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Quick hack to allow the outer query's tuple_fraction to be passed down

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to a subquery if the outer query is simple enough that the LIMIT can
be reflected directly to the subquery.  This didn't use to be very
interesting, because a subquery that couldn't have been flattened into
the upper query was usually not going to be very responsive to
tuple_fraction anyway.  But with new code that allows UNION ALL subqueries
to pay attention to tuple_fraction, this is useful to do.  In particular
this lets the optimization occur when the UNION ALL is directly inside
a view.
This commit is contained in:
Tom Lane
2005-06-10 03:32:25 +00:00
parent 453d74b99c
commit a87ee007ed
3 changed files with 49 additions and 4 deletions
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44
src/backend/optimizer/path/allpaths.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.133 2005/06/09 04:18:59 tgl Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.134 2005/06/10 03:32:21 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -353,6 +353,28 @@ set_inherited_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
set_cheapest(rel);
}
/* quick-and-dirty test to see if any joining is needed */
static bool
has_multiple_baserels(PlannerInfo *root)
{
int num_base_rels = 0;
Index rti;
for (rti = 1; rti < root->base_rel_array_size; rti++)
{
RelOptInfo *brel = root->base_rel_array[rti];
if (brel == NULL)
continue;
/* ignore RTEs that are "other rels" */
if (brel->reloptkind == RELOPT_BASEREL)
if (++num_base_rels > 1)
return true;
}
return false;
}
/*
* set_subquery_pathlist
* Build the (single) access path for a subquery RTE
@ -361,8 +383,10 @@ static void
set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel,
Index rti, RangeTblEntry *rte)
{
Query *parse = root->parse;
Query *subquery = rte->subquery;
bool *differentTypes;
double tuple_fraction;
List *pathkeys;
List *subquery_pathkeys;
@ -416,8 +440,24 @@ set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel,
pfree(differentTypes);
/*
* We can safely pass the outer tuple_fraction down to the subquery
* if the outer level has no joining, aggregation, or sorting to do.
* Otherwise we'd better tell the subquery to plan for full retrieval.
* (XXX This could probably be made more intelligent ...)
*/
if (parse->hasAggs ||
parse->groupClause ||
parse->havingQual ||
parse->distinctClause ||
parse->sortClause ||
has_multiple_baserels(root))
tuple_fraction = 0.0; /* default case */
else
tuple_fraction = root->tuple_fraction;
/* Generate the plan for the subquery */
rel->subplan = subquery_planner(subquery, 0.0 /* default case */,
rel->subplan = subquery_planner(subquery, tuple_fraction,
&subquery_pathkeys);
/* Copy number of output rows from subplan */