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authorMagnus Hagander2007-05-13 16:04:22 +0000
committerMagnus Hagander2007-05-13 16:04:22 +0000
commit7ee0498772e11631f9da2d8dd68f62843f7d651b (patch)
treec66025bf242f90f9bc683a8345d737952314e1bd
parente449e1912485dd3f1dc74471237f79e5e56e7518 (diff)
Document that CLUSTER breaks MVCC visibility rules.
(Not needed in cvs head, because CLUSTER itself is fixed there) Heikki Linnakangas
-rw-r--r--doc/src/sgml/ref/cluster.sgml13
1 files changed, 12 insertions, 1 deletions
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
-->
@@ -100,6 +100,17 @@ CLUSTER
<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
table is unimportant. However, if you tend to access some