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Commit92c0bf0

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Avoid uselessly building a duplicate of the original clause in trivial cases
where the EquivalenceClass machinery is unable to deduce anything more from asimple "var = const" qual clause. There are probably some more cases wherethis could be done, but this seems to take care of most of the added overheadfor simple queries. Per gripe from Guillaume Smet.In passing, fix a problem that was exposed by this change:reconsider_outer_join_clause and friends were passing the wrong relids tobuild_implied_join_equality, resulting in RestrictInfos with the wrongrequired_relids. This mistake was masked in typical cases since the bogusRestrictInfos would never have escaped from the EquivalenceClass machinery,but I think there might be corner cases involving "broken" ECs where therewould have been a visible failure even without the new optimization. In anycase the code was certainly not operating as intended.
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‎src/backend/optimizer/path/equivclass.c

Lines changed: 32 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -10,7 +10,7 @@
1010
* Portions Copyright (c) 1994, Regents of the University of California
1111
*
1212
* IDENTIFICATION
13-
* $PostgreSQL: pgsql/src/backend/optimizer/path/equivclass.c,v 1.6 2007/11/15 22:25:15 momjian Exp $
13+
* $PostgreSQL: pgsql/src/backend/optimizer/path/equivclass.c,v 1.7 2007/11/23 19:57:44 tgl Exp $
1414
*
1515
*-------------------------------------------------------------------------
1616
*/
@@ -559,6 +559,25 @@ generate_base_implied_equalities_const(PlannerInfo *root,
559559
EquivalenceMember*const_em=NULL;
560560
ListCell*lc;
561561

562+
/*
563+
* In the trivial case where we just had one "var = const" clause,
564+
* push the original clause back into the main planner machinery. There
565+
* is nothing to be gained by doing it differently, and we save the
566+
* effort to re-build and re-analyze an equality clause that will be
567+
* exactly equivalent to the old one.
568+
*/
569+
if (list_length(ec->ec_members)==2&&
570+
list_length(ec->ec_sources)==1)
571+
{
572+
RestrictInfo*restrictinfo= (RestrictInfo*)linitial(ec->ec_sources);
573+
574+
if (bms_membership(restrictinfo->required_relids)!=BMS_MULTIPLE)
575+
{
576+
distribute_restrictinfo_to_rels(root,restrictinfo);
577+
return;
578+
}
579+
}
580+
562581
/* Find the constant member to use */
563582
foreach(lc,ec->ec_members)
564583
{
@@ -1047,7 +1066,8 @@ create_join_clause(PlannerInfo *root,
10471066
rinfo=build_implied_join_equality(opno,
10481067
leftem->em_expr,
10491068
rightem->em_expr,
1050-
ec->ec_relids);
1069+
bms_union(leftem->em_relids,
1070+
rightem->em_relids));
10511071

10521072
/* Mark the clause as redundant, or not */
10531073
rinfo->parent_ec=parent_ec;
@@ -1165,6 +1185,7 @@ reconsider_outer_join_clause(PlannerInfo *root, RestrictInfo *rinfo,
11651185
Oidleft_type,
11661186
right_type,
11671187
inner_datatype;
1188+
Relidsinner_relids;
11681189
ListCell*lc1;
11691190

11701191
/* Extract needed info from the clause */
@@ -1176,12 +1197,14 @@ reconsider_outer_join_clause(PlannerInfo *root, RestrictInfo *rinfo,
11761197
outervar= (Expr*)get_leftop(rinfo->clause);
11771198
innervar= (Expr*)get_rightop(rinfo->clause);
11781199
inner_datatype=right_type;
1200+
inner_relids=rinfo->right_relids;
11791201
}
11801202
else
11811203
{
11821204
outervar= (Expr*)get_rightop(rinfo->clause);
11831205
innervar= (Expr*)get_leftop(rinfo->clause);
11841206
inner_datatype=left_type;
1207+
inner_relids=rinfo->left_relids;
11851208
}
11861209

11871210
/* Scan EquivalenceClasses for a match to outervar */
@@ -1237,7 +1260,7 @@ reconsider_outer_join_clause(PlannerInfo *root, RestrictInfo *rinfo,
12371260
newrinfo=build_implied_join_equality(eq_op,
12381261
innervar,
12391262
cur_em->em_expr,
1240-
cur_ec->ec_relids);
1263+
inner_relids);
12411264
if (process_equivalence(root,newrinfo, true))
12421265
match= true;
12431266
}
@@ -1268,6 +1291,8 @@ reconsider_full_join_clause(PlannerInfo *root, RestrictInfo *rinfo)
12681291
Expr*rightvar;
12691292
Oidleft_type,
12701293
right_type;
1294+
Relidsleft_relids,
1295+
right_relids;
12711296
ListCell*lc1;
12721297

12731298
/* Extract needed info from the clause */
@@ -1276,6 +1301,8 @@ reconsider_full_join_clause(PlannerInfo *root, RestrictInfo *rinfo)
12761301
rightvar= (Expr*)get_rightop(rinfo->clause);
12771302
op_input_types(((OpExpr*)rinfo->clause)->opno,
12781303
&left_type,&right_type);
1304+
left_relids=rinfo->left_relids;
1305+
right_relids=rinfo->right_relids;
12791306

12801307
foreach(lc1,root->eq_classes)
12811308
{
@@ -1357,7 +1384,7 @@ reconsider_full_join_clause(PlannerInfo *root, RestrictInfo *rinfo)
13571384
newrinfo=build_implied_join_equality(eq_op,
13581385
leftvar,
13591386
cur_em->em_expr,
1360-
cur_ec->ec_relids);
1387+
left_relids);
13611388
if (process_equivalence(root,newrinfo, true))
13621389
matchleft= true;
13631390
}
@@ -1369,7 +1396,7 @@ reconsider_full_join_clause(PlannerInfo *root, RestrictInfo *rinfo)
13691396
newrinfo=build_implied_join_equality(eq_op,
13701397
rightvar,
13711398
cur_em->em_expr,
1372-
cur_ec->ec_relids);
1399+
right_relids);
13731400
if (process_equivalence(root,newrinfo, true))
13741401
matchright= true;
13751402
}

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