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Commit0bf2587

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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 overheadneeded by nodeAgg.c, instead of using pessimistic round numbers.Per a discussion with Michael Tiemann.
1 parentc3a4e22 commit0bf2587

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5 files changed

+140
-70
lines changed

5 files changed

+140
-70
lines changed

‎src/backend/executor/nodeAgg.c

Lines changed: 21 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -45,7 +45,7 @@
4545
* Portions Copyright (c) 1994, Regents of the University of California
4646
*
4747
* IDENTIFICATION
48-
* $PostgreSQL: pgsql/src/backend/executor/nodeAgg.c,v 1.127 2005/01/27 23:42:18 tgl Exp $
48+
* $PostgreSQL: pgsql/src/backend/executor/nodeAgg.c,v 1.128 2005/01/28 19:33:56 tgl Exp $
4949
*
5050
*-------------------------------------------------------------------------
5151
*/
@@ -604,6 +604,26 @@ build_hash_table(AggState *aggstate)
604604
tmpmem);
605605
}
606606

607+
/*
608+
* Estimate per-hash-table-entry overhead for the planner.
609+
*
610+
* Note that the estimate does not include space for pass-by-reference
611+
* transition data values.
612+
*/
613+
Size
614+
hash_agg_entry_size(intnumAggs)
615+
{
616+
Sizeentrysize;
617+
618+
/* This must match build_hash_table */
619+
entrysize=sizeof(AggHashEntryData)+
620+
(numAggs-1)*sizeof(AggStatePerGroupData);
621+
/* Account for hashtable overhead */
622+
entrysize+=2*sizeof(void*);
623+
entrysize=MAXALIGN(entrysize);
624+
returnentrysize;
625+
}
626+
607627
/*
608628
* Find or create a hashtable entry for the tuple group containing the
609629
* given tuple.

‎src/backend/optimizer/plan/planner.c

Lines changed: 22 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.177 2004/12/31 22:00:09 pgsql Exp $
11+
* $PostgreSQL: pgsql/src/backend/optimizer/plan/planner.c,v 1.178 2005/01/28 19:34:05 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -20,6 +20,7 @@
2020
#include"catalog/pg_operator.h"
2121
#include"catalog/pg_type.h"
2222
#include"executor/executor.h"
23+
#include"executor/nodeAgg.h"
2324
#include"miscadmin.h"
2425
#include"nodes/makefuncs.h"
2526
#ifdefOPTIMIZER_DEBUG
@@ -660,10 +661,12 @@ grouping_planner(Query *parse, double tuple_fraction)
660661
Path*sorted_path;
661662
doubledNumGroups=0;
662663
longnumGroups=0;
663-
intnumAggs=0;
664+
AggClauseCountsagg_counts;
664665
intnumGroupCols=list_length(parse->groupClause);
665666
booluse_hashed_grouping= false;
666667

668+
MemSet(&agg_counts,0,sizeof(AggClauseCounts));
669+
667670
/* Preprocess targetlist in case we are inside an INSERT/UPDATE. */
668671
tlist=preprocess_targetlist(tlist,
669672
parse->commandType,
@@ -752,8 +755,10 @@ grouping_planner(Query *parse, double tuple_fraction)
752755
* the aggregate semantics (eg, producing only one output row).
753756
*/
754757
if (parse->hasAggs)
755-
numAggs=count_agg_clause((Node*)tlist)+
756-
count_agg_clause(parse->havingQual);
758+
{
759+
count_agg_clauses((Node*)tlist,&agg_counts);
760+
count_agg_clauses(parse->havingQual,&agg_counts);
761+
}
757762

