Avoid useless work during set_plain_rel_pathlist() when the relation

will be excluded by constraint exclusion anyway.  Greg Stark

diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index 7aa2bd7e6fb2c050aefce6853fe93da4ea5ddee9..0d87291025f5e08f7b9c447cb8db8033c74e221c 100644 (file)
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *   $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.161 2007/02/22 22:00:23 tgl Exp $
+ *   $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.162 2007/04/21 06:18:52 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -196,20 +196,6 @@ set_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, Index rti)
 static void
 set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
 {
-   /* Mark rel with estimated output rows, width, etc */
-   set_baserel_size_estimates(root, rel);
-
-   /* Test any partial indexes of rel for applicability */
-   check_partial_indexes(root, rel);
-
-   /*
-    * Check to see if we can extract any restriction conditions from join
-    * quals that are OR-of-AND structures.  If so, add them to the rel's
-    * restriction list, and recompute the size estimates.
-    */
-   if (create_or_index_quals(root, rel))
-       set_baserel_size_estimates(root, rel);
-
    /*
     * If we can prove we don't need to scan the rel via constraint exclusion,
     * set up a single dummy path for it.  (Rather than inventing a special
@@ -217,8 +203,9 @@ set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
     */
    if (relation_excluded_by_constraints(rel, rte))
    {
-       /* Reset output-rows estimate to 0 */
+       /* Set dummy size estimates --- we leave attr_widths[] as zeroes */
        rel->rows = 0;
+       rel->width = 0;
 
        add_path(rel, (Path *) create_append_path(rel, NIL));
 
@@ -228,6 +215,20 @@ set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
        return;
    }
 
+   /* Mark rel with estimated output rows, width, etc */
+   set_baserel_size_estimates(root, rel);
+
+   /* Test any partial indexes of rel for applicability */
+   check_partial_indexes(root, rel);
+
+   /*
+    * Check to see if we can extract any restriction conditions from join
+    * quals that are OR-of-AND structures.  If so, add them to the rel's
+    * restriction list, and recompute the size estimates.
+    */
+   if (create_or_index_quals(root, rel))
+       set_baserel_size_estimates(root, rel);
+
    /*
     * Generate paths and add them to the rel's pathlist.
     *
@@ -369,7 +370,8 @@ set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
        /*
         * Propagate size information from the child back to the parent. For
         * simplicity, we use the largest widths from any child as the parent
-        * estimates.
+        * estimates.  (If you want to change this, beware of child
+        * attr_widths[] entries that haven't been set and are still 0.)
         */
        rel->rows += childrel->rows;
        if (childrel->width > rel->width)