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- <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>28.1. Determining Disk Usage</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="diskusage.html" title="Chapter 28. Monitoring Disk Usage" /><link rel="next" href="disk-full.html" title="28.2. Disk Full Failure" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">28.1. Determining Disk Usage</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="diskusage.html" title="Chapter 28. Monitoring Disk Usage">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="diskusage.html" title="Chapter 28. Monitoring Disk Usage">Up</a></td><th width="60%" align="center">Chapter 28. Monitoring Disk Usage</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="disk-full.html" title="28.2. Disk Full Failure">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="DISK-USAGE"><div class="titlepage"><div><div><h2 class="title" style="clear: both">28.1. Determining Disk Usage</h2></div></div></div><a id="id-1.6.15.3.2" class="indexterm"></a><p>
- Each table has a primary heap disk file where most of the data is
- stored. If the table has any columns with potentially-wide values,
- there also might be a <acronym class="acronym">TOAST</acronym> file associated with the table,
- which is used to store values too wide to fit comfortably in the main
- table (see <a class="xref" href="storage-toast.html" title="68.2. TOAST">Section 68.2</a>). There will be one valid index
- on the <acronym class="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 — possibly more than one file, if the file would
- exceed one gigabyte. Naming conventions for these files are described
- in <a class="xref" href="storage-file-layout.html" title="68.1. Database File Layout">Section 68.1</a>.
- </p><p>
- You can monitor disk space in three ways:
- using the SQL functions listed in <a class="xref" href="functions-admin.html#FUNCTIONS-ADMIN-DBSIZE" title="Table 9.89. Database Object Size Functions">Table 9.89</a>,
- using the <a class="xref" href="oid2name.html" title="oid2name"><span class="refentrytitle">oid2name</span></a> 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.
- </p><p>
- Using <span class="application">psql</span> on a recently vacuumed or analyzed database,
- you can issue queries to see the disk usage of any table:
- </p><pre class="programlisting">
- SELECT pg_relation_filepath(oid), relpages FROM pg_class WHERE relname = 'customer';
-
- pg_relation_filepath | relpages
- ----------------------+----------
- base/16384/16806 | 60
- (1 row)
- </pre><p>
- Each page is typically 8 kilobytes. (Remember, <code class="structfield">relpages</code>
- is only updated by <code class="command">VACUUM</code>, <code class="command">ANALYZE</code>, and
- a few DDL commands such as <code class="command">CREATE INDEX</code>.) The file path name
- is of interest if you want to examine the table's disk file directly.
- </p><p>
- To show the space used by <acronym class="acronym">TOAST</acronym> tables, use a query
- like the following:
- </p><pre class="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 | 0
- pg_toast_16806_index | 1
- </pre><p>
- </p><p>
- You can easily display index sizes, too:
- </p><pre class="programlisting">
- SELECT c2.relname, c2.relpages
- FROM pg_class c, pg_class c2, pg_index i
- WHERE c.relname = 'customer' AND
- c.oid = i.indrelid AND
- c2.oid = i.indexrelid
- ORDER BY c2.relname;
-
- relname | relpages
- -------------------+----------
- customer_id_index | 26
- </pre><p>
- </p><p>
- It is easy to find your largest tables and indexes using this
- information:
- </p><pre class="programlisting">
- SELECT relname, relpages
- FROM pg_class
- ORDER BY relpages DESC;
-
- relname | relpages
- ----------------------+----------
- bigtable | 3290
- customer | 3144
- </pre><p>
- </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="diskusage.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="diskusage.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="disk-full.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 28. Monitoring Disk Usage </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 28.2. Disk Full Failure</td></tr></table></div></body></html>
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