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117 lines
3.4 KiB
Plaintext
117 lines
3.4 KiB
Plaintext
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$Header: /cvsroot/pgsql/doc/src/sgml/diskusage.sgml,v 1.3 2002/06/21 19:17:40 momjian Exp $
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<chapter id="diskusage">
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<title>Monitoring Disk Usage</title>
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<sect1 id="disk-usage">
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<title>Monitoring Disk Usage</Title>
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<indexterm zone="disk-usage">
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<primary>disk usage</primary>
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</indexterm>
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<para>
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Each table has a primary heap disk file where most of the data is
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stored. To store long column values, there is also a
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<acronym>TOAST</> file associated with the table, named based on the
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table's oid (actually pg_class.relfilenode), and an index on the
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<acronym>TOAST</> table. There also may be indexes associated with
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the base table.
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</para>
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<para>
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You can monitor disk space from three places: from
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<application>psql</> using <command>VACUUM</> information, from
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<application>psql</> using <application>contrib/dbsize</>, and from
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the command line using <application>contrib/oid2name</>. Using
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<application>psql</> on a recently vacuumed (or analyzed) database,
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you can issue queries to see the disk usage of any table:
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<programlisting>
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play=# SELECT relfilenode, relpages
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play-# FROM pg_class
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play-# WHERE relname = 'customer';
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relfilenode | relpages
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-------------+----------
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16806 | 60
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(1 row)
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</programlisting>
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</para>
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<para>
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Each page is typically 8 kilobytes. (Remember, <literal>relpages</>
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is only updated by <command>VACUUM</> and <command>ANALYZE</>.) To
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show the space used by <acronym>TOAST</> tables, use a query based on
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the heap relfilenode shown above:
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<programlisting>
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play=# SELECT relname, relpages
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play-# FROM pg_class
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play-# WHERE relname = 'pg_toast_16806' or
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play-# relname = 'pg_toast_16806_index'
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play-# ORDER BY relname;
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relname | relpages
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----------------------+----------
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pg_toast_16806 | 0
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pg_toast_16806_index | 1
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</programlisting>
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</para>
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<para>
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You can easily display index usage too:
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<programlisting>
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play=# SELECT c2.relname, c2.relpages
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play-# FROM pg_class c, pg_class c2, pg_index i
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play-# WHERE c.relname = 'customer' AND
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play-# c.oid = i.indrelid AND
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play-# c2.oid = i.indexrelid
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play-# ORDER BY c2.relname;
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relname | relpages
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----------------------+----------
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customer_id_indexdex | 26
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</programlisting>
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</para>
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<para>
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It is easy to find your largest files using <application>psql</>:
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<programlisting>
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play=# SELECT relname, relpages
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play-# FROM pg_class
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play-# ORDER BY relpages DESC;
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relname | relpages
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----------------------+----------
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bigtable | 3290
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customer | 3144
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</programlisting>
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</para>
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<para>
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<application>dbsize</> loads functions into your database that allow
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you to find the size of a table or database from inside
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<application>psql</> without the need for <command>VACUUM/ANALYZE.</>
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</para>
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<para>
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You can also use <application>oid2name</> to show disk usage. See
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<filename>README.oid2name</> for examples. It includes a script
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shows disk usage for each database.
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</para>
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</sect1>
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</chapter>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode:sgml
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sgml-default-dtd-file:"./reference.ced"
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sgml-local-catalogs:("/usr/lib/sgml/catalog")
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sgml-local-ecat-files:nil
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End:
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-->
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