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Fix mistaken failure to allow parallelism in corner case.

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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
This commit is contained in:
Robert Haas
2017-10-27 16:04:01 +02:00
parent 820c0305f6
commit 639c1a6bb9
5 changed files with 7 additions and 2 deletions
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2
src/backend/executor/nodeGather.c
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@ -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;