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.

1 files changed, 13 insertions, 2 deletions

diff --git a/src/backend/optimizer/path/indxpath.c b/src/backend/optimizer/path/indxpath.c
index 8a2e808cc30..3100c92d3d8 100644
--- 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 1.227 2008/02/07 17:53:53 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/path/indxpath.c,v 1.227.2.1 2008/09/12 14:56:19 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;