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Improve planner's estimation of the space needed for HashAgg plans: 

look at the actual aggregate transition datatypes and the actual overhead
needed by nodeAgg.c, instead of using pessimistic round numbers.
Per a discussion with Michael Tiemann.
This commit is contained in:
Tom Lane 2005-01-28 19:34:28 +00:00
parent c3a4e22e82
commit 0bf2587df4
5 changed files with 141 additions and 71 deletions
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22
src/backend/executor/nodeAgg.c
View File

@ -45,7 +45,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/executor/nodeAgg.c,v 1.127 2005/01/27 23:42:18 tgl Exp $
* $PostgreSQL: pgsql/src/backend/executor/nodeAgg.c,v 1.128 2005/01/28 19:33:56 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -604,6 +604,26 @@ build_hash_table(AggState *aggstate)
tmpmem);
}
/*
* Estimate per-hash-table-entry overhead for the planner.
*
* Note that the estimate does not include space for pass-by-reference
* transition data values.
*/
Size
hash_agg_entry_size(int numAggs)
{
Size entrysize;
/* This must match build_hash_table */
entrysize = sizeof(AggHashEntryData) +
(numAggs - 1) *sizeof(AggStatePerGroupData);
/* Account for hashtable overhead */
entrysize += 2 * sizeof(void *);
entrysize = MAXALIGN(entrysize);
return entrysize;
}
/*
* Find or create a hashtable entry for the tuple group containing the
* given tuple.

39
src/backend/optimizer/plan/planner.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.177 2004/12/31 22:00:09 pgsql Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.178 2005/01/28 19:34:05 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -20,6 +20,7 @@
#include "catalog/pg_operator.h"
#include "catalog/pg_type.h"
#include "executor/executor.h"
#include "executor/nodeAgg.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#ifdef OPTIMIZER_DEBUG
@ -660,10 +661,12 @@ grouping_planner(Query *parse, double tuple_fraction)
Path *sorted_path;
double dNumGroups = 0;
long numGroups = 0;
int numAggs = 0;
AggClauseCounts agg_counts;
int numGroupCols = list_length(parse->groupClause);
bool use_hashed_grouping = false;
MemSet(&agg_counts, 0, sizeof(AggClauseCounts));
/* Preprocess targetlist in case we are inside an INSERT/UPDATE. */
tlist = preprocess_targetlist(tlist,
parse->commandType,
@ -752,8 +755,10 @@ grouping_planner(Query *parse, double tuple_fraction)
* the aggregate semantics (eg, producing only one output row).
*/
if (parse->hasAggs)
numAggs = count_agg_clause((Node *) tlist) +
count_agg_clause(parse->havingQual);
{
count_agg_clauses((Node *) tlist, &agg_counts);
count_agg_clauses(parse->havingQual, &agg_counts);
}
/*
* Figure out whether we need a sorted result from query_planner.
@ -990,9 +995,7 @@ grouping_planner(Query *parse, double tuple_fraction)
*/
if (!enable_hashagg || !hash_safe_grouping(parse))
use_hashed_grouping = false;
else if (parse->hasAggs &&
(contain_distinct_agg_clause((Node *) tlist) ||
contain_distinct_agg_clause(parse->havingQual)))
else if (agg_counts.numDistinctAggs != 0)
use_hashed_grouping = false;
else
{
@ -1003,13 +1006,15 @@ grouping_planner(Query *parse, double tuple_fraction)
* the need for sorted input is usually a win, the fact
* that the output won't be sorted may be a loss; so we
* need to do an actual cost comparison.
*
* In most cases we have no good way to estimate the size of
* the transition value needed by an aggregate;
* arbitrarily assume it is 100 bytes. Also set the
* overhead per hashtable entry at 64 bytes.
*/
int hashentrysize = cheapest_path_width + 64 + numAggs * 100;
Size hashentrysize;
/* Estimate per-hash-entry space at tuple width... */
hashentrysize = cheapest_path_width;
/* plus space for pass-by-ref transition values... */
hashentrysize += agg_counts.transitionSpace;
/* plus the per-hash-entry overhead */
hashentrysize += hash_agg_entry_size(agg_counts.numAggs);
if (hashentrysize * dNumGroups <= work_mem * 1024L)
{
@ -1030,7 +1035,7 @@ grouping_planner(Query *parse, double tuple_fraction)
Path sorted_p;
cost_agg(&hashed_p, parse,
AGG_HASHED, numAggs,
AGG_HASHED, agg_counts.numAggs,
numGroupCols, dNumGroups,
cheapest_path->startup_cost,
cheapest_path->total_cost,
@ -1065,7 +1070,7 @@ grouping_planner(Query *parse, double tuple_fraction)
}
if (parse->hasAggs)
cost_agg(&sorted_p, parse,
AGG_SORTED, numAggs,
AGG_SORTED, agg_counts.numAggs,
numGroupCols, dNumGroups,
sorted_p.startup_cost,
sorted_p.total_cost,
@ -1202,7 +1207,7 @@ grouping_planner(Query *parse, double tuple_fraction)
numGroupCols,
groupColIdx,
numGroups,
numAggs,
agg_counts.numAggs,
result_plan);
/* Hashed aggregation produces randomly-ordered results */
current_pathkeys = NIL;
@ -1244,7 +1249,7 @@ grouping_planner(Query *parse, double tuple_fraction)
numGroupCols,
groupColIdx,
numGroups,
numAggs,
agg_counts.numAggs,
result_plan);
}
else

