From 7ee0498772e11631f9da2d8dd68f62843f7d651b Mon Sep 17 00:00:00 2001
From: Magnus Hagander <magnus@hagander.net>
Date: Sun, 13 May 2007 16:04:22 +0000
Subject: [PATCH] Document that CLUSTER breaks MVCC visibility rules. (Not
 needed in cvs head, because CLUSTER itself is fixed there)

Heikki Linnakangas
---
 doc/src/sgml/ref/cluster.sgml | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/doc/src/sgml/ref/cluster.sgml b/doc/src/sgml/ref/cluster.sgml
index 12f18623d77..756e1bc569b 100644
--- a/doc/src/sgml/ref/cluster.sgml
+++ b/doc/src/sgml/ref/cluster.sgml
@@ -1,5 +1,5 @@
 <!--
-$Header: /cvsroot/pgsql/doc/src/sgml/ref/cluster.sgml,v 1.30 2003/11/02 12:59:54 petere Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/ref/cluster.sgml,v 1.30.2.1 2007/05/13 16:04:22 mha Exp $
 PostgreSQL documentation
 -->
 
@@ -99,6 +99,17 @@ CLUSTER
  <refsect1>
   <title>Notes</title>
 
+   <para>
+    <command>CLUSTER</command> loses all visibility information of tuples,
+    which makes the table look empty to any snapshot that was taken
+    before the <command>CLUSTER</command> command finished. That makes
+    <command>CLUSTER</command> unsuitable for applications where
+    transactions that access the table being clustered are run concurrently
+    with <command>CLUSTER</command>. This is most visible with serializable
+    transactions, because they take only one snapshot at the beginning of the
+    transaction, but read-committed transactions are also affected.
+   </para>
+
    <para>
     In cases where you are accessing single rows randomly
     within a table, the actual order of the data in the