From 46a0eee3006b11a15b73426c8146ed5ab32e1d62 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sun, 28 Aug 2005 22:47:20 +0000
Subject: [PATCH] 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.
---
src/backend/executor/nodeBitmapAnd.c | 12 +++++++++++-
src/backend/nodes/tidbitmap.c | 11 ++++++++++-
src/backend/optimizer/path/indxpath.c | 7 ++++++-
src/include/nodes/tidbitmap.h | 4 +++-
4 files changed, 30 insertions(+), 4 deletions(-)
diff --git a/src/backend/executor/nodeBitmapAnd.c b/src/backend/executor/nodeBitmapAnd.c
index 1d5d94fc3f8..939062d4d6c 100644
--- 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 777bf6482d2..e36a8d9806a 100644
--- 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 $
*
*-------------------------------------------------------------------------
*/
@@ -510,6 +510,15 @@ 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
*
diff --git a/src/backend/optimizer/path/indxpath.c b/src/backend/optimizer/path/indxpath.c
index bd0b09fcfe9..c689d1461e9 100644
--- 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 2c90c01d815..ea5673e6f27 100644
--- 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);
--
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