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Teach the planner to remove SubqueryScan nodes from the plan if they

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aren't doing anything useful (ie, neither selection nor projection).
Also, extend to SubqueryScan the hacks already in place to avoid
unnecessary ExecProject calls when the result would just be the same
tuple the subquery already delivered.  This saves some overhead in
UNION and other set operations, as well as avoiding overhead for
unflatten-able subqueries.  Per example from Sokolov Yura.
This commit is contained in:
Tom Lane
2005-05-22 22:30:20 +00:00
parent c61207b091
commit e2159f3842
13 changed files with 605 additions and 177 deletions
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90
src/backend/optimizer/util/plancat.c
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@@ -9,7 +9,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/util/plancat.c,v 1.106 2005/04/22 21:58:31 tgl Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/util/plancat.c,v 1.107 2005/05/22 22:30:20 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -27,6 +27,7 @@
#include "optimizer/plancat.h"
#include "optimizer/tlist.h"
#include "parser/parsetree.h"
#include "parser/parse_expr.h"
#include "rewrite/rewriteManip.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
@@ -353,50 +354,83 @@ estimate_rel_size(Relation rel, int32 *attr_widths,
* relation, but that data is not readily available to ExecTypeFromTL.
* For now, we don't apply the physical-tlist optimization when there are
* dropped cols.
*
* We also support building a "physical" tlist for subqueries, since the
* same optimization can occur in SubqueryScan nodes.
*/
List *
build_physical_tlist(Query *root, RelOptInfo *rel)
{
List *tlist = NIL;
Index varno = rel->relid;
RangeTblEntry *rte = rt_fetch(varno, root->rtable);
Relation relation;
List *tlist = NIL;
Query *subquery;
Var *var;
ListCell *l;
int attrno,
numattrs;
Assert(rte->rtekind == RTE_RELATION);
relation = heap_open(rte->relid, AccessShareLock);
numattrs = RelationGetNumberOfAttributes(relation);
for (attrno = 1; attrno <= numattrs; attrno++)
switch (rte->rtekind)
{
Form_pg_attribute att_tup = relation->rd_att->attrs[attrno - 1];
Var *var;
case RTE_RELATION:
relation = heap_open(rte->relid, AccessShareLock);
if (att_tup->attisdropped)
{
/* found a dropped col, so punt */
tlist = NIL;
numattrs = RelationGetNumberOfAttributes(relation);
for (attrno = 1; attrno <= numattrs; attrno++)
{
Form_pg_attribute att_tup = relation->rd_att->attrs[attrno - 1];
if (att_tup->attisdropped)
{
/* found a dropped col, so punt */
tlist = NIL;
break;
}
var = makeVar(varno,
attrno,
att_tup->atttypid,
att_tup->atttypmod,
0);
tlist = lappend(tlist,
makeTargetEntry((Expr *) var,
attrno,
NULL,
false));
}
heap_close(relation, AccessShareLock);
break;
}
var = makeVar(varno,
attrno,
att_tup->atttypid,
att_tup->atttypmod,
0);
case RTE_SUBQUERY:
subquery = rte->subquery;
foreach(l, subquery->targetList)
{
TargetEntry *tle = (TargetEntry *) lfirst(l);
tlist = lappend(tlist,
makeTargetEntry((Expr *) var,
attrno,
NULL,
false));
var = makeVar(varno,
tle->resno,
exprType((Node *) tle->expr),
exprTypmod((Node *) tle->expr),
0);
tlist = lappend(tlist,
makeTargetEntry((Expr *) var,
tle->resno,
NULL,
tle->resjunk));
}
break;
default:
/* caller error */
elog(ERROR, "unsupported RTE kind %d in build_physical_tlist",
(int) rte->rtekind);
break;
}
heap_close(relation, AccessShareLock);
return tlist;
}