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Second thoughts dept: arrange to cache mergejoin scan selectivity
in RestrictInfo nodes, instead of recomputing on every use.
1 parent f8c1095 commit 8f0a9e8

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6 files changed

+34
-13
lines changed

6 files changed

+34
-13
lines changed

‎src/backend/nodes/copyfuncs.c

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -15,7 +15,7 @@
1515
* Portions Copyright (c) 1994, Regents of the University of California
1616
*
1717
* IDENTIFICATION
18-
* $Header: /cvsroot/pgsql/src/backend/nodes/copyfuncs.c,v 1.163 2002/02/26 22:47:05 tgl Exp $
18+
* $Header: /cvsroot/pgsql/src/backend/nodes/copyfuncs.c,v 1.164 2002/03/01 06:01:18 tgl Exp $
1919
*
2020
*-------------------------------------------------------------------------
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*/
@@ -1406,6 +1406,8 @@ _copyRestrictInfo(RestrictInfo *from)
14061406
*/
14071407
newnode->left_pathkey = NIL;
14081408
newnode->right_pathkey = NIL;
1409+
newnode->left_mergescansel = from->left_mergescansel;
1410+
newnode->right_mergescansel = from->right_mergescansel;
14091411
newnode->hashjoinoperator = from->hashjoinoperator;
14101412
newnode->left_bucketsize = from->left_bucketsize;
14111413
newnode->right_bucketsize = from->right_bucketsize;

‎src/backend/nodes/readfuncs.c

Lines changed: 4 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $Header: /cvsroot/pgsql/src/backend/nodes/readfuncs.c,v 1.114 2002/02/26 22:47:07 tgl Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/nodes/readfuncs.c,v 1.115 2002/03/01 06:01:18 tgl Exp $
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*
1313
* NOTES
1414
* Most of the read functions for plan nodes are tested. (In fact, they
@@ -1846,9 +1846,11 @@ _readRestrictInfo(void)
18461846
local_node->eval_cost = -1;
18471847
/* ditto for this_selec */
18481848
local_node->this_selec = -1;
1849-
/* ditto for cached pathkeys and bucketsize */
1849+
/* ditto for cached pathkeys, selectivity, bucketsize */
18501850
local_node->left_pathkey = NIL;
18511851
local_node->right_pathkey = NIL;
1852+
local_node->left_mergescansel = -1;
1853+
local_node->right_mergescansel = -1;
18521854
local_node->left_bucketsize = -1;
18531855
local_node->right_bucketsize = -1;
18541856

‎src/backend/optimizer/path/costsize.c

Lines changed: 16 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -42,7 +42,7 @@
4242
* Portions Copyright (c) 1994, Regents of the University of California
4343
*
4444
* IDENTIFICATION
45-
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.80 2002/03/01 04:09:24 tgl Exp $
45+
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.81 2002/03/01 06:01:19 tgl Exp $
4646
*
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*-------------------------------------------------------------------------
4848
*/
@@ -566,6 +566,7 @@ cost_mergejoin(Path *path, Query *root,
566566
Cost startup_cost = 0;
567567
Cost run_cost = 0;
568568
Cost cpu_per_tuple;
569+
RestrictInfo *firstclause;
569570
double outer_rows,
570571
inner_rows;
571572
double ntuples;
@@ -581,10 +582,18 @@ cost_mergejoin(Path *path, Query *root,
581582
* Estimate fraction of the left and right inputs that will actually
582583
* need to be scanned. We use only the first (most significant)
583584
* merge clause for this purpose.
585+
*
586+
* Since this calculation is somewhat expensive, and will be the same
587+
* for all mergejoin paths associated with the merge clause, we cache
588+
* the results in the RestrictInfo node.
584589
*/
585-
mergejoinscansel(root,
586-
(Node *) ((RestrictInfo *) lfirst(mergeclauses))->clause,
587-
&leftscan, &rightscan);
590+
firstclause = (RestrictInfo *) lfirst(mergeclauses);
591+
if (firstclause->left_mergescansel < 0) /* not computed yet? */
592+
mergejoinscansel(root, (Node *) firstclause->clause,
593+
&firstclause->left_mergescansel,
594+
&firstclause->right_mergescansel);
595+
leftscan = firstclause->left_mergescansel;
596+
rightscan = firstclause->right_mergescansel;
588597

