* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.98 2002/12/30 15:21:21 tgl Exp $
+ * $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.99 2003/01/12 22:35:29 tgl Exp $
*
*-------------------------------------------------------------------------
*/
static Selectivity estimate_hash_bucketsize(Query *root, Var *var,
int nbuckets);
-static bool cost_qual_eval_walker(Node *node, Cost *total);
+static bool cost_qual_eval_walker(Node *node, QualCost *total);
static Selectivity approx_selectivity(Query *root, List *quals);
static void set_rel_width(Query *root, RelOptInfo *rel);
static double relation_byte_size(double tuples, int width);
run_cost += baserel->pages; /* sequential fetches with cost 1.0 */
/* CPU costs */
- cpu_per_tuple = cpu_tuple_cost + baserel->baserestrictcost;
+ startup_cost += baserel->baserestrictcost.startup;
+ cpu_per_tuple = cpu_tuple_cost + baserel->baserestrictcost.per_tuple;
run_cost += cpu_per_tuple * baserel->tuples;
path->startup_cost = startup_cost;
*
* Normally the indexquals will be removed from the list of restriction
* clauses that we have to evaluate as qpquals, so we should subtract
- * their costs from baserestrictcost. XXX For a lossy index, not all
- * the quals will be removed and so we really shouldn't subtract their
- * costs; but detecting that seems more expensive than it's worth.
- * Also, if we are doing a join then some of the indexquals are join
- * clauses and shouldn't be subtracted. Rather than work out exactly
- * how much to subtract, we don't subtract anything.
+ * their costs from baserestrictcost. But if we are doing a join then
+ * some of the indexquals are join clauses and shouldn't be subtracted.
+ * Rather than work out exactly how much to subtract, we don't subtract
+ * anything.
+ *
+ * XXX For a lossy index, not all the quals will be removed and so we
+ * really shouldn't subtract their costs; but detecting that seems more
+ * expensive than it's worth.
*/
- cpu_per_tuple = cpu_tuple_cost + baserel->baserestrictcost;
+ startup_cost += baserel->baserestrictcost.startup;
+ cpu_per_tuple = cpu_tuple_cost + baserel->baserestrictcost.per_tuple;
if (!is_injoin)
- cpu_per_tuple -= cost_qual_eval(indexQuals);
+ {
+ QualCost index_qual_cost;
+
+ cost_qual_eval(&index_qual_cost, indexQuals);
+ cpu_per_tuple -= index_qual_cost.per_tuple;
+ }
run_cost += cpu_per_tuple * tuples_fetched;
run_cost += random_page_cost * ntuples;
/* CPU costs */
- cpu_per_tuple = cpu_tuple_cost + baserel->baserestrictcost;
+ startup_cost += baserel->baserestrictcost.startup;
+ cpu_per_tuple = cpu_tuple_cost + baserel->baserestrictcost.per_tuple;
run_cost += cpu_per_tuple * ntuples;
path->startup_cost = startup_cost;
cpu_per_tuple = cpu_operator_cost;
/* Add scanning CPU costs */
- cpu_per_tuple += cpu_tuple_cost + baserel->baserestrictcost;
+ startup_cost += baserel->baserestrictcost.startup;
+ cpu_per_tuple += cpu_tuple_cost + baserel->baserestrictcost.per_tuple;
run_cost += cpu_per_tuple * baserel->tuples;
path->startup_cost = startup_cost;
Cost startup_cost = 0;
Cost run_cost = 0;
Cost cpu_per_tuple;
+ QualCost restrict_qual_cost;
double ntuples;
if (!enable_nestloop)
ntuples *= outer_path->parent->rows;
/* CPU costs */
- cpu_per_tuple = cpu_tuple_cost + cost_qual_eval(restrictlist);
+ cost_qual_eval(&restrict_qual_cost, restrictlist);
+ startup_cost += restrict_qual_cost.startup;
+ cpu_per_tuple = cpu_tuple_cost + restrict_qual_cost.per_tuple;
