Further tweaking of indexscan cost estimates.

diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index 37b4dfc42e7a28ae60d777fc53e0a0fdcc6b48e7..f6bdcb828b92d6c97f4691cac6d0bb01fddcd989 100644 (file)
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -42,7 +42,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *       $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.55 2000/03/30 00:53:29 tgl Exp $
+ *       $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.56 2000/04/09 04:31:36 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -262,9 +262,12 @@ cost_index(Path *path, Query *root,
         * effect.  Would be nice to do better someday.
         */
 
-       tuples_fetched = ceil(indexSelectivity * baserel->tuples);
+       tuples_fetched = indexSelectivity * baserel->tuples;
+       /* Don't believe estimates less than 1... */
+       if (tuples_fetched < 1.0)
+               tuples_fetched = 1.0;
 
-       if (tuples_fetched > 0 && baserel->pages > 0)
+       if (baserel->pages > 0)
                pages_fetched = ceil(baserel->pages *
                                                         log(tuples_fetched / baserel->pages + 1.0));
        else

diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c
index 0cd408ed78fc77e4321d125d40e1dd187b825957..7e03b10d43105615d9befae1faa2f69e2d5211d6 100644 (file)
--- a/src/backend/utils/adt/selfuncs.c
+++ b/src/backend/utils/adt/selfuncs.c
@@ -15,7 +15,7 @@
  *
  *
  * IDENTIFICATION
- *       $Header: /cvsroot/pgsql/src/backend/utils/adt/selfuncs.c,v 1.62 2000/03/30 00:53:30 tgl Exp $
+ *       $Header: /cvsroot/pgsql/src/backend/utils/adt/selfuncs.c,v 1.63 2000/04/09 04:31:37 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -902,10 +902,19 @@ genericcostestimate(Query *root, RelOptInfo *rel,
                                                                                           lfirsti(rel->relids));
 
        /* Estimate the number of index tuples that will be visited */
-       numIndexTuples = ceil(*indexSelectivity * index->tuples);
+       numIndexTuples = *indexSelectivity * index->tuples;
 
        /* Estimate the number of index pages that will be retrieved */
-       numIndexPages = ceil(*indexSelectivity * index->pages);
+       numIndexPages = *indexSelectivity * index->pages;
+
+       /*
+        * Always estimate at least one tuple and page are touched,
+        * even when indexSelectivity estimate is tiny.
+        */
+       if (numIndexTuples < 1.0)
+               numIndexTuples = 1.0;
+       if (numIndexPages < 1.0)
+               numIndexPages = 1.0;
 
        /*
         * Compute the index access cost.