From 92c0bf09603bc965816ebb589e28a44dfbb9e8f7 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Fri, 23 Nov 2007 19:57:44 +0000
Subject: [PATCH] Avoid uselessly building a duplicate of the original clause
in trivial cases where the EquivalenceClass machinery is unable to deduce
anything more from a simple "var = const" qual clause. There are probably
some more cases where this could be done, but this seems to take care of most
of the added overhead for 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 to
build_implied_join_equality, resulting in RestrictInfos with the wrong
required_relids. This mistake was masked in typical cases since the bogus
RestrictInfos would never have escaped from the EquivalenceClass machinery,
but I think there might be corner cases involving "broken" ECs where there
would have been a visible failure even without the new optimization. In any
case the code was certainly not operating as intended.
---
src/backend/optimizer/path/equivclass.c | 37 +++++++++++++++++++++----
1 file changed, 32 insertions(+), 5 deletions(-)
diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c
index 5d92c7c8df2..bf93fc2e667 100644
--- a/src/backend/optimizer/path/equivclass.c
+++ b/src/backend/optimizer/path/equivclass.c
@@ -10,7 +10,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/optimizer/path/equivclass.c,v 1.6 2007/11/15 22:25:15 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/optimizer/path/equivclass.c,v 1.7 2007/11/23 19:57:44 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -559,6 +559,25 @@ generate_base_implied_equalities_const(PlannerInfo *root,
EquivalenceMember *const_em = NULL;
ListCell *lc;
+ /*
+ * In the trivial case where we just had one "var = const" clause,
+ * push the original clause back into the main planner machinery. There
+ * is nothing to be gained by doing it differently, and we save the
+ * effort to re-build and re-analyze an equality clause that will be
+ * exactly equivalent to the old one.
+ */
+ if (list_length(ec->ec_members) == 2 &&
+ list_length(ec->ec_sources) == 1)
+ {
+ RestrictInfo *restrictinfo = (RestrictInfo *) linitial(ec->ec_sources);
+
+ if (bms_membership(restrictinfo->required_relids) != BMS_MULTIPLE)
+ {
+ distribute_restrictinfo_to_rels(root, restrictinfo);
+ return;
+ }
+ }
+
/* Find the constant member to use */
foreach(lc, ec->ec_members)
{
@@ -1047,7 +1066,8 @@ create_join_clause(PlannerInfo *root,
rinfo = build_implied_join_equality(opno,
leftem->em_expr,
rightem->em_expr,
- ec->ec_relids);
+ bms_union(leftem->em_relids,
+ rightem->em_relids));
/* Mark the clause as redundant, or not */
rinfo->parent_ec = parent_ec;
@@ -1165,6 +1185,7 @@ reconsider_outer_join_clause(PlannerInfo *root, RestrictInfo *rinfo,
Oid left_type,
right_type,
inner_datatype;
+ Relids inner_relids;
ListCell *lc1;
/* Extract needed info from the clause */
@@ -1176,12 +1197,14 @@ reconsider_outer_join_clause(PlannerInfo *root, RestrictInfo *rinfo,
outervar = (Expr *) get_leftop(rinfo->clause);
innervar = (Expr *) get_rightop(rinfo->clause);
inner_datatype = right_type;
+ inner_relids = rinfo->right_relids;
}
else
{
outervar = (Expr *) get_rightop(rinfo->clause);
innervar = (Expr *) get_leftop(rinfo->clause);
inner_datatype = left_type;
+ inner_relids = rinfo->left_relids;
}
/* Scan EquivalenceClasses for a match to outervar */
@@ -1237,7 +1260,7 @@ reconsider_outer_join_clause(PlannerInfo *root, RestrictInfo *rinfo,
newrinfo = build_implied_join_equality(eq_op,
innervar,
cur_em->em_expr,
- cur_ec->ec_relids);
+ inner_relids);
if (process_equivalence(root, newrinfo, true))
match = true;
}
@@ -1268,6 +1291,8 @@ reconsider_full_join_clause(PlannerInfo *root, RestrictInfo *rinfo)
Expr *rightvar;
Oid left_type,
right_type;
+ Relids left_relids,
+ right_relids;
ListCell *lc1;
/* Extract needed info from the clause */
@@ -1276,6 +1301,8 @@ reconsider_full_join_clause(PlannerInfo *root, RestrictInfo *rinfo)
rightvar = (Expr *) get_rightop(rinfo->clause);
op_input_types(((OpExpr *) rinfo->clause)->opno,
&left_type, &right_type);
+ left_relids = rinfo->left_relids;
+ right_relids = rinfo->right_relids;
foreach(lc1, root->eq_classes)
{
@@ -1357,7 +1384,7 @@ reconsider_full_join_clause(PlannerInfo *root, RestrictInfo *rinfo)
newrinfo = build_implied_join_equality(eq_op,
leftvar,
cur_em->em_expr,
- cur_ec->ec_relids);
+ left_relids);
if (process_equivalence(root, newrinfo, true))
matchleft = true;
}
@@ -1369,7 +1396,7 @@ reconsider_full_join_clause(PlannerInfo *root, RestrictInfo *rinfo)
newrinfo = build_implied_join_equality(eq_op,
rightvar,
cur_em->em_expr,
- cur_ec->ec_relids);
+ right_relids);
if (process_equivalence(root, newrinfo, true))
matchright = true;
}
--
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