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Minor editorialization on CLUSTER reference page.

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Tom Lane 2007-04-08 02:07:35 +00:00
parent 7b78474da3
commit e51ac1b899
1 changed files with 19 additions and 13 deletions
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32
doc/src/sgml/ref/cluster.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/cluster.sgml,v 1.41 2007/04/08 00:26:33 momjian Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/cluster.sgml,v 1.42 2007/04/08 02:07:35 tgl Exp $
PostgreSQL documentation
-->
@ -20,7 +20,7 @@ PostgreSQL documentation
<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>
@ -43,22 +43,24 @@ CLUSTER
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>
remembers on which 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 table on the same index that it was clustered before.
reclusters the table using the same index as 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>
@ -197,12 +199,16 @@ CLUSTER;
<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>