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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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4
src/backend/optimizer/util/relnode.c
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@ -513,8 +513,8 @@ build_join_rel(PlannerInfo *root,
* here.
*/
if (inner_rel->consider_parallel && outer_rel->consider_parallel &&
!has_parallel_hazard((Node *) restrictlist, false) &&
!has_parallel_hazard((Node *) joinrel->reltarget->exprs, false))
is_parallel_safe(root, (Node *) restrictlist) &&
is_parallel_safe(root, (Node *) joinrel->reltarget->exprs))
joinrel->consider_parallel = true;
/*