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Commitfb1879c

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Fix parallel query so it doesn't spoil row estimates above Gather.
Commit45be99f removed GatherPath'snum_workers field, but this is entirely bogus. Normally, a path'sparallel_workers flag is supposed to indicate the number of workersthat it wants, and should be 0 for a non-partial path. In thatcommit, I mistakenly thought that GatherPath could also use that fieldto indicate the number of workers that it would try to start, butthat's disastrous, because then it can propagate up to higher nodes inthe plan tree, which will then get incorrect rowcounts because theparallel_workers flag is involved in computing those values. Repairby putting the separate field back.Report by Tomas Vondra. Patch by me, reviewed by Amit Kapila.Discussion:http://postgr.es/m/f91b4a44-f739-04bd-c4b6-f135bd643669@2ndquadrant.com
1 parent9b6e8d8 commitfb1879c

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4 files changed

+7
-4
lines changed

4 files changed

+7
-4
lines changed

‎src/backend/nodes/outfuncs.c

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Original file line numberDiff line numberDiff line change
@@ -1795,6 +1795,7 @@ _outGatherPath(StringInfo str, const GatherPath *node)
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WRITE_NODE_FIELD(subpath);
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WRITE_BOOL_FIELD(single_copy);
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WRITE_INT_FIELD(num_workers);
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}
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staticvoid

‎src/backend/optimizer/plan/createplan.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1395,7 +1395,7 @@ create_gather_plan(PlannerInfo *root, GatherPath *best_path)
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gather_plan=make_gather(tlist,
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NIL,
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best_path->path.parallel_workers,
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best_path->num_workers,
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best_path->single_copy,
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subplan);
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‎src/backend/optimizer/util/pathnode.c

Lines changed: 4 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -1681,16 +1681,17 @@ create_gather_path(PlannerInfo *root, RelOptInfo *rel, Path *subpath,
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required_outer);
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pathnode->path.parallel_aware= false;
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pathnode->path.parallel_safe= false;
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pathnode->path.parallel_workers=subpath->parallel_workers;
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pathnode->path.parallel_workers=0;
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pathnode->path.pathkeys=NIL;/* Gather has unordered result */
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pathnode->subpath=subpath;
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pathnode->num_workers=subpath->parallel_workers;
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pathnode->single_copy= false;
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if (pathnode->path.parallel_workers==0)
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if (pathnode->num_workers==0)
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{
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pathnode->path.parallel_workers=1;
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pathnode->path.pathkeys=subpath->pathkeys;
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pathnode->num_workers=1;
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pathnode->single_copy= true;
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}
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‎src/include/nodes/relation.h

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Original file line numberDiff line numberDiff line change
@@ -1189,6 +1189,7 @@ typedef struct GatherPath
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Pathpath;
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Path*subpath;/* path for each worker */
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boolsingle_copy;/* path must not be executed >1x */
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intnum_workers;/* number of workers sought to help */
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}GatherPath;
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/*

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