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Correct oversight in hashjoin cost estimation: nodeHash sizes its hash 

table for an average of NTUP_PER_BUCKET tuples/bucket, but cost_hashjoin
was assuming a target load of one tuple/bucket.  This was causing a
noticeable underestimate of hashjoin costs.
This commit is contained in:
Tom Lane 2000-04-18 05:43:02 +00:00
parent 24864d048e
commit 25442d8d2f
3 changed files with 16 additions and 8 deletions
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3
src/backend/executor/nodeHash.c
View File

@ -7,7 +7,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* $Id: nodeHash.c,v 1.44 2000/01/26 05:56:22 momjian Exp $
* $Id: nodeHash.c,v 1.45 2000/04/18 05:43:01 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -221,7 +221,6 @@ ExecEndHash(Hash *node)
* create a hashtable in shared memory for hashjoin.
* ----------------------------------------------------------------
*/
#define NTUP_PER_BUCKET 10
#define FUDGE_FAC 2.0
HashJoinTable

16
src/backend/optimizer/path/costsize.c
View File

@ -42,7 +42,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.57 2000/04/12 17:15:19 momjian Exp $
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.58 2000/04/18 05:43:02 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -51,6 +51,7 @@
#include <math.h>
#include "executor/nodeHash.h"
#include "miscadmin.h"
#include "nodes/plannodes.h"
#include "optimizer/clauses.h"
@ -604,12 +605,17 @@ cost_hashjoin(Path *path,
run_cost += cpu_operator_cost * outer_path->parent->rows;
/*
* the number of tuple comparisons needed is the number of outer
* tuples times the typical hash bucket size, which we estimate
* conservatively as the inner disbursion times the inner tuple count.
* The number of tuple comparisons needed is the number of outer
* tuples times the typical hash bucket size. nodeHash.c tries for
* average bucket loading of NTUP_PER_BUCKET, but that goal will
* be reached only if data values are uniformly distributed among
* the buckets. To be conservative, we scale up the target bucket
* size by the number of inner rows times inner disbursion, giving
* an estimate of the typical number of duplicates of each value.
* We then charge one cpu_operator_cost per tuple comparison.
*/
run_cost += cpu_operator_cost * outer_path->parent->rows *
ceil(inner_path->parent->rows * innerdisbursion);
NTUP_PER_BUCKET * ceil(inner_path->parent->rows * innerdisbursion);
/*
* Estimate the number of tuples that get through the hashing filter

5
src/include/executor/nodeHash.h
View File

@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2000, PostgreSQL, Inc
* Portions Copyright (c) 1994, Regents of the University of California
*
* $Id: nodeHash.h,v 1.15 2000/01/26 05:58:05 momjian Exp $
* $Id: nodeHash.h,v 1.16 2000/04/18 05:43:00 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -16,6 +16,9 @@
#include "nodes/plannodes.h"
/* NTUP_PER_BUCKET is exported because planner wants to see it */
#define NTUP_PER_BUCKET 10
extern TupleTableSlot *ExecHash(Hash *node);
extern bool ExecInitHash(Hash *node, EState *estate, Plan *parent);
extern int ExecCountSlotsHash(Hash *node);