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Commit716c7d4

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Factor out logic for computing number of parallel workers.
Forthcoming patches to allow other types of parallel scans willneed this logic, or something like it.Dilip Kumar
1 parent0333a73 commit716c7d4

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1 file changed

+60
-43
lines changed

1 file changed

+60
-43
lines changed

‎src/backend/optimizer/path/allpaths.c

Lines changed: 60 additions & 43 deletions
Original file line numberDiff line numberDiff line change
@@ -126,6 +126,7 @@ static void subquery_push_qual(Query *subquery,
126126
staticvoidrecurse_push_qual(Node*setOp,Query*topquery,
127127
RangeTblEntry*rte,Indexrti,Node*qual);
128128
staticvoidremove_unused_subquery_outputs(Query*subquery,RelOptInfo*rel);
129+
staticintcompute_parallel_worker(RelOptInfo*rel,BlockNumberpages);
129130

130131

131132
/*
@@ -678,49 +679,7 @@ create_plain_partial_paths(PlannerInfo *root, RelOptInfo *rel)
678679
{
679680
intparallel_workers;
680681

681-
/*
682-
* If the user has set the parallel_workers reloption, use that; otherwise
683-
* select a default number of workers.
684-
*/
685-
if (rel->rel_parallel_workers!=-1)
686-
parallel_workers=rel->rel_parallel_workers;
687-
else
688-
{
689-
intparallel_threshold;
690-
691-
/*
692-
* If this relation is too small to be worth a parallel scan, just
693-
* return without doing anything ... unless it's an inheritance child.
694-
* In that case, we want to generate a parallel path here anyway. It
695-
* might not be worthwhile just for this relation, but when combined
696-
* with all of its inheritance siblings it may well pay off.
697-
*/
698-
if (rel->pages< (BlockNumber)min_parallel_relation_size&&
699-
rel->reloptkind==RELOPT_BASEREL)
700-
return;
701-
702-
/*
703-
* Select the number of workers based on the log of the size of the
704-
* relation. This probably needs to be a good deal more
705-
* sophisticated, but we need something here for now. Note that the
706-
* upper limit of the min_parallel_relation_size GUC is chosen to
707-
* prevent overflow here.
708-
*/
709-
parallel_workers=1;
710-
parallel_threshold=Max(min_parallel_relation_size,1);
711-
while (rel->pages >= (BlockNumber) (parallel_threshold*3))
712-
{
713-
parallel_workers++;
714-
parallel_threshold *=3;
715-
if (parallel_threshold>INT_MAX /3)
716-
break;/* avoid overflow */
717-
}
718-
}
719-
720-
/*
721-
* In no case use more than max_parallel_workers_per_gather workers.
722-
*/
723-
parallel_workers=Min(parallel_workers,max_parallel_workers_per_gather);
682+
parallel_workers=compute_parallel_worker(rel,rel->pages);
724683

725684
/* If any limit was set to zero, the user doesn't want a parallel scan. */
726685
if (parallel_workers <=0)
@@ -2908,6 +2867,64 @@ remove_unused_subquery_outputs(Query *subquery, RelOptInfo *rel)
29082867
}
29092868
}
29102869

2870+
/*
2871+
* Compute the number of parallel workers that should be used to scan a
2872+
* relation. "pages" is the number of pages from the relation that we
2873+
* expect to scan.
2874+
*/
2875+
staticint
2876+
compute_parallel_worker(RelOptInfo*rel,BlockNumberpages)
2877+
{
2878+
intparallel_workers;
2879+
2880+
/*
2881+
* If the user has set the parallel_workers reloption, use that; otherwise
2882+
* select a default number of workers.
2883+
*/
2884+
if (rel->rel_parallel_workers!=-1)
2885+
parallel_workers=rel->rel_parallel_workers;
2886+
else
2887+
{
2888+
intparallel_threshold;
2889+
2890+
/*
2891+
* If this relation is too small to be worth a parallel scan, just
2892+
* return without doing anything ... unless it's an inheritance child.
2893+
* In that case, we want to generate a parallel path here anyway. It
2894+
* might not be worthwhile just for this relation, but when combined
2895+
* with all of its inheritance siblings it may well pay off.
2896+
*/
2897+
if (pages< (BlockNumber)min_parallel_relation_size&&
2898+
rel->reloptkind==RELOPT_BASEREL)
2899+
return0;
2900+
2901+
/*
2902+
* Select the number of workers based on the log of the size of the
2903+
* relation. This probably needs to be a good deal more
2904+
* sophisticated, but we need something here for now. Note that the
2905+
* upper limit of the min_parallel_relation_size GUC is chosen to
2906+
* prevent overflow here.
2907+
*/
2908+
parallel_workers=1;
2909+
parallel_threshold=Max(min_parallel_relation_size,1);
2910+
while (pages >= (BlockNumber) (parallel_threshold*3))
2911+
{
2912+
parallel_workers++;
2913+
parallel_threshold *=3;
2914+
if (parallel_threshold>INT_MAX /3)
2915+
break;/* avoid overflow */
2916+
}
2917+
}
2918+
2919+
/*
2920+
* In no case use more than max_parallel_workers_per_gather workers.
2921+
*/
2922+
parallel_workers=Min(parallel_workers,max_parallel_workers_per_gather);
2923+
2924+
returnparallel_workers;
2925+
}
2926+
2927+
29112928
/*****************************************************************************
29122929
*DEBUG SUPPORT
29132930
*****************************************************************************/

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