Skip opfamily check in eclass_matches_any_index() when the index isn't a

btree.  We can't easily tell whether clauses generated from the equivalence
class could be used with such an index, so just assume that they might be.
This bit of over-optimization prevented use of non-btree indexes for nestloop
inner indexscans, in any case where the join uses an equality operator that
is also a btree operator --- which in particular is typically true for hash
indexes.  Noted while trying to test the current hash index patch.

diff --git a/src/backend/optimizer/path/indxpath.c b/src/backend/optimizer/path/indxpath.c
index 92a3fb59d1b33b252186d74ae16f560f2b213d5c..297c50389fb4bc5dcfebbcb582d849bfc7b32655 100644 (file)
--- a/src/backend/optimizer/path/indxpath.c
+++ b/src/backend/optimizer/path/indxpath.c
@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/optimizer/path/indxpath.c,v 1.232 2008/08/14 18:47:59 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/optimizer/path/indxpath.c,v 1.233 2008/09/12 14:56:13 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1584,7 +1584,18 @@ eclass_matches_any_index(EquivalenceClass *ec, EquivalenceMember *em,
                {
                        Oid                     curFamily = families[0];
 
-                       if (list_member_oid(ec->ec_opfamilies, curFamily) &&
+                       /*
+                        * If it's a btree index, we can reject it if its opfamily isn't
+                        * compatible with the EC, since no clause generated from the
+                        * EC could be used with the index.  For non-btree indexes,
+                        * we can't easily tell whether clauses generated from the EC
+                        * could be used with the index, so only check for expression
+                        * match.  This might mean we return "true" for a useless index,
+                        * but that will just cause some wasted planner cycles; it's
+                        * better than ignoring useful indexes.
+                        */
+                       if ((index->relam != BTREE_AM_OID ||
+                                list_member_oid(ec->ec_opfamilies, curFamily)) &&
                                match_index_to_operand((Node *) em->em_expr, indexcol, index))
                                return true;