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PostgreSQL documentation

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</refsynopsisdivinfo>

<synopsis>

CLUSTER <replaceable class="PARAMETER">indexname</replaceable> ON <replaceable class="PARAMETER">tablename</replaceable>

CLUSTER <replaceable class="PARAMETER">tablename</replaceable>

CLUSTER ALL

</synopsis>

<refsect2 id="R2-SQL-CLUSTER-1">

periodically re-cluster by issuing the command again.

</para>

<para>

When a table is clustered, <productname>PostgreSQL</productname>

remembers on which index it was clustered. In calls to

<command>CLUSTER <replaceable class="parameter">tablename</replaceable></command>,

the table is clustered on the same index that it was clustered before.

</para>

<para>

In calls to <command>CLUSTER ALL</command>, all the tables in the database

that the calling user owns are clustered using the saved information. This

form of <command>CLUSTER</command> cannot be called from inside a

transaction or function.

</para>

<refsect2 id="R2-SQL-CLUSTER-3">

<refsect2info>

<date>1998-09-08</date>

</para>

<para>

CLUSTER preserves GRANT, inheritance, index, foreign key, and other

ancillary information about the table.

<command>CLUSTER</command> preserves GRANT, inheritance, index, foreign

key, and other ancillary information about the table.

</para>

<para>

Because <command>CLUSTER</command> remembers the clustering information,

one can cluster the tables one wants clustered manually the first time, and

setup a timed event similar to <command>VACUUM</command> so that the tables

are periodically and automatically clustered.

</para>

<para>

<programlisting>

CLUSTER emp_ind ON emp;

</programlisting>

<para>

Cluster the employees relation using the same index that was used before:

</para>

<programlisting>

CLUSTER emp;

</programlisting>

<para>

Cluster all the tables on the database that have previously been clustered:

</para>

<programlisting>

CLUSTER ALL;

</programlisting>

</refsect1>

<refsect1 id="R1-SQL-CLUSTER-3">