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Add parallel_leader_participation GUC.

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Sometimes, for testing, it's useful to have the leader do nothing but
read tuples from workers; and it's possible that could work out better
even in production.

Thomas Munro, reviewed by Amit Kapila and by me.  A few final tweaks
by me.

Discussion: http://postgr.es/m/CAEepm=2U++Lp3bNTv2Bv_kkr5NE2pOyHhxU=G0YTa4ZhSYhHiw@mail.gmail.com
This commit is contained in:
Robert Haas
2017-11-15 08:17:29 -05:00
parent 7518049980
commit e5253fdc4f
10 changed files with 205 additions and 9 deletions
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8
src/backend/executor/nodeGather.c
View File

@ -38,6 +38,7 @@
#include "executor/nodeSubplan.h"
#include "executor/tqueue.h"
#include "miscadmin.h"
#include "optimizer/planmain.h"
#include "pgstat.h"
#include "utils/memutils.h"
#include "utils/rel.h"
@ -73,7 +74,8 @@ ExecInitGather(Gather *node, EState *estate, int eflags)
gatherstate->ps.ExecProcNode = ExecGather;
gatherstate->initialized = false;
gatherstate->need_to_scan_locally = !node->single_copy;
gatherstate->need_to_scan_locally =
!node->single_copy && parallel_leader_participation;
gatherstate->tuples_needed = -1;
/*
@ -193,9 +195,9 @@ ExecGather(PlanState *pstate)
node->nextreader = 0;
}
/* Run plan locally if no workers or not single-copy. */
/* Run plan locally if no workers or enabled and not single-copy. */
node->need_to_scan_locally = (node->nreaders == 0)
|| !gather->single_copy;
|| (!gather->single_copy && parallel_leader_participation);
node->initialized = true;
}

6
src/backend/executor/nodeGatherMerge.c
View File

@ -23,6 +23,7 @@
#include "executor/tqueue.h"
#include "lib/binaryheap.h"
#include "miscadmin.h"
#include "optimizer/planmain.h"
#include "utils/memutils.h"
#include "utils/rel.h"
@ -233,8 +234,9 @@ ExecGatherMerge(PlanState *pstate)
}
}
/* always allow leader to participate */
node->need_to_scan_locally = true;
/* allow leader to participate if enabled or no choice */
if (parallel_leader_participation || node->nreaders == 0)
node->need_to_scan_locally = true;
node->initialized = true;
}