758763
/*
759764
* Figure out whether we need a sorted result from query_planner.
@@ -990,9 +995,7 @@ grouping_planner(Query *parse, double tuple_fraction)
990995
*/
991996
if (!enable_hashagg|| !hash_safe_grouping(parse))
992997
use_hashed_grouping= false;
993-
elseif (parse->hasAggs&&
994-
(contain_distinct_agg_clause((Node*)tlist)||
995-
contain_distinct_agg_clause(parse->havingQual)))
998+
elseif (agg_counts.numDistinctAggs!=0)
996999
use_hashed_grouping= false;
9971000
else
9981001
{
@@ -1003,13 +1006,15 @@ grouping_planner(Query *parse, double tuple_fraction)
10031006
* the need for sorted input is usually a win, the fact
10041007
* that the output won't be sorted may be a loss; so we
10051008
* need to do an actual cost comparison.
1006-
*
1007-
* In most cases we have no good way to estimate the size of
1008-
* the transition value needed by an aggregate;
1009-
* arbitrarily assume it is 100 bytes.Also set the
1010-
* overhead per hashtable entry at 64 bytes.
10111009
*/
1012-
inthashentrysize=cheapest_path_width+64+numAggs*100;
1010+
Sizehashentrysize;
1011+
1012+
/* Estimate per-hash-entry space at tuple width... */
1013+
hashentrysize=cheapest_path_width;
1014+
/* plus space for pass-by-ref transition values... */
1015+
hashentrysize+=agg_counts.transitionSpace;
1016+
/* plus the per-hash-entry overhead */
1017+
hashentrysize+=hash_agg_entry_size(agg_counts.numAggs);
10131018

10141019
if (hashentrysize*dNumGroups <=work_mem*1024L)
10151020
{
@@ -1030,7 +1035,7 @@ grouping_planner(Query *parse, double tuple_fraction)
10301035
Pathsorted_p;
10311036

10321037
cost_agg(&hashed_p,parse,
1033-
AGG_HASHED,numAggs,
1038+
AGG_HASHED,agg_counts.numAggs,
10341039
numGroupCols,dNumGroups,
10351040
cheapest_path->startup_cost,
10361041
cheapest_path->total_cost,
@@ -1065,7 +1070,7 @@ grouping_planner(Query *parse, double tuple_fraction)
10651070
}
10661071
if (parse->hasAggs)
10671072
cost_agg(&sorted_p,parse,
1068-
AGG_SORTED,numAggs,
1073+
AGG_SORTED,agg_counts.numAggs,
10691074
numGroupCols,dNumGroups,
10701075
sorted_p.startup_cost,
10711076
sorted_p.total_cost,
@@ -1202,7 +1207,7 @@ grouping_planner(Query *parse, double tuple_fraction)
12021207
numGroupCols,
12031208
groupColIdx,
12041209
numGroups,
1205-
numAggs,
1210+
agg_counts.numAggs,
12061211
result_plan);
12071212
/* Hashed aggregation produces randomly-ordered results */
12081213
current_pathkeys=NIL;
@@ -1244,7 +1249,7 @@ grouping_planner(Query *parse, double tuple_fraction)
12441249
numGroupCols,
12451250
groupColIdx,
12461251
numGroups,
1247-
numAggs,
1252+
agg_counts.numAggs,
12481253
result_plan);
12491254
}
12501255
else

‎src/backend/optimizer/util/clauses.c

Lines changed: 85 additions & 47 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.186 2004/12/31 22:00:23 pgsql Exp $
11+
* $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.187 2005/01/28 19:34:07 tgl Exp $
1212
*
1313
* HISTORY
1414
* AUTHORDATEMAJOR EVENT
@@ -19,6 +19,7 @@
1919

2020
#include"postgres.h"
2121

22+
#include"catalog/pg_aggregate.h"
2223
#include"catalog/pg_language.h"
2324
#include"catalog/pg_proc.h"
2425
#include"catalog/pg_type.h"
@@ -33,6 +34,7 @@
3334
#include"optimizer/var.h"
3435
#include"parser/analyze.h"
3536
#include"parser/parse_clause.h"
37+
#include"parser/parse_coerce.h"
3638
#include"parser/parse_expr.h"
3739
#include"tcop/tcopprot.h"
3840
#include"utils/acl.h"
@@ -58,8 +60,7 @@ typedef struct
5860
}substitute_actual_parameters_context;
5961

