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Improve UniquePath logic to detect the case where the input is already

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known unique (eg, it is a SELECT DISTINCT ... subquery), and not do a
redundant unique-ification step.
This commit is contained in:
Tom Lane
2004-01-05 18:04:39 +00:00
parent cce442da6d
commit 5c74ce23db
6 changed files with 72 additions and 15 deletions
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34
src/backend/optimizer/util/pathnode.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/util/pathnode.c,v 1.97 2004/01/05 05:07:35 tgl Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/util/pathnode.c,v 1.98 2004/01/05 18:04:39 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -20,12 +20,14 @@
#include "executor/executor.h"
#include "miscadmin.h"
#include "nodes/plannodes.h"
#include "optimizer/clauses.h"
#include "optimizer/cost.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "optimizer/restrictinfo.h"
#include "parser/parse_expr.h"
#include "parser/parse_oper.h"
#include "parser/parsetree.h"
#include "utils/memutils.h"
#include "utils/selfuncs.h"
#include "utils/syscache.h"
@ -546,6 +548,30 @@ create_unique_path(Query *root, RelOptInfo *rel, Path *subpath)
pathnode->subpath = subpath;
/*
* If the input is a subquery that uses DISTINCT, we don't need to do
* anything; its output is already unique. (Are there any other cases
* in which we can easily prove the input must be distinct?)
*/
if (rel->rtekind == RTE_SUBQUERY)
{
RangeTblEntry *rte = rt_fetch(rel->relid, root->rtable);
Query *subquery = rte->subquery;
if (has_distinct_clause(subquery))
{
pathnode->umethod = UNIQUE_PATH_NOOP;
pathnode->rows = rel->rows;
pathnode->path.startup_cost = subpath->startup_cost;
pathnode->path.total_cost = subpath->total_cost;
pathnode->path.pathkeys = subpath->pathkeys;
rel->cheapest_unique_path = (Path *) pathnode;
return pathnode;
}
}
/*
* Try to identify the targetlist that will actually be unique-ified.
* In current usage, this routine is only used for sub-selects of IN
@ -599,7 +625,7 @@ create_unique_path(Query *root, RelOptInfo *rel, Path *subpath)
* compare costs. We only try this if we know the targetlist for sure
* (else we can't be sure about the datatypes involved).
*/
pathnode->use_hash = false;
pathnode->umethod = UNIQUE_PATH_SORT;
if (enable_hashagg && sub_targetlist && hash_safe_tlist(sub_targetlist))
{
/*
@ -617,11 +643,11 @@ create_unique_path(Query *root, RelOptInfo *rel, Path *subpath)
subpath->total_cost,
rel->rows);
if (agg_path.total_cost < sort_path.total_cost)
pathnode->use_hash = true;
pathnode->umethod = UNIQUE_PATH_HASH;
}
}
if (pathnode->use_hash)
if (pathnode->umethod == UNIQUE_PATH_HASH)
{
pathnode->path.startup_cost = agg_path.startup_cost;
pathnode->path.total_cost = agg_path.total_cost;