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.

diff --git a/src/backend/optimizer/path/clausesel.c b/src/backend/optimizer/path/clausesel.c
index f5ee929c56e0497609e5d7186602353f0d4b9d25..dd4a27b96cc0cf04dd7db2f2400c8676dc04c247 100644 (file)
--- 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