589598
outer_rows = outer_path->parent->rows * leftscan;
590599
inner_rows = inner_path->parent->rows * rightscan;
@@ -1099,9 +1108,9 @@ cost_qual_eval_walker(Node *node, Cost *total)
10991108
* big difference.)
11001109
*
11011110
* The "dirty" part comes from the fact that the selectivities of multiple
1102-
* clauses are estimated independently and multiplied together. Currently,
1103-
* clauselist_selectivity can seldom do any better than that anyhow, but
1104-
* someday it might be smarter.
1111+
* clauses are estimated independently and multiplied together. Now
1112+
* clauselist_selectivity often can't do any better than that anyhow, but
1113+
* for some situations (such as range constraints) it is smarter.
11051114
*
11061115
* Since we are only using the results to estimate how many potential
11071116
* output tuples are generated and passed through qpqual checking, it

‎src/backend/optimizer/plan/initsplan.c

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $Header: /cvsroot/pgsql/src/backend/optimizer/plan/initsplan.c,v 1.65 2001/10/25 05:49:33 momjian Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/optimizer/plan/initsplan.c,v 1.66 2002/03/01 06:01:19 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -370,6 +370,8 @@ distribute_qual_to_rels(Query *root, Node *clause,
370370
restrictinfo->right_sortop = InvalidOid;
371371
restrictinfo->left_pathkey = NIL; /* not computable yet */
372372
restrictinfo->right_pathkey = NIL;
373+
restrictinfo->left_mergescansel = -1; /* not computed until needed */
374+
restrictinfo->right_mergescansel = -1;
373375
restrictinfo->hashjoinoperator = InvalidOid;
374376
restrictinfo->left_bucketsize = -1; /* not computed until needed */
375377
restrictinfo->right_bucketsize = -1;

‎src/backend/optimizer/prep/prepunion.c

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -14,7 +14,7 @@
1414
*
1515
*
1616
* IDENTIFICATION
17-
* $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepunion.c,v 1.69 2001/11/12 20:04:20 tgl Exp $
17+
* $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepunion.c,v 1.70 2002/03/01 06:01:20 tgl Exp $
1818
*
1919
*-------------------------------------------------------------------------
2020
*/
@@ -777,6 +777,8 @@ adjust_inherited_attrs_mutator(Node *node,
777777
newinfo->this_selec = -1;
778778
newinfo->left_pathkey = NIL; /* and these */
779779
newinfo->right_pathkey = NIL;
780+
newinfo->left_mergescansel = -1;
781+
newinfo->right_mergescansel = -1;
780782
newinfo->left_bucketsize = -1;
781783
newinfo->right_bucketsize = -1;
782784

‎src/include/nodes/relation.h

Lines changed: 5 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
88
* Portions Copyright (c) 1994, Regents of the University of California
99
*
10-
* $Id: relation.h,v 1.61 2001/11/05 17:46:34 momjian Exp $
10+
* $Id: relation.h,v 1.62 2002/03/01 06:01:20 tgl Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -521,6 +521,10 @@ typedef struct RestrictInfo
521521
List *left_pathkey; /* canonical pathkey for left side */
522522
List *right_pathkey; /* canonical pathkey for right side */
523523

524+
/* cache space for mergeclause processing; -1 if not yet set */
525+
Selectivity left_mergescansel; /* fraction of left side to scan */
526+
Selectivity right_mergescansel; /* fraction of right side to scan */
527+
524528
/* valid if clause is hashjoinable, else InvalidOid: */
525529
Oid hashjoinoperator; /* copy of clause operator */
526530

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