134
src/backend/optimizer/util/clauses.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.186 2004/12/31 22:00:23 pgsql Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.187 2005/01/28 19:34:07 tgl Exp $
*
* HISTORY
* AUTHOR DATE MAJOR EVENT
@ -19,6 +19,7 @@
#include "postgres.h"
#include "catalog/pg_aggregate.h"
#include "catalog/pg_language.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_type.h"
@ -33,6 +34,7 @@
#include "optimizer/var.h"
#include "parser/analyze.h"
#include "parser/parse_clause.h"
#include "parser/parse_coerce.h"
#include "parser/parse_expr.h"
#include "tcop/tcopprot.h"
#include "utils/acl.h"
@ -58,8 +60,7 @@ typedef struct
} substitute_actual_parameters_context;
static bool contain_agg_clause_walker(Node *node, void *context);
static bool contain_distinct_agg_clause_walker(Node *node, void *context);
static bool count_agg_clause_walker(Node *node, int *count);
static bool count_agg_clauses_walker(Node *node, AggClauseCounts *counts);
static bool expression_returns_set_walker(Node *node, void *context);
static bool contain_subplans_walker(Node *node, void *context);
static bool contain_mutable_functions_walker(Node *node, void *context);
@ -358,71 +359,108 @@ contain_agg_clause_walker(Node *node, void *context)
}
/*
* contain_distinct_agg_clause
* Recursively search for DISTINCT Aggref nodes within a clause.
*
* Returns true if any DISTINCT aggregate found.
*
* This does not descend into subqueries, and so should be used only after
* reduction of sublinks to subplans, or in contexts where it's known there
* are no subqueries. There mustn't be outer-aggregate references either.
*/
bool
contain_distinct_agg_clause(Node *clause)
{
return contain_distinct_agg_clause_walker(clause, NULL);
}
static bool
contain_distinct_agg_clause_walker(Node *node, void *context)
{
if (node == NULL)
return false;
if (IsA(node, Aggref))
{
Assert(((Aggref *) node)->agglevelsup == 0);
if (((Aggref *) node)->aggdistinct)
return true; /* abort the tree traversal and return
* true */
}
Assert(!IsA(node, SubLink));
return expression_tree_walker(node, contain_distinct_agg_clause_walker, context);
}
/*
* count_agg_clause
* count_agg_clauses
* Recursively count the Aggref nodes in an expression tree.
*
* Note: this also checks for nested aggregates, which are an error.
*
* We not only count the nodes, but attempt to estimate the total space
* needed for their transition state values if all are evaluated in parallel
* (as would be done in a HashAgg plan). See AggClauseCounts for the exact
* set of statistics returned.
*
* NOTE that the counts are ADDED to those already in *counts ... so the
* caller is responsible for zeroing the struct initially.
*
* This does not descend into subqueries, and so should be used only after
* reduction of sublinks to subplans, or in contexts where it's known there
* are no subqueries. There mustn't be outer-aggregate references either.
*/
int
count_agg_clause(Node *clause)
void
count_agg_clauses(Node *clause, AggClauseCounts *counts)
{
int result = 0;
count_agg_clause_walker(clause, &result);
return result;
/* no setup needed */
count_agg_clauses_walker(clause, counts);
}
static bool
count_agg_clause_walker(Node *node, int *count)
count_agg_clauses_walker(Node *node, AggClauseCounts *counts)
{
if (node == NULL)
return false;
if (IsA(node, Aggref))
{
Assert(((Aggref *) node)->agglevelsup == 0);
(*count)++;
Aggref *aggref = (Aggref *) node;
Oid inputType;
HeapTuple aggTuple;
Form_pg_aggregate aggform;
Oid aggtranstype;
Assert(aggref->agglevelsup == 0);
counts->numAggs++;
if (aggref->aggdistinct)
counts->numDistinctAggs++;
inputType = exprType((Node *) aggref->target);
/* fetch aggregate transition datatype from pg_aggregate */
aggTuple = SearchSysCache(AGGFNOID,
ObjectIdGetDatum(aggref->aggfnoid),
0, 0, 0);
if (!HeapTupleIsValid(aggTuple))
elog(ERROR, "cache lookup failed for aggregate %u",
aggref->aggfnoid);
aggform = (Form_pg_aggregate) GETSTRUCT(aggTuple);
aggtranstype = aggform->aggtranstype;
ReleaseSysCache(aggTuple);
/* resolve actual type of transition state, if polymorphic */
if (aggtranstype == ANYARRAYOID || aggtranstype == ANYELEMENTOID)
{
/* have to fetch the agg's declared input type... */
Oid agg_arg_types[FUNC_MAX_ARGS];
int agg_nargs;
(void) get_func_signature(aggref->aggfnoid,
agg_arg_types, &agg_nargs);
Assert(agg_nargs == 1);
aggtranstype = resolve_generic_type(aggtranstype,
inputType,
agg_arg_types[0]);
}
/*
* If the transition type is pass-by-value then it doesn't add
* anything to the required size of the hashtable. If it is
* pass-by-reference then we have to add the estimated size of
* the value itself, plus palloc overhead.
*/
if (!get_typbyval(aggtranstype))
{
int32 aggtranstypmod;
int32 avgwidth;
/*
* If transition state is of same type as input, assume it's the
* same typmod (same width) as well. This works for cases like
* MAX/MIN and is probably somewhat reasonable otherwise.
*/
if (aggtranstype == inputType)
aggtranstypmod = exprTypmod((Node *) aggref->target);
else
aggtranstypmod = -1;
avgwidth = get_typavgwidth(aggtranstype, aggtranstypmod);
avgwidth = MAXALIGN(avgwidth);
counts->transitionSpace += avgwidth + 2 * sizeof(void *);
}
/*
* Complain if the aggregate's argument contains any aggregates;
* nested agg functions are semantically nonsensical.
*/
if (contain_agg_clause((Node *) ((Aggref *) node)->target))
if (contain_agg_clause((Node *) aggref->target))
ereport(ERROR,
(errcode(ERRCODE_GROUPING_ERROR),
errmsg("aggregate function calls may not be nested")));
@ -433,8 +471,8 @@ count_agg_clause_walker(Node *node, int *count)
return false;
}
Assert(!IsA(node, SubLink));
return expression_tree_walker(node, count_agg_clause_walker,
(void *) count);
return expression_tree_walker(node, count_agg_clauses_walker,
(void *) counts);
}