6062
staticboolcontain_agg_clause_walker(Node*node,void*context);
61-
staticboolcontain_distinct_agg_clause_walker(Node*node,void*context);
62-
staticboolcount_agg_clause_walker(Node*node,int*count);
63+
staticboolcount_agg_clauses_walker(Node*node,AggClauseCounts*counts);
6364
staticboolexpression_returns_set_walker(Node*node,void*context);
6465
staticboolcontain_subplans_walker(Node*node,void*context);
6566
staticboolcontain_mutable_functions_walker(Node*node,void*context);
@@ -358,71 +359,108 @@ contain_agg_clause_walker(Node *node, void *context)
358359
}
359360

360361
/*
361-
* contain_distinct_agg_clause
362-
* Recursively search for DISTINCT Aggref nodes within a clause.
362+
* count_agg_clauses
363+
* Recursively count the Aggref nodes in an expression tree.
364+
*
365+
* Note: this also checks for nested aggregates, which are an error.
363366
*
364-
* Returns true if any DISTINCT aggregate found.
367+
* We not only count the nodes, but attempt to estimate the total space
368+
* needed for their transition state values if all are evaluated in parallel
369+
* (as would be done in a HashAgg plan). See AggClauseCounts for the exact
370+
* set of statistics returned.
371+
*
372+
* NOTE that the counts are ADDED to those already in *counts ... so the
373+
* caller is responsible for zeroing the struct initially.
365374
*
366375
* This does not descend into subqueries, and so should be used only after
367376
* reduction of sublinks to subplans, or in contexts where it's known there
368377
* are no subqueries. There mustn't be outer-aggregate references either.
369378
*/
370-
bool
371-
contain_distinct_agg_clause(Node*clause)
379+
void
380+
count_agg_clauses(Node*clause,AggClauseCounts*counts)
372381
{
373-
returncontain_distinct_agg_clause_walker(clause,NULL);
382+
/* no setup needed */
383+
count_agg_clauses_walker(clause,counts);
374384
}
375385

376386
staticbool
377-
contain_distinct_agg_clause_walker(Node*node,void*context)
387+
count_agg_clauses_walker(Node*node,AggClauseCounts*counts)
378388
{
379389
if (node==NULL)
380390
return false;
381391
if (IsA(node,Aggref))
382392
{
383-
Assert(((Aggref*)node)->agglevelsup==0);
384-
if (((Aggref*)node)->aggdistinct)
385-
return true;/* abort the tree traversal and return
386-
* true */
387-
}
388-
Assert(!IsA(node,SubLink));
389-
returnexpression_tree_walker(node,contain_distinct_agg_clause_walker,context);
390-
}
393+
Aggref*aggref= (Aggref*)node;
394+
OidinputType;
395+
HeapTupleaggTuple;
396+
Form_pg_aggregateaggform;
397+
Oidaggtranstype;
398+
399+
Assert(aggref->agglevelsup==0);
400+
counts->numAggs++;
401+
if (aggref->aggdistinct)
402+
counts->numDistinctAggs++;
403+
404+
inputType=exprType((Node*)aggref->target);
405+
406+
/* fetch aggregate transition datatype from pg_aggregate */
407+
aggTuple=SearchSysCache(AGGFNOID,
408+
ObjectIdGetDatum(aggref->aggfnoid),
409+
0,0,0);
410+
if (!HeapTupleIsValid(aggTuple))
411+
elog(ERROR,"cache lookup failed for aggregate %u",
412+
aggref->aggfnoid);
413+
aggform= (Form_pg_aggregate)GETSTRUCT(aggTuple);
414+
aggtranstype=aggform->aggtranstype;
415+
ReleaseSysCache(aggTuple);
416+
417+
/* resolve actual type of transition state, if polymorphic */
418+
if (aggtranstype==ANYARRAYOID||aggtranstype==ANYELEMENTOID)
419+
{
420+
/* have to fetch the agg's declared input type... */
421+
Oidagg_arg_types[FUNC_MAX_ARGS];
422+
intagg_nargs;
423+
424+
(void)get_func_signature(aggref->aggfnoid,
425+
agg_arg_types,&agg_nargs);
426+
Assert(agg_nargs==1);
427+
aggtranstype=resolve_generic_type(aggtranstype,
428+
inputType,
429+
agg_arg_types[0]);
430+
}
391431

