Tweak nodeBitmapAnd to stop evaluating sub-plan scans if it finds it's

got an empty bitmap after any step; the remaining subplans can no longer
affect the result.  Per a suggestion from Ilia Kantor.

diff --git a/src/backend/executor/nodeBitmapAnd.c b/src/backend/executor/nodeBitmapAnd.c
index 1d5d94f..939062d 100644 (file)
--- a/src/backend/executor/nodeBitmapAnd.c
+++ b/src/backend/executor/nodeBitmapAnd.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/executor/nodeBitmapAnd.c,v 1.2 2005/04/20 15:48:36 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/executor/nodeBitmapAnd.c,v 1.3 2005/08/28 22:47:20 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -143,6 +143,16 @@ MultiExecBitmapAnd(BitmapAndState *node)
                        tbm_intersect(result, subresult);
                        tbm_free(subresult);
                }
+
+               /*
+                * If at any stage we have a completely empty bitmap, we can fall
+                * out without evaluating the remaining subplans, since ANDing them
+                * can no longer change the result.  (Note: the fact that indxpath.c
+                * orders the subplans by selectivity should make this case more
+                * likely to occur.)
+                */
+               if (tbm_is_empty(result))
+                       break;
        }
 
        if (result == NULL)

diff --git a/src/backend/nodes/tidbitmap.c b/src/backend/nodes/tidbitmap.c
index 777bf64..e36a8d9 100644 (file)
--- a/src/backend/nodes/tidbitmap.c
+++ b/src/backend/nodes/tidbitmap.c
@@ -23,7 +23,7 @@
  * Copyright (c) 2003-2005, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/nodes/tidbitmap.c,v 1.5 2005/07/24 02:25:26 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/nodes/tidbitmap.c,v 1.6 2005/08/28 22:47:20 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -511,6 +511,15 @@ tbm_intersect_page(TIDBitmap *a, PagetableEntry *apage, const TIDBitmap *b)
 }
 
 /*
+ * tbm_is_empty - is a TIDBitmap completely empty?
+ */
+bool
+tbm_is_empty(const TIDBitmap *tbm)
+{
+       return (tbm->nentries == 0);
+}
+
+/*
  * tbm_begin_iterate - prepare to iterate through a TIDBitmap
  *
  * NB: after this is called, it is no longer allowed to modify the contents

diff --git a/src/backend/optimizer/path/indxpath.c b/src/backend/optimizer/path/indxpath.c
index bd0b09f..c689d14 100644 (file)
--- 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 1.187 2005/07/28 20:26:20 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/optimizer/path/indxpath.c,v 1.188 2005/08/28 22:47:20 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -538,6 +538,11 @@ choose_bitmap_and(PlannerInfo *root, RelOptInfo *rel, List *paths)
         * cases, the partial index will sort before competing non-partial
         * indexes and so it makes the right choice, but perhaps we need to
         * work harder.
+        *
+        * Note: outputting the selected sub-paths in selectivity order is a good
+        * thing even if we weren't using that as part of the selection method,
+        * because it makes the short-circuit case in MultiExecBitmapAnd() more
+        * likely to apply.
         */
 
        /* Convert list to array so we can apply qsort */

diff --git a/src/include/nodes/tidbitmap.h b/src/include/nodes/tidbitmap.h
index 2c90c01..ea5673e 100644 (file)
--- a/src/include/nodes/tidbitmap.h
+++ b/src/include/nodes/tidbitmap.h
@@ -15,7 +15,7 @@
  *
  * Copyright (c) 2003-2005, PostgreSQL Global Development Group
  *
- * $PostgreSQL: pgsql/src/include/nodes/tidbitmap.h,v 1.1 2005/04/17 22:24:02 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/nodes/tidbitmap.h,v 1.2 2005/08/28 22:47:20 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -49,6 +49,8 @@ extern void tbm_add_tuples(TIDBitmap *tbm, const ItemPointer tids, int ntids);
 extern void tbm_union(TIDBitmap *a, const TIDBitmap *b);
 extern void tbm_intersect(TIDBitmap *a, const TIDBitmap *b);
 
+extern bool tbm_is_empty(const TIDBitmap *tbm);
+
 extern void tbm_begin_iterate(TIDBitmap *tbm);
 extern TBMIterateResult *tbm_iterate(TIDBitmap *tbm);