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.