From 965a16fa9f8c316c30f4ada3c1c98b5dd4666f25 Mon Sep 17 00:00:00 2001
From: Robert Haas <rhaas@postgresql.org>
Date: Fri, 27 Oct 2017 16:04:01 +0200
Subject: [PATCH] Fix mistaken failure to allow parallelism in corner case.
If we try to run a parallel plan in serial mode because, for example,
it's going to be scanned via a cursor, but for some reason we're
already in parallel mode (for example because an outer query is
running in parallel), we'd incorrectly try to launch workers.
Fix by adding a flag to the EState, so that we can be certain that
ExecutePlan() and ExecGather()/ExecGatherMerge() will have the same
idea about whether we are executing serially or in parallel.
Report and fix by Amit Kapila with help from Kuntal Ghosh. A few
tweaks by me.
Discussion: http://postgr.es/m/CAA4eK1+_BuZrmVCeua5Eqnm4Co9DAXdM5HPAOE2J19ePbR912Q@mail.gmail.com
---
src/backend/executor/execMain.c | 1 +
src/backend/executor/execUtils.c | 2 ++
src/backend/executor/nodeGather.c | 2 +-
src/backend/executor/nodeGatherMerge.c | 2 +-
src/include/nodes/execnodes.h | 2 ++
5 files changed, 7 insertions(+), 2 deletions(-)
diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index ac7e0fb48b3..684470928a4 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -1704,6 +1704,7 @@ ExecutePlan(EState *estate,
if (!execute_once || dest->mydest == DestIntoRel)
use_parallel_mode = false;
+ estate->es_use_parallel_mode = use_parallel_mode;
if (use_parallel_mode)
EnterParallelMode();
diff --git a/src/backend/executor/execUtils.c b/src/backend/executor/execUtils.c
index c3988468795..a5925ca7e3b 100644
--- a/src/backend/executor/execUtils.c
+++ b/src/backend/executor/execUtils.c
@@ -156,6 +156,8 @@ CreateExecutorState(void)
estate->es_epqScanDone = NULL;
estate->es_sourceText = NULL;
+ estate->es_use_parallel_mode = false;
+
/*
* Return the executor state structure
*/
diff --git a/src/backend/executor/nodeGather.c b/src/backend/executor/nodeGather.c
index 3be735f5c33..89f592828c1 100644
--- a/src/backend/executor/nodeGather.c
+++ b/src/backend/executor/nodeGather.c
@@ -149,7 +149,7 @@ ExecGather(PlanState *pstate)
* Sometimes we might have to run without parallelism; but if parallel
* mode is active then we can try to fire up some workers.
*/
- if (gather->num_workers > 0 && IsInParallelMode())
+ if (gather->num_workers > 0 && estate->es_use_parallel_mode)
{
ParallelContext *pcxt;
diff --git a/src/backend/executor/nodeGatherMerge.c b/src/backend/executor/nodeGatherMerge.c
index c0c285bd611..6b173543564 100644
--- a/src/backend/executor/nodeGatherMerge.c
+++ b/src/backend/executor/nodeGatherMerge.c
@@ -193,7 +193,7 @@ ExecGatherMerge(PlanState *pstate)
* Sometimes we might have to run without parallelism; but if parallel
* mode is active then we can try to fire up some workers.
*/
- if (gm->num_workers > 0 && IsInParallelMode())
+ if (gm->num_workers > 0 && estate->es_use_parallel_mode)
{
ParallelContext *pcxt;
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 9c790baaaa5..4f5da00c863 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -507,6 +507,8 @@ typedef struct EState
bool *es_epqTupleSet; /* true if EPQ tuple is provided */
bool *es_epqScanDone; /* true if EPQ tuple has been fetched */
+ bool es_use_parallel_mode; /* can we use parallel workers? */
+
/* The per-query shared memory area to use for parallel execution. */
struct dsa_area *es_query_dsa;
} EState;
--
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