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PostgreSQL documentation

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<refsynopsisdiv>

<synopsis>

CLUSTER <replaceable class="PARAMETER">tablename</replaceable>[ USING <replaceable class="PARAMETER">indexname</replaceable>]

CLUSTER <replaceable class="PARAMETER">tablename</replaceable><optional> USING <replaceable class="PARAMETER">indexname</replaceable></optional>

CLUSTER

</synopsis>

</refsynopsisdiv>

based on the index information. Clustering is a one-time operation:

when the table is subsequently updated, the changes are

not clustered. That is, no attempt is made to store new or

updated rows according to their index order. If one wishes, one can

periodically recluster by issuing the command again.

updated rows according to their index order. (If one wishes, one can

periodically recluster by issuing the command again. Also, setting

the table's FILLFACTOR storage parameter to less than 100% can aid

in preserving cluster ordering during updates, since updated rows

are preferentially kept on the same page.)

</para>

<para>

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

remembersonwhich index it was clustered. The form

remembers which index it was clustered by. The form

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

reclusters the tableon the same indexthat it was clustered before.

reclusters the tableusing the same indexas before.

</para>

<para>

<command>CLUSTER</command> without any parameter reclusters all the tables

in the

current database that the calling user owns, or all tables if called

by a superuser. (Never-clustered tables are not included.) This

<command>CLUSTER</command> without any parameter reclusters all the

previously-clustered tables in the current database that the calling user

owns, or all such tables if called by a superuser. This

form of <command>CLUSTER</command> cannot be executed inside a transaction

block.

</para>

<title>Compatibility</title>

<para>

The syntax:

There is no <command>CLUSTER</command> statement in the SQL standard.

</para>

<para>

The syntax

<synopsis>

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

</synopsis>

is also supported for compatibility with pre-8.3 <productname>PostgreSQL</> installations.

There is no <command>CLUSTER</command> statement in the SQL standard.

is also supported for compatibility with pre-8.3 <productname>PostgreSQL</>

versions.

</para>

</refsect1>