so append it directly, to allow
+		 * comparing pathkeys easily by comparing list pointer. If we have to truncate
+		 * the pathkeys, we gotta do a copy though.
+		 */
+		if (npathkeys == list_length(root->query_pathkeys))
+			useful_pathkeys_list = lappend(useful_pathkeys_list,
+										   root->query_pathkeys);
+		else if (npathkeys > 0)
+			useful_pathkeys_list = lappend(useful_pathkeys_list,
+										   list_truncate(list_copy(root->query_pathkeys),
+														 npathkeys));
 	}
 
 	return useful_pathkeys_list;
-- 
2.24.1