<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Introduction</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REV="MADE" HREF="mailto:pgsql-docs@postgresql.org"><LINK REL="HOME" TITLE="PostgreSQL 9.6.4 Documentation" HREF="index.html"><LINK REL="UP" TITLE="Large Objects" HREF="largeobjects.html"><LINK REL="PREVIOUS" TITLE="Large Objects" HREF="largeobjects.html"><LINK REL="NEXT" TITLE="Implementation Features" HREF="lo-implementation.html"><LINK REL="STYLESHEET" TYPE="text/css" HREF="stylesheet.css"><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"><META NAME="creation" CONTENT="2017-08-11T02:27:18"></HEAD ><BODY CLASS="SECT1" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="4" ALIGN="center" VALIGN="bottom" ><A HREF="index.html" >PostgreSQL 9.6.4 Documentation</A ></TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A TITLE="Large Objects" HREF="largeobjects.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="largeobjects.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Chapter 33. Large Objects</TD ><TD WIDTH="20%" ALIGN="right" VALIGN="top" ><A TITLE="Implementation Features" HREF="lo-implementation.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="LO-INTRO" >33.1. Introduction</A ></H1 ><P > All large objects are stored in a single system table named <A HREF="catalog-pg-largeobject.html" ><TT CLASS="STRUCTNAME" >pg_largeobject</TT ></A >. Each large object also has an entry in the system table <A HREF="catalog-pg-largeobject-metadata.html" ><TT CLASS="STRUCTNAME" >pg_largeobject_metadata</TT ></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 HREF="storage-toast.html" ><SPAN CLASS="QUOTE" >"<ACRONYM CLASS="ACRONYM" >TOAST</ACRONYM >"</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. </P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="largeobjects.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="lo-implementation.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Large Objects</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="largeobjects.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Implementation Features</TD ></TR ></TABLE ></DIV ></BODY ></HTML >