* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.52 2000/02/15 20:49:16 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.53 2000/03/14 02:23:14 tgl Exp $
*
*-------------------------------------------------------------------------
*/
* (We assume that sub-selects that can be executed as
* InitPlans have already been removed from the expression.)
*
- * NOTE: this logic should agree with make_subplan in
- * subselect.c.
+ * NOTE: this logic should agree with the estimates used by
+ * make_subplan() in plan/subselect.c.
*/
{
SubPlan *subplan = (SubPlan *) expr->oper;
subcost = plan->startup_cost +
(plan->total_cost - plan->startup_cost) / plan->plan_rows;
}
- else if (subplan->sublink->subLinkType == EXPR_SUBLINK)
- {
- /* assume we need all tuples */
- subcost = plan->total_cost;
- }
- else
+ else if (subplan->sublink->subLinkType == ALL_SUBLINK ||
+ subplan->sublink->subLinkType == ANY_SUBLINK)
{
/* assume we need 50% of the tuples */
subcost = plan->startup_cost +
0.50 * (plan->total_cost - plan->startup_cost);
+ /* XXX what if subplan has been materialized? */
+ }
+ else
+ {
+ /* assume we need all tuples */
+ subcost = plan->total_cost;
}
*total += subcost;
}
*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planner.c,v 1.76 2000/02/21 01:13:04 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planner.c,v 1.77 2000/03/14 02:23:15 tgl Exp $
*
*-------------------------------------------------------------------------
*/
* In GROUP BY mode, we have the little problem that we don't
* really know how many input tuples will be needed to make a
* group, so we can't translate an output LIMIT count into an
- * input count. For lack of a better idea, assume 10% of the
+ * input count. For lack of a better idea, assume 25% of the
* input data will be processed if there is any output limit.
+ * However, if the caller gave us a fraction rather than an
+ * absolute count, we can keep using that fraction (which amounts
+ * to assuming that all the groups are about the same size).
*/
- if (tuple_fraction > 0.0)
- tuple_fraction = 0.10;
+ if (tuple_fraction >= 1.0)
+ tuple_fraction = 0.25;
/*
* If both GROUP BY and ORDER BY are specified, we will need
* two levels of sort --- and, therefore, certainly need to
{
/*
* SELECT DISTINCT, like GROUP, will absorb an unpredictable
- * number of input tuples per output tuple. So, fall back to
- * our same old 10% default...
+ * number of input tuples per output tuple. Handle the same way.
*/
- if (tuple_fraction > 0.0)
- tuple_fraction = 0.10;
+ if (tuple_fraction >= 1.0)
+ tuple_fraction = 0.25;
}
/* Generate the (sub) plan */
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/optimizer/plan/subselect.c,v 1.30 2000/03/11 23:53:41 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/optimizer/plan/subselect.c,v 1.31 2000/03/14 02:23:15 tgl Exp $
*
*-------------------------------------------------------------------------
*/
PlannerInitPlan = NULL;
- PlannerQueryLevel++; /* we becomes child */
+ PlannerQueryLevel++; /* we become child */
/*
* For an EXISTS subplan, tell lower-level planner to expect that
- * only the first tuple will be retrieved. For ALL, ANY, and MULTIEXPR
- * subplans, we will be able to stop evaluating if the test condition
- * fails, so very often not all the tuples will be retrieved; for lack
- * of a better idea, specify 50% retrieval. For EXPR_SUBLINK use default
- * behavior.
+ * only the first tuple will be retrieved. For ALL and ANY subplans,
+ * we will be able to stop evaluating if the test condition fails,
+ * so very often not all the tuples will be retrieved; for lack of a
+ * better idea, specify 50% retrieval. For EXPR and MULTIEXPR subplans,
+ * use default behavior (we're only expecting one row out, anyway).
*
- * NOTE: if you change these numbers, also change cost_qual_eval_walker
- * in costsize.c.
+ * NOTE: if you change these numbers, also change cost_qual_eval_walker()
+ * in path/costsize.c.
+ *
+ * XXX If an ALL/ANY subplan is uncorrelated, we may decide to materialize
+ * its result below. In that case it would've been better to specify
+ * full retrieval. At present, however, we can only detect correlation
+ * or lack of it after we've made the subplan :-(. Perhaps detection
+ * of correlation should be done as a separate step. Meanwhile, we don't
+ * want to be too optimistic about the percentage of tuples retrieved,
+ * for fear of selecting a plan that's bad for the materialization case.
*/
if (slink->subLinkType == EXISTS_SUBLINK)
tuple_fraction = 1.0; /* just like a LIMIT 1 */
- else if (slink->subLinkType == EXPR_SUBLINK)
- tuple_fraction = -1.0; /* default behavior */
- else
+ else if (slink->subLinkType == ALL_SUBLINK ||
+ slink->subLinkType == ANY_SUBLINK)
tuple_fraction = 0.5; /* 50% */
+ else
+ tuple_fraction = -1.0; /* default behavior */
node->plan = plan = union_planner(subquery, tuple_fraction);
OSDN Git Service
