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Speed up planner's scanning for parallel-query hazards.

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We need to scan the whole parse tree for parallel-unsafe functions.
If there are none, we'll later need to determine whether particular
subtrees contain any parallel-restricted functions.  The previous coding
retained no knowledge from the first scan, even though this is very
wasteful in the common case where the query contains only parallel-safe
functions.  We can bypass all of the later scans by remembering that fact.
This provides a small but measurable speed improvement when the case
applies, and shouldn't cost anything when it doesn't.

Patch by me, reviewed by Robert Haas

Discussion: <3740.1471538387@sss.pgh.pa.us>
This commit is contained in:
Tom Lane
2016-08-19 14:03:07 -04:00
parent 6f79ae7fe5
commit da1c91631e
9 changed files with 138 additions and 85 deletions
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6
src/backend/optimizer/util/pathnode.c
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@ -2178,7 +2178,7 @@ create_projection_path(PlannerInfo *root,
pathnode->path.parallel_aware = false;
pathnode->path.parallel_safe = rel->consider_parallel &&
subpath->parallel_safe &&
!has_parallel_hazard((Node *) target->exprs, false);
is_parallel_safe(root, (Node *) target->exprs);
pathnode->path.parallel_workers = subpath->parallel_workers;
/* Projection does not change the sort order */
pathnode->path.pathkeys = subpath->pathkeys;
@ -2285,7 +2285,7 @@ apply_projection_to_path(PlannerInfo *root,
* target expressions, then we can't.
*/
if (IsA(path, GatherPath) &&
!has_parallel_hazard((Node *) target->exprs, false))
is_parallel_safe(root, (Node *) target->exprs))
{
GatherPath *gpath = (GatherPath *) path;
@ -2306,7 +2306,7 @@ apply_projection_to_path(PlannerInfo *root,
target);
}
else if (path->parallel_safe &&
has_parallel_hazard((Node *) target->exprs, false))
!is_parallel_safe(root, (Node *) target->exprs))
{
/*
* We're inserting a parallel-restricted target list into a path