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Apply a MATERIAL node to the result of an uncorrelated subplan, if it 

looks like it will save computation to do so.
This commit is contained in:
Tom Lane 2000-03-02 04:08:16 +00:00
parent 9f198423df
commit 0eb5ab8250
1 changed files with 71 additions and 5 deletions
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76
src/backend/optimizer/plan/subselect.c
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@ -7,7 +7,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/optimizer/plan/subselect.c,v 1.28 2000/02/15 20:49:18 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/optimizer/plan/subselect.c,v 1.29 2000/03/02 04:08:16 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -18,6 +18,8 @@
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/clauses.h"
#include "optimizer/cost.h"
#include "optimizer/planmain.h"
#include "optimizer/planner.h"
#include "optimizer/subselect.h"
#include "parser/parse_expr.h"
@ -123,6 +125,7 @@ static Node *
make_subplan(SubLink *slink)
{
SubPlan *node = makeNode(SubPlan);
Query *subquery = (Query *) (slink->subselect);
double tuple_fraction;
Plan *plan;
List *lst;
@ -151,8 +154,7 @@ make_subplan(SubLink *slink)
else
tuple_fraction = 0.5; /* 50% */
node->plan = plan = union_planner((Query *) slink->subselect,
tuple_fraction);
node->plan = plan = union_planner(subquery, tuple_fraction);
/*
* Assign subPlan, extParam and locParam to plan nodes. At the moment,
@ -179,7 +181,7 @@ make_subplan(SubLink *slink)
PlannerQueryLevel--;
node->plan_id = PlannerPlanId++;
node->rtable = ((Query *) slink->subselect)->rtable;
node->rtable = subquery->rtable;
node->sublink = slink;
slink->subselect = NULL; /* cool ?! */
@ -287,12 +289,76 @@ make_subplan(SubLink *slink)
}
else
{
/* make expression of SUBPLAN type */
Expr *expr = makeNode(Expr);
List *args = NIL;
List *newoper = NIL;
int i = 0;
/*
* We can't convert subplans of ALL_SUBLINK or ANY_SUBLINK types to
* initPlans, even when they are uncorrelated or undirect correlated,
* because we need to scan the output of the subplan for each outer
* tuple. However, we have the option to tack a MATERIAL node onto
* the top of an uncorrelated/undirect correlated subplan, which lets
* us do the work of evaluating the subplan only once. We do this
* if the subplan's top plan node is anything more complicated than
* a sequential or index scan, and we do it even for those plan types
* if the qual appears selective enough to eliminate many tuples.
*/
if (node->parParam == NIL)
{
bool use_material;
switch (nodeTag(plan))
{
case T_SeqScan:
{
Selectivity qualsel;
qualsel = clauselist_selectivity(subquery, plan->qual, 0);
/* Is 10% selectivity a good threshold?? */
use_material = qualsel < 0.10;
break;
}
case T_IndexScan:
{
List *indxqual = ((IndexScan *) plan)->indxqualorig;
Selectivity qualsel;
qualsel = clauselist_selectivity(subquery, plan->qual, 0);
qualsel *= clauselist_selectivity(subquery, indxqual, 0);
/* Note: if index is lossy, we just double-counted the
* index selectivity. Worth fixing?
*/
/* Is 10% selectivity a good threshold?? */
use_material = qualsel < 0.10;
break;
}
case T_Material:
case T_Sort:
/* Don't add another Material node if there's one already,
* nor if the top node is a Sort, since Sort materializes
* its output anyway. (I doubt either case can happen in
* practice for a subplan, but...)
*/
use_material = false;
break;
default:
use_material = true;
break;
}
if (use_material)
{
plan = (Plan *) make_noname(plan->targetlist,
NIL,
plan);
node->plan = plan;
}
}
/*
* Make expression of SUBPLAN type
*/
expr->typeOid = BOOLOID; /* bogus, but we don't really care */
expr->opType = SUBPLAN_EXPR;
expr->oper = (Node *) node;