on the <acronym>TOAST</acronym> table, if present. There also might be indexes
    associated with the base table.  Each table and index is stored in a
    separate disk file &mdash; possibly more than one file, if the file would
    exceed one gigabyte.  Naming conventions for these files are described
    in <xref linkend="storage-file-layout"/>.
   </para>

   <para>
    You can monitor disk space in three ways:
    using the SQL functions listed in <xref linkend="functions-admin-dbsize"/>,
    using the <xref linkend="oid2name"/> module, or
    using manual inspection of the system catalogs.
    The SQL functions are the easiest to use and are generally recommended.
    The remainder of this section shows how to do it by inspection of the
    system catalogs.
   </para>

   <para>
    Using <application>psql</application> on a recently vacuumed or analyzed
    database, you can issue queries to see the disk usage of any table:
<programlisting>
SELECT pg_relation_filepath(oid), relpages FROM pg_class WHERE relname = 'customer';

 pg_relation_filepath | relpages
----------------------+----------
 base/16384/16806     |       60
(1 row)
</programlisting>
    Each page is typically 8 kilobytes. (Remember, <structfield>relpages</structfield>
    is only updated by <command>VACUUM</command>, <command>ANALYZE</command>, and
    a few DDL commands such as <command>CREATE INDEX</command>.)  The file path name
    is of interest if you want to examine the table's disk file directly.
   </para>

   <para>
    To show the space used by <acronym>TOAST</acronym> tables, use a query
    like the following:
<programlisting>
SELECT relname, relpages
FROM pg_class,
     (SELECT reltoastrelid
      FROM pg_class
      WHERE relname = 'customer') AS ss
WHERE oid = ss.reltoastrelid OR
      oid = (SELECT indexrelid
             FROM pg_index
             WHERE indrelid = ss.reltoastrelid)
ORDER BY relname;

       relname        | relpages
----------------------+----------
 pg_toast_16806