From fd267c1ebc363ae6b1bf586794fa5cc9e8cca43c Mon Sep 17 00:00:00 2001
From: Tom Lane
Date: Sat, 11 Feb 2006 23:31:34 +0000
Subject: Skip ambulkdelete scan if there's nothing to delete and the index is
 not partial.  None of the existing AMs do anything useful except counting
 tuples when there's nothing to delete, and we can get a tuple count from the
 heap as long as it's not a partial index.  (hash actually can skip anyway
 because it maintains a tuple count in the index metapage.) GIST is not
 currently able to exploit this optimization because, due to failure to index
 NULLs, GIST is always effectively partial.  Possibly we should fix that
 sometime. Simon Riggs w/ some review by Tom Lane.

---
 doc/src/sgml/indexam.sgml | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

(limited to 'doc/src')

diff --git a/doc/src/sgml/indexam.sgml b/doc/src/sgml/indexam.sgml
index 7480c98a15b..d766467bdb4 100644
--- a/doc/src/sgml/indexam.sgml
+++ b/doc/src/sgml/indexam.sgml
@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/indexam.sgml,v 2.7 2005/11/04 23:14:00 petere Exp $
+$PostgreSQL: pgsql/doc/src/sgml/indexam.sgml,v 2.8 2006/02/11 23:31:32 tgl Exp $
 -->
 
 <chapter id="indexam">
@@ -200,6 +200,12 @@ ambulkdelete (Relation indexRelation,
    struct containing statistics about the effects of the deletion operation.
   </para>
 
+  <para>
+   If <literal>callback_state</> is NULL then no tuples are to be deleted.
+   The index AM may choose to optimize this case (eg by not scanning the
+   index) but it is still expected to deliver accurate statistics.
+  </para>
+
   <para>
 <programlisting>
 IndexBulkDeleteResult *
-- 
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