From ca04790c276d1b97e19bd635b8221f9be1b6be59 Mon Sep 17 00:00:00 2001
From: Robert Haas <rhaas@postgresql.org>
Date: Thu, 22 Oct 2015 10:33:40 -0400
Subject: [PATCH] Test code.

---
 src/backend/access/transam/parallel.c |  2 ++
 src/backend/commands/explain.c        | 11 +++++++++++
 src/backend/optimizer/plan/planner.c  |  9 ++++++++-
 3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/src/backend/access/transam/parallel.c b/src/backend/access/transam/parallel.c
index 171356f3d5..fa0cb86e49 100644
--- a/src/backend/access/transam/parallel.c
+++ b/src/backend/access/transam/parallel.c
@@ -1080,7 +1080,9 @@ ParallelExtensionTrampoline(dsm_segment *seg, shm_toc *toc)
 static void
 ParallelErrorContext(void *arg)
 {
+#if 0
 	errcontext("parallel worker, pid %d", *(int32 *) arg);
+#endif
 }
 
 /*
diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index 7fb8a1458d..12a59a3560 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -798,6 +798,17 @@ ExplainNode(PlanState *planstate, List *ancestors,
 	int			save_indent = es->indent;
 	bool		haschildren;
 
+	if (IsA(planstate, GatherState))
+	{
+		Gather *gather = (Gather *) plan;
+		if (gather->single_copy)
+		{
+			ExplainNode(outerPlanState(planstate), ancestors, relationship,
+						plan_name, es);
+			return;
+		}
+	}
+
 	switch (nodeTag(plan))
 	{
 		case T_Result:
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index c0db458ad0..34ce39c56a 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -1889,7 +1889,12 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
 			 */
 			bool		need_sort_for_grouping = false;
 
-			result_plan = create_plan(root, best_path);
+			/* Try to run it in a worker. */
+			if (best_path->parallel_safe)
+				best_path = (Path *)
+					create_single_copy_gather_path(root, final_rel,
+												   best_path, NULL);
+
 			current_pathkeys = best_path->pathkeys;
 
 			/* Detect if we'll need an explicit sort for grouping */
@@ -1905,6 +1910,8 @@ grouping_planner(PlannerInfo *root, double tuple_fraction)
 				need_tlist_eval = true;
 			}
 
+			result_plan = create_plan(root, best_path);
+
 			/*
 			 * create_plan returns a plan with just a "flat" tlist of required
 			 * Vars.  Usually we need to insert the sub_tlist as the tlist of
-- 
2.39.5