392-
/*
393-
* count_agg_clause
394-
* Recursively count the Aggref nodes in an expression tree.
395-
*
396-
* Note: this also checks for nested aggregates, which are an error.
397-
*
398-
* This does not descend into subqueries, and so should be used only after
399-
* reduction of sublinks to subplans, or in contexts where it's known there
400-
* are no subqueries. There mustn't be outer-aggregate references either.
401-
*/
402-
int
403-
count_agg_clause(Node*clause)
404-
{
405-
intresult=0;
432+
/*
433+
* If the transition type is pass-by-value then it doesn't add
434+
* anything to the required size of the hashtable. If it is
435+
* pass-by-reference then we have to add the estimated size of
436+
* the value itself, plus palloc overhead.
437+
*/
438+
if (!get_typbyval(aggtranstype))
439+
{
440+
int32aggtranstypmod;
441+
int32avgwidth;
406442

407-
count_agg_clause_walker(clause,&result);
408-
returnresult;
409-
}
443+
/*
444+
* If transition state is of same type as input, assume it's the
445+
* same typmod (same width) as well. This works for cases like
446+
* MAX/MIN and is probably somewhat reasonable otherwise.
447+
*/
448+
if (aggtranstype==inputType)
449+
aggtranstypmod=exprTypmod((Node*)aggref->target);
450+
else
451+
aggtranstypmod=-1;
410452

411-
staticbool
412-
count_agg_clause_walker(Node*node,int*count)
413-
{
414-
if (node==NULL)
415-
return false;
416-
if (IsA(node,Aggref))
417-
{
418-
Assert(((Aggref*)node)->agglevelsup==0);
419-
(*count)++;
453+
avgwidth=get_typavgwidth(aggtranstype,aggtranstypmod);
454+
avgwidth=MAXALIGN(avgwidth);
455+
456+
counts->transitionSpace+=avgwidth+2*sizeof(void*);
457+
}
420458

421459
/*
422460
* Complain if the aggregate's argument contains any aggregates;
423461
* nested agg functions are semantically nonsensical.
424462
*/
425-
if (contain_agg_clause((Node*)((Aggref*)node)->target))
463+
if (contain_agg_clause((Node*)aggref->target))
426464
ereport(ERROR,
427465
(errcode(ERRCODE_GROUPING_ERROR),
428466
errmsg("aggregate function calls may not be nested")));
@@ -433,8 +471,8 @@ count_agg_clause_walker(Node *node, int *count)
433471
return false;
434472
}
435473
Assert(!IsA(node,SubLink));
436-
returnexpression_tree_walker(node,count_agg_clause_walker,
437-
(void*)count);
474+
returnexpression_tree_walker(node,count_agg_clauses_walker,
475+
(void*)counts);
438476
}
439477

440478

‎src/include/executor/nodeAgg.h

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
88
* Portions Copyright (c) 1994, Regents of the University of California
99
*
10-
* $PostgreSQL: pgsql/src/include/executor/nodeAgg.h,v 1.23 2004/12/31 22:03:29 pgsql Exp $
10+
* $PostgreSQL: pgsql/src/include/executor/nodeAgg.h,v 1.24 2005/01/28 19:34:18 tgl Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -23,6 +23,8 @@ extern TupleTableSlot *ExecAgg(AggState *node);
2323
externvoidExecEndAgg(AggState*node);
2424
externvoidExecReScanAgg(AggState*node,ExprContext*exprCtxt);
2525

26+
externSizehash_agg_entry_size(intnumAggs);
27+
2628
externDatumaggregate_dummy(PG_FUNCTION_ARGS);
2729

2830
#endif/* NODEAGG_H */

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