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Commit6161766

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Adjust remove_redundant_join_clauses() so that when it has a choice
of which redundant clause to remove, it removes the more expensive one.In simple scenarios the clauses will be like 'var = var' and there'sno difference, but we are now capable of considering cases where thereare sub-selects in the clauses, and it makes a BIG difference.
1 parentdf79b84 commit6161766

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+60
-29
lines changed

1 file changed

+60
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lines changed

‎src/backend/optimizer/util/restrictinfo.c‎

Lines changed: 60 additions & 29 deletions
Original file line numberDiff line numberDiff line change
@@ -8,13 +8,14 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/optimizer/util/restrictinfo.c,v 1.25 2004/01/05 23:39:54 tgl Exp $
11+
* $PostgreSQL: pgsql/src/backend/optimizer/util/restrictinfo.c,v 1.26 2004/02/27 21:48:04 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
1515
#include"postgres.h"
1616

1717
#include"optimizer/clauses.h"
18+
#include"optimizer/cost.h"
1819
#include"optimizer/paths.h"
1920
#include"optimizer/restrictinfo.h"
2021
#include"optimizer/var.h"
@@ -27,7 +28,7 @@ static RestrictInfo *make_restrictinfo_internal(Expr *clause,
2728
staticExpr*make_sub_restrictinfos(Expr*clause,
2829
boolis_pushed_down,
2930
boolvalid_everywhere);
30-
staticbooljoin_clause_is_redundant(Query*root,
31+
staticRestrictInfo*join_clause_is_redundant(Query*root,
3132
RestrictInfo*rinfo,
3233
List*reference_list,
3334
JoinTypejointype);
@@ -317,17 +318,42 @@ remove_redundant_join_clauses(Query *root, List *restrictinfo_list,
317318
{
318319
List*result=NIL;
319320
List*item;
321+
QualCostcost;
322+
323+
/*
324+
* If there are any redundant clauses, we want to eliminate the ones
325+
* that are more expensive in favor of the ones that are less so.
326+
* Run cost_qual_eval() to ensure the eval_cost fields are set up.
327+
*/
328+
cost_qual_eval(&cost,restrictinfo_list);
329+
330+
/*
331+
* We don't have enough knowledge yet to be able to estimate the number
332+
* of times a clause might be evaluated, so it's hard to weight the
333+
* startup and per-tuple costs appropriately. For now just weight 'em
334+
* the same.
335+
*/
336+
#defineCLAUSECOST(r) ((r)->eval_cost.startup + (r)->eval_cost.per_tuple)
320337

321338
foreach(item,restrictinfo_list)
322339
{
323340
RestrictInfo*rinfo= (RestrictInfo*)lfirst(item);
341+
RestrictInfo*prevrinfo;
324342

325-
/* drop it if redundant with any prior clause */
326-
if (join_clause_is_redundant(root,rinfo,result,jointype))
327-
continue;
328-
329-
/* otherwise, add it to result list */
330-
result=lappend(result,rinfo);
343+
/* is it redundant with any prior clause? */
344+
prevrinfo=join_clause_is_redundant(root,rinfo,result,jointype);
345+
if (prevrinfo==NULL)
346+
{
347+
/* no, so add it to result list */
348+
result=lappend(result,rinfo);
349+
}
350+
elseif (CLAUSECOST(rinfo)<CLAUSECOST(prevrinfo))
351+
{
352+
/* keep this one, drop the previous one */
353+
result=lremove(prevrinfo,result);
354+
result=lappend(result,rinfo);
355+
}
356+
/* else, drop this one */
331357
}
332358

333359
returnresult;
@@ -361,7 +387,7 @@ select_nonredundant_join_clauses(Query *root,
361387
RestrictInfo*rinfo= (RestrictInfo*)lfirst(item);
362388

363389
/* drop it if redundant with any reference clause */
364-
if (join_clause_is_redundant(root,rinfo,reference_list,jointype))
390+
if (join_clause_is_redundant(root,rinfo,reference_list,jointype)!=NULL)
365391
continue;
366392

367393
/* otherwise, add it to result list */
@@ -373,7 +399,8 @@ select_nonredundant_join_clauses(Query *root,
373399

374400
/*
375401
* join_clause_is_redundant
376-
*Returns true if rinfo is redundant with any clause in reference_list.
402+
*If rinfo is redundant with any clause in reference_list,
403+
*return one such clause; otherwise return NULL.
377404
*
378405
* This is the guts of both remove_redundant_join_clauses and
379406
* select_nonredundant_join_clauses. See the docs above for motivation.
@@ -398,49 +425,53 @@ select_nonredundant_join_clauses(Query *root,
398425
* then they're not really redundant, because one constrains the
399426
* joined rows after addition of null fill rows, and the other doesn't.
400427
*/
401-
staticbool
428+
staticRestrictInfo*
402429
join_clause_is_redundant(Query*root,
403430
RestrictInfo*rinfo,
404431
List*reference_list,
405432
JoinTypejointype)
406433
{
434+
List*refitem;
435+
407436
/* always consider exact duplicates redundant */
408-
/* XXX would it be sufficient to use ptrMember here? */
409-
if (member(rinfo,reference_list))
410-
return true;
437+
foreach(refitem,reference_list)
438+
{
439+
RestrictInfo*refrinfo= (RestrictInfo*)lfirst(refitem);
440+
441+
if (equal(rinfo,refrinfo))
442+
returnrefrinfo;
443+
}
411444

412445
/* check for redundant merge clauses */
413446
if (rinfo->mergejoinoperator!=InvalidOid)
414447
{
415-
boolredundant= false;
416-
List*refitem;
417-
418448
/* do the cheap test first: is it a "var = const" clause? */
419449
if (bms_is_empty(rinfo->left_relids)||
420450
bms_is_empty(rinfo->right_relids))
421-
returnfalse;/* var = const, so not redundant */
451+
returnNULL;/* var = const, so not redundant */
422452

423453
cache_mergeclause_pathkeys(root,rinfo);
424454

425455
foreach(refitem,reference_list)
426456
{
427457
RestrictInfo*refrinfo= (RestrictInfo*)lfirst(refitem);
428458

429-
if (refrinfo->mergejoinoperator!=InvalidOid&&
430-
rinfo->left_pathkey==refrinfo->left_pathkey&&
431-
rinfo->right_pathkey==refrinfo->right_pathkey&&
432-
(rinfo->is_pushed_down==refrinfo->is_pushed_down||
433-
!IS_OUTER_JOIN(jointype)))
459+
if (refrinfo->mergejoinoperator!=InvalidOid)
434460
{
435-
redundant= true;
436-
break;
461+
cache_mergeclause_pathkeys(root,refrinfo);
462+
463+
if (rinfo->left_pathkey==refrinfo->left_pathkey&&
464+
rinfo->right_pathkey==refrinfo->right_pathkey&&
465+
(rinfo->is_pushed_down==refrinfo->is_pushed_down||
466+
!IS_OUTER_JOIN(jointype)))
467+
{
468+
/* Yup, it's redundant */
469+
returnrefrinfo;
470+
}
437471
}
438472
}
439-
440-
if (redundant)
441-
return true;/* var = var, so redundant */
442473
}
443474

444475
/* otherwise, not redundant */
445-
returnfalse;
476+
returnNULL;
446477
}

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