<!--
-$Header: /cvsroot/pgsql/doc/src/sgml/maintenance.sgml,v 1.12 2002/03/06 06:44:31 momjian Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/maintenance.sgml,v 1.13 2002/06/13 04:36:50 momjian Exp $
-->
<chapter id="maintenance">
</sect2>
</sect1>
+ <sect1 id="diskspace-maintenance">
+ <title>Disk Space Maintenance</title>
+
+ <indexterm zone="diskspace-maintenance">
+ <primary>disk space</primary>
+ </indexterm>
+
+ <para>
+ Each table has a primary heap disk file where most of the data is
+ stored. To store long column values, there is also a
+ <acronym>TOAST</> file associated with the table, named based on the
+ table's oid (actually pg_class.relfilenode), and an index on the
+ <acronym>TOAST</> table. There also may be indexes associated with
+ the base table.
+ </para>
+
+ <para>
+ You can monitor disk space from two places; from inside
+ <application>psql</> and from the command line using
+ <application>contrib/oid2name</>. Using <application>psql</> you can
+ issue queries to see the disk usage for any table:
+<programlisting>
+play=# SELECT relfilenode, relpages
+play-# FROM pg_class
+play-# WHERE relname = 'customer';
+ relfilenode | relpages
+-------------+----------
+ 16806 | 60
+(1 row)
+</programlisting>
+ </para>
+
+ <para>
+ Each page is typically 8 kilobytes. <literal>relpages</> is only
+ updated by <command>VACUUM</> and <command>ANALYZE</>. To show the
+ space used by <acronym>TOAST</> tables, use a query based on the heap
+ relfilenode:
+<programlisting>
+play=# SELECT relname, relpages
+play-# FROM pg_class
+play-# WHERE relname = 'pg_toast_16806' or
+play-# relname = 'pg_toast_16806_index'
+play-# ORDER BY relname;
+ relname | relpages
+----------------------+----------
+ pg_toast_16806 | 0
+ pg_toast_16806_index | 1
+</programlisting>
+ </para>
+
+ <para>
+ You can easily display index usage too:
+<programlisting>
+play=# SELECT c2.relname, c2.relpages
+play-# FROM pg_class c, pg_class c2, pg_index i
+play-# WHERE c.relname = 'customer' AND
+play-# c.oid = i.indrelid AND
+play-# c2.oid = i.indexrelid
+play-# ORDER BY c2.relname;
+ relname | relpages
+----------------------+----------
+ customer_id_indexdex | 26
+</programlisting>
+ </para>
+
+ <para>
+ It is easy to find your largest files using <application>psql</>:
+<programlisting>
+play=# SELECT relname, relpages
+play-# FROM pg_class
+play-# ORDER BY relpages DESC;
+ relname | relpages
+----------------------+----------
+ bigtable | 3290
+ customer | 3144
+</programlisting>
+ </para>
+
+ <para>
+ You can also use <application>oid2name</> to show disk usage. See
+ <filename>README.oid2name</> for examples. It includes a script
+ shows disk usage for each database.
+ </para>
+ </sect1>
+
+
<sect1 id="logfile-maintenance">
<title>Log File Maintenance</title>