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

diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index 968942991228bc00883e570b5073f8066bdb37cc..638a856dc392dbeba532a0a3da0e1c8288861eae 100644 (file)
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -1702,6 +1702,7 @@ ExecutePlan(EState *estate,
        if (!execute_once)
                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 ee6c4af055055a6b4579ad18fa6f9b5a0a05f89d..e8c06c76056de57baab9a4790ceb576c5edf8a0c 100644 (file)
--- 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 8370037c4330e441cd81abcd1b7887de2ff80dab..639f4f5af88f24ce6cb586d63cc59dca2ede1660 100644 (file)
--- a/src/backend/executor/nodeGather.c
+++ b/src/backend/executor/nodeGather.c
@@ -150,7 +150,7 @@ 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 70f33a9a28f45af7620f06573ec5c39316c9a2ed..5625b12521004291c75b7814c03cbc5b0925503b 100644 (file)
--- a/src/backend/executor/nodeGatherMerge.c
+++ b/src/backend/executor/nodeGatherMerge.c
@@ -194,7 +194,7 @@ 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 52d35325806625b268405e3f83f5ab2a384653df..8698c8a50c0ba5963becff5c9efea16da3121650 100644 (file)
--- 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;