99 *
1010 *
1111 * IDENTIFICATION
12- * $PostgreSQL: pgsql/src/backend/optimizer/path/indxpath.c,v 1.173 2005/04/11 23:06:55 tgl Exp $
12+ * $PostgreSQL: pgsql/src/backend/optimizer/path/indxpath.c,v 1.174 2005/04/20 21:48:04 tgl Exp $
1313 *
1414 *-------------------------------------------------------------------------
1515 */
@@ -146,11 +146,16 @@ create_index_paths(Query *root, RelOptInfo *rel)
146146 * 2. Compute pathkeys describing index's ordering, if any, then
147147 * see how many of them are actually useful for this query.
148148 */
149- index_pathkeys = build_index_pathkeys (root ,index ,
150- ForwardScanDirection );
151- index_is_ordered = (index_pathkeys != NIL );
152- useful_pathkeys = truncate_useless_pathkeys (root ,rel ,
153- index_pathkeys );
149+ index_is_ordered = OidIsValid (index -> ordering [0 ]);
150+ if (index_is_ordered )
151+ {
152+ index_pathkeys = build_index_pathkeys (root ,index ,
153+ ForwardScanDirection );
154+ useful_pathkeys = truncate_useless_pathkeys (root ,rel ,
155+ index_pathkeys );
156+ }
157+ else
158+ useful_pathkeys = NIL ;
154159
155160/*
156161 * 3. Generate an indexscan path if there are relevant restriction
@@ -160,10 +165,15 @@ create_index_paths(Query *root, RelOptInfo *rel)
160165 * If there is a predicate, consider it anyway since the index
161166 * predicate has already been found to match the query. The
162167 * selectivity of the predicate might alone make the index useful.
168+ *
169+ * Note: not all index AMs support scans with no restriction clauses.
170+ * We assume here that the AM does so if and only if it supports
171+ * ordered scans. (It would probably be better if there were a
172+ * specific flag for this in pg_am, but there's not.)
163173 */
164174if (restrictclauses != NIL ||
165175useful_pathkeys != NIL ||
166- index -> indpred != NIL )
176+ ( index -> indpred != NIL && index_is_ordered ) )
167177add_path (rel , (Path * )
168178create_index_path (root ,index ,
169179restrictclauses ,