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Don't generate parallel paths for rels with parallel-restricted outputs.

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Such paths are unsafe.  To make it cheaper to detect when this case
applies, track whether a relation's default PathTarget contains any
non-Vars.  In most cases, the answer will be no, which enables us to
determine cheaply that the target list for a proposed path is
parallel-safe.  However, subquery pull-up can create cases that
require us to inspect the target list more carefully.

Amit Kapila, reviewed by me.
This commit is contained in:
Robert Haas
2016-06-09 12:40:23 -04:00
parent e7bcd983f5
commit b12fd41c69
5 changed files with 22 additions and 3 deletions
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10
src/backend/optimizer/util/relnode.c
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@ -109,6 +109,7 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptKind reloptkind)
rel->consider_parallel = false; /* might get changed later */
rel->rel_parallel_workers = -1; /* set up in GetRelationInfo */
rel->reltarget = create_empty_pathtarget();
rel->reltarget_has_non_vars = false;
rel->pathlist = NIL;
rel->ppilist = NIL;
rel->partial_pathlist = NIL;
@ -396,6 +397,7 @@ build_join_rel(PlannerInfo *root,
joinrel->consider_param_startup = false;
joinrel->consider_parallel = false;
joinrel->reltarget = create_empty_pathtarget();
joinrel->reltarget_has_non_vars = false;
joinrel->pathlist = NIL;
joinrel->ppilist = NIL;
joinrel->partial_pathlist = NIL;
@ -506,8 +508,8 @@ build_join_rel(PlannerInfo *root,
* Set the consider_parallel flag if this joinrel could potentially be
* scanned within a parallel worker. If this flag is false for either
* inner_rel or outer_rel, then it must be false for the joinrel also.
* Even if both are true, there might be parallel-restricted quals at our
* level.
* Even if both are true, there might be parallel-restricted expressions
* in the targetlist or quals.
*
* Note that if there are more than two rels in this relation, they could
* be divided between inner_rel and outer_rel in any arbitrary way. We
@ -517,7 +519,9 @@ 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 *) restrictlist, false) &&
!(joinrel->reltarget_has_non_vars &&
has_parallel_hazard((Node *) joinrel->reltarget->exprs, false)))
joinrel->consider_parallel = true;
/*