run_cost += cpu_per_tuple * ntuples;
path->startup_cost = startup_cost;
Cost startup_cost = 0;
Cost run_cost = 0;
Cost cpu_per_tuple;
+ QualCost restrict_qual_cost;
RestrictInfo *firstclause;
Var *leftvar;
double outer_rows,
outer_path->parent->rows * inner_path->parent->rows;
/* CPU costs */
- cpu_per_tuple = cpu_tuple_cost + cost_qual_eval(restrictlist);
+ cost_qual_eval(&restrict_qual_cost, restrictlist);
+ startup_cost += restrict_qual_cost.startup;
+ cpu_per_tuple = cpu_tuple_cost + restrict_qual_cost.per_tuple;
run_cost += cpu_per_tuple * ntuples;
path->startup_cost = startup_cost;
Cost startup_cost = 0;
Cost run_cost = 0;
Cost cpu_per_tuple;
+ QualCost restrict_qual_cost;
double ntuples;
double outerbytes = relation_byte_size(outer_path->parent->rows,
outer_path->parent->width);
outer_path->parent->rows * inner_path->parent->rows;
/* CPU costs */
- cpu_per_tuple = cpu_tuple_cost + cost_qual_eval(restrictlist);
+ cost_qual_eval(&restrict_qual_cost, restrictlist);
+ startup_cost += restrict_qual_cost.startup;
+ cpu_per_tuple = cpu_tuple_cost + restrict_qual_cost.per_tuple;
run_cost += cpu_per_tuple * ntuples;
/*
/*
* cost_qual_eval
- * Estimate the CPU cost of evaluating a WHERE clause (once).
+ * Estimate the CPU costs of evaluating a WHERE clause.
* The input can be either an implicitly-ANDed list of boolean
* expressions, or a list of RestrictInfo nodes.
+ * The result includes both a one-time (startup) component,
+ * and a per-evaluation component.
*/
-Cost
-cost_qual_eval(List *quals)
+void
+cost_qual_eval(QualCost *cost, List *quals)
{
- Cost total = 0;
List *l;
+ cost->startup = 0;
+ cost->per_tuple = 0;
+
/* We don't charge any cost for the implicit ANDing at top level ... */
foreach(l, quals)
* RestrictInfo nodes contain an eval_cost field reserved for this
* routine's use, so that it's not necessary to evaluate the qual
* clause's cost more than once. If the clause's cost hasn't been
- * computed yet, the field will contain -1.
+ * computed yet, the field's startup value will contain -1.
*/
if (qual && IsA(qual, RestrictInfo))
{
RestrictInfo *restrictinfo = (RestrictInfo *) qual;
- if (restrictinfo->eval_cost < 0)
+ if (restrictinfo->eval_cost.startup < 0)
{
- restrictinfo->eval_cost = 0;
+ restrictinfo->eval_cost.startup = 0;
+ restrictinfo->eval_cost.per_tuple = 0;
cost_qual_eval_walker((Node *) restrictinfo->clause,
&restrictinfo->eval_cost);
}
- total += restrictinfo->eval_cost;
+ cost->startup += restrictinfo->eval_cost.startup;
+ cost->per_tuple += restrictinfo->eval_cost.per_tuple;
}
else
{
/* If it's a bare expression, must always do it the hard way */
- cost_qual_eval_walker(qual, &total);
+ cost_qual_eval_walker(qual, cost);
}
}
- return total;
}
static bool
-cost_qual_eval_walker(Node *node, Cost *total)
+cost_qual_eval_walker(Node *node, QualCost *total)
{
if (node == NULL)
return false;
if (IsA(node, FuncExpr) ||
IsA(node, OpExpr) ||
IsA(node, DistinctExpr))
- *total += cpu_operator_cost;
+ {
+ total->per_tuple += cpu_operator_cost;
+ }
+ else if (IsA(node, SubLink))
+ {
+ /* This routine should not be applied to un-planned expressions */
+ elog(ERROR, "cost_qual_eval: can't handle unplanned sub-select");
+ }
else if (IsA(node, SubPlan))
{
/*
- * A subplan node in an expression indicates that the
- * subplan will be executed on each evaluation, so charge
- * accordingly. (We assume that sub-selects that can be
- * executed as InitPlans have already been removed from
- * the expression.)
