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Commitb12fd41

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Don't generate parallel paths for rels with parallel-restricted outputs.
Such paths are unsafe. To make it cheaper to detect when this caseapplies, track whether a relation's default PathTarget contains anynon-Vars. In most cases, the answer will be no, which enables us todetermine cheaply that the target list for a proposed path isparallel-safe. However, subquery pull-up can create cases thatrequire us to inspect the target list more carefully.Amit Kapila, reviewed by me.
1 parente7bcd98 commitb12fd41

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5 files changed

+22
-3
lines changed

5 files changed

+22
-3
lines changed

‎src/backend/nodes/outfuncs.c

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2083,6 +2083,7 @@ _outRelOptInfo(StringInfo str, const RelOptInfo *node)
20832083
WRITE_BOOL_FIELD(consider_param_startup);
20842084
WRITE_BOOL_FIELD(consider_parallel);
20852085
WRITE_NODE_FIELD(reltarget);
2086+
WRITE_BOOL_FIELD(reltarget_has_non_vars);
20862087
WRITE_NODE_FIELD(pathlist);
20872088
WRITE_NODE_FIELD(ppilist);
20882089
WRITE_NODE_FIELD(partial_pathlist);

‎src/backend/optimizer/path/allpaths.c

Lines changed: 10 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -608,6 +608,15 @@ set_rel_consider_parallel(PlannerInfo *root, RelOptInfo *rel,
608608
if (has_parallel_hazard((Node*)rel->baserestrictinfo, false))
609609
return;
610610

611+
/*
612+
* If the relation's outputs are not parallel-safe, we must give up.
613+
* In the common case where the relation only outputs Vars, this check is
614+
* very cheap; otherwise, we have to do more work.
615+
*/
616+
if (rel->reltarget_has_non_vars&&
617+
has_parallel_hazard((Node*)rel->reltarget->exprs, false))
618+
return;
619+
611620
/* We have a winner. */
612621
rel->consider_parallel= true;
613622
}
@@ -971,6 +980,7 @@ set_append_rel_size(PlannerInfo *root, RelOptInfo *rel,
971980
adjust_appendrel_attrs(root,
972981
(Node*)rel->reltarget->exprs,
973982
appinfo);
983+
childrel->reltarget_has_non_vars=rel->reltarget_has_non_vars;
974984

975985
/*
976986
* We have to make child entries in the EquivalenceClass data

‎src/backend/optimizer/util/placeholder.c

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -393,6 +393,7 @@ add_placeholders_to_base_rels(PlannerInfo *root)
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394394
rel->reltarget->exprs=lappend(rel->reltarget->exprs,
395395
copyObject(phinfo->ph_var));
396+
rel->reltarget_has_non_vars= true;
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/* reltarget's cost and width fields will be updated later */
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}
398399
}
@@ -427,6 +428,7 @@ add_placeholders_to_joinrel(PlannerInfo *root, RelOptInfo *joinrel,
427428
/* Yup, add it to the output */
428429
joinrel->reltarget->exprs=lappend(joinrel->reltarget->exprs,
429430
phinfo->ph_var);
431+
joinrel->reltarget_has_non_vars= true;
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joinrel->reltarget->width+=phinfo->ph_width;
431433

432434
/*

‎src/backend/optimizer/util/relnode.c

Lines changed: 7 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -109,6 +109,7 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptKind reloptkind)
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rel->consider_parallel= false;/* might get changed later */
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rel->rel_parallel_workers=-1;/* set up in GetRelationInfo */
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rel->reltarget=create_empty_pathtarget();
112+
rel->reltarget_has_non_vars= false;
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rel->pathlist=NIL;
113114
rel->ppilist=NIL;
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rel->partial_pathlist=NIL;
@@ -396,6 +397,7 @@ build_join_rel(PlannerInfo *root,
396397
joinrel->consider_param_startup= false;
397398
joinrel->consider_parallel= false;
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joinrel->reltarget=create_empty_pathtarget();
400+
joinrel->reltarget_has_non_vars= false;
399401
joinrel->pathlist=NIL;
400402
joinrel->ppilist=NIL;
401403
joinrel->partial_pathlist=NIL;
@@ -506,8 +508,8 @@ build_join_rel(PlannerInfo *root,
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* Set the consider_parallel flag if this joinrel could potentially be
507509
* scanned within a parallel worker. If this flag is false for either
508510
* inner_rel or outer_rel, then it must be false for the joinrel also.
509-
* Even if both are true, there might be parallel-restrictedquals at our
510-
*level.
511+
* Even if both are true, there might be parallel-restrictedexpressions
512+
*in the targetlist or quals.
511513
*
512514
* Note that if there are more than two rels in this relation, they could
513515
* be divided between inner_rel and outer_rel in any arbitrary way. We
@@ -517,7 +519,9 @@ build_join_rel(PlannerInfo *root,
517519
* here.
518520
*/
519521
if (inner_rel->consider_parallel&&outer_rel->consider_parallel&&
520-
!has_parallel_hazard((Node*)restrictlist, false))
522+
!has_parallel_hazard((Node*)restrictlist, false)&&
523+
!(joinrel->reltarget_has_non_vars&&
524+
has_parallel_hazard((Node*)joinrel->reltarget->exprs, false)))
521525
joinrel->consider_parallel= true;
522526

523527
/*

‎src/include/nodes/relation.h

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -490,6 +490,8 @@ typedef struct RelOptInfo
490490

491491
/* default result targetlist for Paths scanning this relation */
492492
structPathTarget*reltarget;/* list of Vars/Exprs, cost, width */
493+
boolreltarget_has_non_vars;/* true if any expression in
494+
* PathTarget is a non-Var */
493495

494496
/* materialization information */
495497
List*pathlist;/* Path structures */

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