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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>35.1. Introduction</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="largeobjects.html" title="Chapter 35. Large Objects" /><link rel="next" href="lo-implementation.html" title="35.2. Implementation Features" /></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">35.1. Introduction</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="largeobjects.html" title="Chapter 35. Large Objects">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="largeobjects.html" title="Chapter 35. Large Objects">Up</a></td><th width="60%" align="center">Chapter 35. Large Objects</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="lo-implementation.html" title="35.2. Implementation Features">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="LO-INTRO"><div class="titlepage"><div><div><h2 class="title" style="clear: both">35.1. Introduction</h2></div></div></div><a id="id-1.7.4.6.2" class="indexterm"></a><p>
All large objects are stored in a single system table named <a class="link" href="catalog-pg-largeobject.html" title="52.30. pg_largeobject"><code class="structname">pg_largeobject</code></a>.
Each large object also has an entry in the system table <a class="link" href="catalog-pg-largeobject-metadata.html" title="52.31. pg_largeobject_metadata"><code class="structname">pg_largeobject_metadata</code></a>.
Large objects can be created, modified, and deleted using a read/write API
that is similar to standard operations on files.
</p><p>
<span class="productname">PostgreSQL</span> also supports a storage system called
<a class="link" href="storage-toast.html" title="68.2. TOAST"><span class="quote">“<span class="quote"><acronym class="acronym">TOAST</acronym></span>”</span></a>,
which automatically stores values
larger than a single database page into a secondary storage area per table.
This makes the large object facility partially obsolete. One
remaining advantage of the large object facility is that it allows values
up to 4 TB in size, whereas <acronym class="acronym">TOAST</acronym>ed fields can be at
most 1 GB. Also, reading and updating portions of a large object can be
done efficiently, while most operations on a <acronym class="acronym">TOAST</acronym>ed
field will read or write the whole value as a unit.
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