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Commit25442d8

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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_hashjoinwas assuming a target load of one tuple/bucket. This was causing anoticeable underestimate of hashjoin costs.
1 parent24864d0 commit25442d8

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3 files changed

+16
-8
lines changed

3 files changed

+16
-8
lines changed

‎src/backend/executor/nodeHash.c

Lines changed: 1 addition & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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*
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*$Id: nodeHash.c,v 1.44 2000/01/26 05:56:22 momjian Exp $
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*$Id: nodeHash.c,v 1.45 2000/04/18 05:43:01 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -221,7 +221,6 @@ ExecEndHash(Hash *node)
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*create a hashtable in shared memory for hashjoin.
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* ----------------------------------------------------------------
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*/
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#defineNTUP_PER_BUCKET10
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#defineFUDGE_FAC2.0
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HashJoinTable

‎src/backend/optimizer/path/costsize.c

Lines changed: 11 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -42,7 +42,7 @@
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* IDENTIFICATION
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* $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.57 2000/04/12 17:15:19 momjian Exp $
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* $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.58 2000/04/18 05:43:02 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -51,6 +51,7 @@
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#include<math.h>
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#include"executor/nodeHash.h"
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#include"miscadmin.h"
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#include"nodes/plannodes.h"
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#include"optimizer/clauses.h"
@@ -604,12 +605,17 @@ cost_hashjoin(Path *path,
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run_cost+=cpu_operator_cost*outer_path->parent->rows;
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/*
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* the number of tuple comparisons needed is the number of outer
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* tuples times the typical hash bucket size, which we estimate
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* conservatively as the inner disbursion times the inner tuple count.
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* The number of tuple comparisons needed is the number of outer
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* tuples times the typical hash bucket size. nodeHash.c tries for
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* average bucket loading of NTUP_PER_BUCKET, but that goal will
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* be reached only if data values are uniformly distributed among
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* the buckets. To be conservative, we scale up the target bucket
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* size by the number of inner rows times inner disbursion, giving
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* an estimate of the typical number of duplicates of each value.
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* We then charge one cpu_operator_cost per tuple comparison.
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*/
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run_cost+=cpu_operator_cost*outer_path->parent->rows*
612-
ceil(inner_path->parent->rows*innerdisbursion);
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NTUP_PER_BUCKET*ceil(inner_path->parent->rows*innerdisbursion);
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/*
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* Estimate the number of tuples that get through the hashing filter

‎src/include/executor/nodeHash.h

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
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* Portions Copyright (c) 1996-2000, PostgreSQL, Inc
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $Id: nodeHash.h,v 1.15 2000/01/26 05:58:05 momjian Exp $
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* $Id: nodeHash.h,v 1.16 2000/04/18 05:43:00 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -16,6 +16,9 @@
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#include"nodes/plannodes.h"
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/* NTUP_PER_BUCKET is exported because planner wants to see it */
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#defineNTUP_PER_BUCKET10
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externTupleTableSlot*ExecHash(Hash*node);
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externboolExecInitHash(Hash*node,EState*estate,Plan*parent);
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externintExecCountSlotsHash(Hash*node);

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