From 6b8e0a610556cc01680b30c683562772922dc00d Mon Sep 17 00:00:00 2001
From: Nils Dijk <nils@citusdata.com>
Date: Thu, 7 May 2020 19:08:47 +0200
Subject: [PATCH] fix subtle bug in adding to a list we are iterating over

---
 .../distributed/planner/path_based_planner.c      | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/src/backend/distributed/planner/path_based_planner.c b/src/backend/distributed/planner/path_based_planner.c
index 5cbd58ada..8dad7612e 100644
--- a/src/backend/distributed/planner/path_based_planner.c
+++ b/src/backend/distributed/planner/path_based_planner.c
@@ -383,6 +383,13 @@ PathBasedPlannerJoinHook(PlannerInfo *root,
 						 JoinType jointype,
 						 JoinPathExtraData *extra)
 {
+	/*
+	 * Adding a path to a list includes lappend which might be destructive. Since we are
+	 * looping over the paths we are adding to we should keep a list of new paths to add
+	 * and only add them after we have found all the paths we want to add.
+	 */
+	List *newPaths = NIL;
+
 	if (jointype == JOIN_INNER)
 	{
 		ListCell *pathCell = NULL;
@@ -392,10 +399,16 @@ PathBasedPlannerJoinHook(PlannerInfo *root,
 			Path *optimizedPath = OptimizeJoinPath(originalPath);
 			if (optimizedPath)
 			{
-				add_path(joinrel, optimizedPath);
+				newPaths = lappend(newPaths, optimizedPath);
 			}
 		}
 	}
+
+	Path *path = NULL;
+	foreach_ptr(path, newPaths)
+	{
+		add_path(joinrel, path);
+	}
 }
 
 /*