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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>29.1. 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 Vsnapshot" /><link rel="prev" href="diskusage.html" title="Chapter 29. Monitoring Disk Usage" /><link rel="next" href="disk-full.html" title="29.2. 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">29.1. Determining Disk Usage</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="diskusage.html" title="Chapter 29. Monitoring Disk Usage">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="diskusage.html" title="Chapter 29. Monitoring Disk Usage">Up</a></td><th width="60%" align="center">Chapter 29. Monitoring Disk Usage</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="disk-full.html" title="29.2. 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">29.1. Determining Disk Usage</h2></div></div></div><a id="id-1.6.16.3.2" 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 9.84. Database Object Size Functions">Table 9.84</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_indexdex | 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>
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