4
src/include/executor/nodeAgg.h
View File

@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/executor/nodeAgg.h,v 1.23 2004/12/31 22:03:29 pgsql Exp $
* $PostgreSQL: pgsql/src/include/executor/nodeAgg.h,v 1.24 2005/01/28 19:34:18 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -23,6 +23,8 @@ extern TupleTableSlot *ExecAgg(AggState *node);
extern void ExecEndAgg(AggState *node);
extern void ExecReScanAgg(AggState *node, ExprContext *exprCtxt);
extern Size hash_agg_entry_size(int numAggs);
extern Datum aggregate_dummy(PG_FUNCTION_ARGS);
#endif /* NODEAGG_H */

13
src/include/optimizer/clauses.h
View File

@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/optimizer/clauses.h,v 1.77 2004/12/31 22:03:36 pgsql Exp $
* $PostgreSQL: pgsql/src/include/optimizer/clauses.h,v 1.78 2005/01/28 19:34:28 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -17,11 +17,17 @@
#include "nodes/relation.h"
#define is_opclause(clause) ((clause) != NULL && IsA(clause, OpExpr))
#define is_funcclause(clause) ((clause) != NULL && IsA(clause, FuncExpr))
#define is_subplan(clause) ((clause) != NULL && IsA(clause, SubPlan))
typedef struct
{
int numAggs; /* total number of aggregate calls */
int numDistinctAggs; /* number that use DISTINCT */
Size transitionSpace; /* for pass-by-ref transition data */
} AggClauseCounts;
extern Expr *make_opclause(Oid opno, Oid opresulttype, bool opretset,
Expr *leftop, Expr *rightop);
@ -42,8 +48,7 @@ extern Expr *make_ands_explicit(List *andclauses);
extern List *make_ands_implicit(Expr *clause);
extern bool contain_agg_clause(Node *clause);
extern bool contain_distinct_agg_clause(Node *clause);
extern int count_agg_clause(Node *clause);
extern void count_agg_clauses(Node *clause, AggClauseCounts *counts);
extern bool expression_returns_set(Node *clause);