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Document that CLUSTER breaks MVCC visibility rules.

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(Not needed in cvs head, because CLUSTER itself is fixed there)

Heikki Linnakangas
This commit is contained in:
Magnus Hagander 2007-05-13 16:04:40 +00:00
parent 1e7f0c3a14
commit 38e6aea5a7
1 changed files with 12 additions and 1 deletions
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doc/src/sgml/ref/cluster.sgml
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@ -1,5 +1,5 @@
<!-- <!--
$PostgreSQL: pgsql/doc/src/sgml/ref/cluster.sgml,v 1.38 2006/11/04 19:03:51 tgl Exp $ $PostgreSQL: pgsql/doc/src/sgml/ref/cluster.sgml,v 1.38.2.1 2007/05/13 16:04:40 mha Exp $
PostgreSQL documentation PostgreSQL documentation
--> -->
@ -99,6 +99,17 @@ CLUSTER
<refsect1> <refsect1>
<title>Notes</title> <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> <para>
In cases where you are accessing single rows randomly In cases where you are accessing single rows randomly
within a table, the actual order of the data in the within a table, the actual order of the data in the