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Fix costing for parallel aggregation.

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The original patch kind of ignored the fact that we were doing something
different from a costing point of view, but nobody noticed.  This patch
fixes that oversight.

David Rowley
This commit is contained in:
Robert Haas
2016-04-12 16:24:55 -04:00
parent 46d73e0d65
commit deb71fa971
3 changed files with 92 additions and 25 deletions
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39
src/backend/optimizer/plan/planner.c
View File

@@ -3262,6 +3262,8 @@ create_grouping_paths(PlannerInfo *root,
RelOptInfo *grouped_rel;
PathTarget *partial_grouping_target = NULL;
AggClauseCosts agg_costs;
AggClauseCosts agg_partial_costs; /* parallel only */
AggClauseCosts agg_final_costs; /* parallel only */
Size hashaggtablesize;
double dNumGroups;
double dNumPartialGroups = 0;
@@ -3346,8 +3348,10 @@ create_grouping_paths(PlannerInfo *root,
MemSet(&agg_costs, 0, sizeof(AggClauseCosts));
if (parse->hasAggs)
{
count_agg_clauses(root, (Node *) target->exprs, &agg_costs);
count_agg_clauses(root, parse->havingQual, &agg_costs);
count_agg_clauses(root, (Node *) target->exprs, &agg_costs, true,
false, false);
count_agg_clauses(root, parse->havingQual, &agg_costs, true, false,
false);
}
/*
@@ -3422,6 +3426,25 @@ create_grouping_paths(PlannerInfo *root,
NIL,
NIL);
/*
* Collect statistics about aggregates for estimating costs of
* performing aggregation in parallel.
*/
MemSet(&agg_partial_costs, 0, sizeof(AggClauseCosts));
MemSet(&agg_final_costs, 0, sizeof(AggClauseCosts));
if (parse->hasAggs)
{
/* partial phase */
count_agg_clauses(root, (Node *) partial_grouping_target->exprs,
&agg_partial_costs, false, false, true);
/* final phase */
count_agg_clauses(root, (Node *) target->exprs, &agg_final_costs,
true, true, true);
count_agg_clauses(root, parse->havingQual, &agg_final_costs, true,
true, true);
}
if (can_sort)
{
/* Checked in set_grouped_rel_consider_parallel() */
@@ -3457,7 +3480,7 @@ create_grouping_paths(PlannerInfo *root,
parse->groupClause ? AGG_SORTED : AGG_PLAIN,
parse->groupClause,
NIL,
&agg_costs,
&agg_partial_costs,
dNumPartialGroups,
false,
false,
@@ -3482,7 +3505,7 @@ create_grouping_paths(PlannerInfo *root,
hashaggtablesize =
estimate_hashagg_tablesize(cheapest_partial_path,
&agg_costs,
&agg_partial_costs,
dNumPartialGroups);
/*
@@ -3499,7 +3522,7 @@ create_grouping_paths(PlannerInfo *root,
AGG_HASHED,
parse->groupClause,
NIL,
&agg_costs,
&agg_partial_costs,
dNumPartialGroups,
false,
false,
@@ -3631,7 +3654,7 @@ create_grouping_paths(PlannerInfo *root,
parse->groupClause ? AGG_SORTED : AGG_PLAIN,
parse->groupClause,
(List *) parse->havingQual,
&agg_costs,
&agg_final_costs,
dNumGroups,
true,
true,
@@ -3691,7 +3714,7 @@ create_grouping_paths(PlannerInfo *root,
Path *path = (Path *) linitial(grouped_rel->partial_pathlist);
hashaggtablesize = estimate_hashagg_tablesize(path,
&agg_costs,
&agg_final_costs,
dNumGroups);
if (hashaggtablesize < work_mem * 1024L)
@@ -3713,7 +3736,7 @@ create_grouping_paths(PlannerInfo *root,
AGG_HASHED,
parse->groupClause,
(List *) parse->havingQual,
&agg_costs,
&agg_final_costs,
dNumGroups,
true,
true,

