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<TITLE>CLUSTER(SQL) manual page</TITLE>
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<A HREF="sql.html">SQL Reference Contents</A>
<H2><A NAME="sect0" HREF="#toc0">NAME </A></H2>
cluster - give storage clustering advice to Postgres
<H2><A NAME="sect1" HREF="#toc1">SYNOPSIS </A></H2>
<B>cluster
</B> indexname <B>on </B> attname <BR>
<H2><A NAME="sect2" HREF="#toc2">DESCRIPTION </A></H2>
This command instructs Postgres to
cluster the class specified by <I>classname</I> approximately based on the index
specified by <I>indexname.</I> The index must already have been defined on <I>classname.</I>
<P>
When a class is clustered, it is physically reordered based on the index
information. The clustering is static. In other words, if the class is
updated, it may become unclustered. No attempt is made to keep new instances
or updated tuples clustered. If desired, the user can recluster manually
by issuing the command again. <P>
The table is actually copied to temporary
table in index order, then renamed back to the original name. For this
reason, all grant permissions and other indexes are lost when cluster
is performed.
<H2><A NAME="sect3" HREF="#toc3">EXAMPLE </A></H2>
/* <BR>
* cluster employees in based on its salary
attribute <BR>
*/ <BR>
create index emp_ind on emp using btree (salary int4_ops);
<BR>
<P>
cluster emp_ind on emp <BR>
<P>
<P>
<HR><P>
<A NAME="toc"><B>Table of Contents</B></A><P>
<UL>
<LI><A NAME="toc0" HREF="#sect0">NAME</A></LI>
<LI><A NAME="toc1" HREF="#sect1">SYNOPSIS</A></LI>
<LI><A NAME="toc2" HREF="#sect2">DESCRIPTION</A></LI>
<LI><A NAME="toc3" HREF="#sect3">EXAMPLE</A></LI>
</UL>
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