From aca467b9b343dccd52a8c8da74ffcf70559fb468 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 24 Nov 2007 19:08:51 +0000
Subject: [PATCH] Save another little bit of planner overhead on simple
 queries, by having clauselist_selectivity skip some analysis that's useless
 when there's only one clause in the given list.  Actually this can win even
 for not-so-simple queries, because we also apply clauselist_selectivity to
 sublists such as the quals matching an index; which are likely to have only a
 single entry even when the total query is quite complicated.

---
 src/backend/optimizer/path/clausesel.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/backend/optimizer/path/clausesel.c b/src/backend/optimizer/path/clausesel.c
index f5ee929c56e..dd4a27b96cc 100644
--- a/src/backend/optimizer/path/clausesel.c
+++ b/src/backend/optimizer/path/clausesel.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/path/clausesel.c,v 1.87 2007/08/31 23:35:22 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/path/clausesel.c,v 1.88 2007/11/24 19:08:51 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -100,6 +100,14 @@ clauselist_selectivity(PlannerInfo *root,
 	RangeQueryClause *rqlist = NULL;
 	ListCell   *l;
 
+	/*
+	 * If there's exactly one clause, then no use in trying to match up
+	 * pairs, so just go directly to clause_selectivity().
+	 */
+	if (list_length(clauses) == 1)
+		return clause_selectivity(root, (Node *) linitial(clauses),
+								  varRelid, jointype);
+
 	/*
 	 * Initial scan over clauses.  Anything that doesn't look like a potential
 	 * rangequery clause gets multiplied into s1 and forgotten. Anything that
-- 
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