53
src/backend/optimizer/util/clauses.c
View File

@@ -61,6 +61,9 @@ typedef struct
{
PlannerInfo *root;
AggClauseCosts *costs;
bool finalizeAggs;
bool combineStates;
bool serialStates;
} count_agg_clauses_context;
typedef struct
@@ -540,12 +543,16 @@ contain_agg_clause_walker(Node *node, void *context)
* are no subqueries. There mustn't be outer-aggregate references either.
*/
void
count_agg_clauses(PlannerInfo *root, Node *clause, AggClauseCosts *costs)
count_agg_clauses(PlannerInfo *root, Node *clause, AggClauseCosts *costs,
bool finalizeAggs, bool combineStates, bool serialStates)
{
count_agg_clauses_context context;
context.root = root;
context.costs = costs;
context.finalizeAggs = finalizeAggs;
context.combineStates = combineStates;
context.serialStates = serialStates;
(void) count_agg_clauses_walker(clause, &context);
}
@@ -562,6 +569,9 @@ count_agg_clauses_walker(Node *node, count_agg_clauses_context *context)
Form_pg_aggregate aggform;
Oid aggtransfn;
Oid aggfinalfn;
Oid aggcombinefn;
Oid aggserialfn;
Oid aggdeserialfn;
Oid aggtranstype;
int32 aggtransspace;
QualCost argcosts;
@@ -583,6 +593,9 @@ count_agg_clauses_walker(Node *node, count_agg_clauses_context *context)
aggform = (Form_pg_aggregate) GETSTRUCT(aggTuple);
aggtransfn = aggform->aggtransfn;
aggfinalfn = aggform->aggfinalfn;
aggcombinefn = aggform->aggcombinefn;
aggserialfn = aggform->aggserialfn;
aggdeserialfn = aggform->aggdeserialfn;
aggtranstype = aggform->aggtranstype;
aggtransspace = aggform->aggtransspace;
ReleaseSysCache(aggTuple);
@@ -592,12 +605,40 @@ count_agg_clauses_walker(Node *node, count_agg_clauses_context *context)
if (aggref->aggorder != NIL || aggref->aggdistinct != NIL)
costs->numOrderedAggs++;
/* add component function execution costs to appropriate totals */
/*
* Add the appropriate component function execution costs to
* appropriate totals.
*/
if (context->combineStates)
{
/* charge for combining previously aggregated states */
costs->transCost.per_tuple += get_func_cost(aggcombinefn) * cpu_operator_cost;
/* charge for deserialization, when appropriate */
if (context->serialStates && OidIsValid(aggdeserialfn))
costs->transCost.per_tuple += get_func_cost(aggdeserialfn) * cpu_operator_cost;
}
else
costs->transCost.per_tuple += get_func_cost(aggtransfn) * cpu_operator_cost;
if (context->finalizeAggs)
{
if (OidIsValid(aggfinalfn))
costs->finalCost += get_func_cost(aggfinalfn) * cpu_operator_cost;
}
else if (context->serialStates)
{
if (OidIsValid(aggserialfn))
costs->finalCost += get_func_cost(aggserialfn) * cpu_operator_cost;
}
/* also add the input expressions' cost to per-input-row costs */
/*
* Some costs will already have been incurred by the initial aggregate
* node, so we mustn't include these again.
*/
if (!context->combineStates)
{
/* add the input expressions' cost to per-input-row costs */
cost_qual_eval_node(&argcosts, (Node *) aggref->args, context->root);
costs->transCost.startup += argcosts.startup;
costs->transCost.per_tuple += argcosts.per_tuple;
@@ -605,8 +646,9 @@ count_agg_clauses_walker(Node *node, count_agg_clauses_context *context)
/*
* Add any filter's cost to per-input-row costs.
*
* XXX Ideally we should reduce input expression costs according to
* filter selectivity, but it's not clear it's worth the trouble.
* XXX Ideally we should reduce input expression costs according
* to filter selectivity, but it's not clear it's worth the
* trouble.
*/
if (aggref->aggfilter)
{
@@ -615,6 +657,7 @@ count_agg_clauses_walker(Node *node, count_agg_clauses_context *context)
costs->transCost.startup += argcosts.startup;
costs->transCost.per_tuple += argcosts.per_tuple;
}
}
/*
* If there are direct arguments, treat their evaluation cost like the

3
src/include/optimizer/clauses.h
View File

@@ -67,7 +67,8 @@ extern List *make_ands_implicit(Expr *clause);
extern PartialAggType aggregates_allow_partial(Node *clause);
extern bool contain_agg_clause(Node *clause);
extern void count_agg_clauses(PlannerInfo *root, Node *clause,
AggClauseCosts *costs);
AggClauseCosts *costs, bool finalizeAggs,
bool combineStates, bool serialStates);
extern bool contain_window_function(Node *clause);
extern WindowFuncLists *find_window_functions(Node *clause, Index maxWinRef);