From e701eee8123682aae4fec5dc9639b50a54eb0b35 Mon Sep 17 00:00:00 2001
From: Kyotaro Horiguchi <horiguchi.kyotaro@lab.ntt.co.jp>
Date: Thu, 16 Feb 2017 19:08:54 +0900
Subject: [PATCH] Don't apply parallel hint on rels that planner considers
 unsafe.

pg_hint_plan considered had its own decision logic on whether
parallel-safe or not but it is dangerous and unnecessary. Just follow
planner's decision.
---
 expected/ut-W.out |  9 ++++++++-
 pg_hint_plan.c    | 24 ++++++++++--------------
 sql/ut-W.sql      |  3 +++
 3 files changed, 21 insertions(+), 15 deletions(-)

diff --git a/expected/ut-W.out b/expected/ut-W.out
index 0828d14..7eecc35 100644
--- a/expected/ut-W.out
+++ b/expected/ut-W.out
@@ -568,13 +568,20 @@ error hint:
                ->  Seq Scan on p2_c3_c2
 (23 rows)
 
+-- This hint doesn't turn on parallel, so the Parallel hint is ignored
+show max_parallel_workers_per_gather;
+ max_parallel_workers_per_gather 
+---------------------------------
+ 0
+(1 row)
+
 /*+Parallel(p1 0 hard) IndexScan(p1) */
 EXPLAIN (COSTS false) SELECT * FROM p1 join p2 on p1.id = p2.id;
 LOG:  pg_hint_plan:
 used hint:
 IndexScan(p1)
-Parallel(p1 0 hard)
 not used hint:
+Parallel(p1 0 hard)
 duplication hint:
 error hint:
 
diff --git a/pg_hint_plan.c b/pg_hint_plan.c
index 6b747c8..477c1f1 100644
--- a/pg_hint_plan.c
+++ b/pg_hint_plan.c
@@ -3089,16 +3089,17 @@ find_parallel_hint(PlannerInfo *root, Index relid)
 	rel = root->simple_rel_array[relid];
 
 	/*
-	 * This function is called for any RelOptInfo or its inheritance parent if
-	 * any. If we are called from inheritance planner, the RelOptInfo for the
-	 * parent of target child relation is not set in the planner info.
-	 *
-	 * Otherwise we should check that the reloptinfo is base relation or
-	 * inheritance children.
+	 * Parallel planning is appliable only on base relation, which has
+	 * RelOptInfo. 
 	 */
-	if (rel &&
-		rel->reloptkind != RELOPT_BASEREL &&
-		rel->reloptkind != RELOPT_OTHER_MEMBER_REL)
+	if (!rel)
+		return NULL;
+
+	/*
+	 * We have set root->glob->parallelModeOK if needed. What we should do here
+	 * is just following the decision of planner.
+	 */
+	if (!rel->consider_parallel)
 		return NULL;
 
 	/*
@@ -3107,11 +3108,6 @@ find_parallel_hint(PlannerInfo *root, Index relid)
 	rte = root->simple_rte_array[relid];
 	Assert(rte);
 
-	/* We don't hint on other than relation and foreign tables */
-	if (rte->rtekind != RTE_RELATION ||
-		rte->relkind == RELKIND_FOREIGN_TABLE)
-		return NULL;
-
 	/* Find parallel method hint, which matches given names, from the list. */
 	for (i = 0; i < current_hint_state->num_hints[HINT_TYPE_PARALLEL]; i++)
 	{
diff --git a/sql/ut-W.sql b/sql/ut-W.sql
index 28cc247..8a35a8a 100644
--- a/sql/ut-W.sql
+++ b/sql/ut-W.sql
@@ -99,6 +99,9 @@ EXPLAIN (COSTS false) SELECT * FROM p1 join p2 on p1.id = p2.id;
 -- we don't have parallel over index scans so far
 /*+Parallel(p1 8 hard) IndexScan(p1) */
 EXPLAIN (COSTS false) SELECT * FROM p1 join p2 on p1.id = p2.id;
+
+-- This hint doesn't turn on parallel, so the Parallel hint is ignored
+show max_parallel_workers_per_gather;
 /*+Parallel(p1 0 hard) IndexScan(p1) */
 EXPLAIN (COSTS false) SELECT * FROM p1 join p2 on p1.id = p2.id;
 
-- 
2.11.0