+ * A subplan node in an expression typically indicates that the
+ * subplan will be executed on each evaluation, so charge accordingly.
+ * (Sub-selects that can be executed as InitPlans have already been
+ * removed from the expression.)
+ *
+ * An exception occurs when we have decided we can implement the
+ * subplan by hashing.
*
- * NOTE: this logic should agree with the estimates used by
- * make_subplan() in plan/subselect.c.
*/
SubPlan *subplan = (SubPlan *) node;
Plan *plan = subplan->plan;
- Cost subcost;
- if (subplan->subLinkType == EXISTS_SUBLINK)
+ if (subplan->useHashTable)
{
- /* we only need to fetch 1 tuple */
- subcost = plan->startup_cost +
- (plan->total_cost - plan->startup_cost) / plan->plan_rows;
- }
- else if (subplan->subLinkType == ALL_SUBLINK ||
- subplan->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? */
+ /*
+ * If we are using a hash table for the subquery outputs, then
+ * the cost of evaluating the query is a one-time cost.
+ * We charge one cpu_operator_cost per tuple for the work of
+ * loading the hashtable, too.
+ */
+ total->startup += plan->total_cost +
+ cpu_operator_cost * plan->plan_rows;
+ /*
+ * The per-tuple costs include the cost of evaluating the
+ * lefthand expressions, plus the cost of probing the hashtable.
+ * Recursion into the exprs list will handle the lefthand
+ * expressions properly, and will count one cpu_operator_cost
+ * for each comparison operator. That is probably too low for
+ * the probing cost, but it's hard to make a better estimate,
+ * so live with it for now.
+ */
}
else
{
- /* assume we need all tuples */
- subcost = plan->total_cost;
+ /*
+ * Otherwise we will be rescanning the subplan output on each
+ * evaluation. We need to estimate how much of the output
+ * we will actually need to scan. NOTE: this logic should
+ * agree with the estimates used by make_subplan() in
+ * plan/subselect.c.
+ */
+ Cost plan_run_cost = plan->total_cost - plan->startup_cost;
+
+ if (subplan->subLinkType == EXISTS_SUBLINK)
+ {
+ /* we only need to fetch 1 tuple */
+ total->per_tuple += plan_run_cost / plan->plan_rows;
+ }
+ else if (subplan->subLinkType == ALL_SUBLINK ||
+ subplan->subLinkType == ANY_SUBLINK)
+ {
+ /* assume we need 50% of the tuples */
+ total->per_tuple += 0.50 * plan_run_cost;
+ /* also charge a cpu_operator_cost per row examined */
+ total->per_tuple += 0.50 * plan->plan_rows * cpu_operator_cost;
+ }
+ else
+ {
+ /* assume we need all tuples */
+ total->per_tuple += plan_run_cost;
+ }
+ /*
+ * Also account for subplan's startup cost.
+ * If the subplan is uncorrelated or undirect correlated,
+ * AND its topmost node is a Sort or Material node, assume
+ * that we'll only need to pay its startup cost once;
+ * otherwise assume we pay the startup cost every time.
+ */
+ if (subplan->parParam == NIL &&
+ (IsA(plan, Sort) ||
+ IsA(plan, Material)))
+ {
+ total->startup += plan->startup_cost;
+ }
+ else
+ {
+ total->per_tuple += plan->startup_cost;
+ }
}
- *total += subcost;
}
return expression_tree_walker(node, cost_qual_eval_walker,
rel->rows = temp;
- rel->baserestrictcost = cost_qual_eval(rel->baserestrictinfo);
+ cost_qual_eval(&rel->baserestrictcost, rel->baserestrictinfo);
set_rel_width(root, rel);
}
rel->rows = temp;
- rel->baserestrictcost = cost_qual_eval(rel->baserestrictinfo);
+ cost_qual_eval(&rel->baserestrictcost, rel->baserestrictinfo);
set_rel_width(root, rel);
}
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