From e7542220d25fad39b753969296510893c9f9915d Mon Sep 17 00:00:00 2001
From: Tomas Vondra <tomas@2ndquadrant.com>
Date: Sun, 29 Jan 2017 19:15:29 +0100
Subject: [PATCH] fix handling of inner/outer sortkeys in
 set_joinpath_distribution()

We must not reset inner/outer sortkeys unless the path is actually
redistributed. When a redistribution is not needed, the merge join
needs the original values. Otherwise this results in errors like

    ERROR: inner pathkeys do not match mergeclauses
    ERROR: outer pathkeys do not match mergeclauses
---
 src/backend/optimizer/util/pathnode.c | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
index 4077b8770b..c0ff99829c 100644
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -1974,6 +1974,9 @@ not_allowed_join:
 						(Node *) new_inner_key,
 						nodes,
 						restrictNodes);
+
+				if (IsA(pathnode, MergePath))
+					((MergePath*)pathnode)->innersortkeys = NIL;
 			}
 			/*
 			 * Redistribute join by hash, and, if jointype allows, create
@@ -1990,6 +1993,9 @@ not_allowed_join:
 						(Node *) new_outer_key,
 						nodes,
 						restrictNodes);
+
+				if (IsA(pathnode, MergePath))
+					((MergePath*)pathnode)->outersortkeys = NIL;
 			}
 			targetd = makeNode(Distribution);
 			targetd->distributionType = distType;
@@ -2005,8 +2011,8 @@ not_allowed_join:
 			 */
 			if (IsA(pathnode, MergePath))
 			{
-				((MergePath*)pathnode)->innersortkeys = NIL;
-				((MergePath*)pathnode)->outersortkeys = NIL;
+				// ((MergePath*)pathnode)->innersortkeys = NIL;
+				// ((MergePath*)pathnode)->outersortkeys = NIL;
 			}
 
 			/*
@@ -2040,6 +2046,7 @@ not_allowed_join:
 	 * relations.
 	 */
 	if (innerd)
+	{
 		pathnode->innerjoinpath = redistribute_path(root,
 													pathnode->innerjoinpath,
 													innerpathkeys,
@@ -2047,7 +2054,13 @@ not_allowed_join:
 													NULL,
 													NULL,
 													NULL);
+
+		if (IsA(pathnode, MergePath))
+			((MergePath*)pathnode)->innersortkeys = NIL;
+	}
+
 	if (outerd)
+	{
 		pathnode->outerjoinpath = redistribute_path(root,
 													pathnode->outerjoinpath,
 													outerpathkeys,
@@ -2055,6 +2068,12 @@ not_allowed_join:
 													NULL,
 													NULL,
 													NULL);
+													
+
+		if (IsA(pathnode, MergePath))
+			((MergePath*)pathnode)->outersortkeys = NIL;
+	}
+
 	return alternate;
 }
 #endif
-- 
2.39.5