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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >pg_largeobject</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 9.2.24 Documentation" HREF="index.html"><LINK REL="UP" TITLE="System Catalogs" HREF="catalogs.html"><LINK REL="PREVIOUS" TITLE="pg_language" HREF="catalog-pg-language.html"><LINK REL="NEXT" TITLE="pg_largeobject_metadata" HREF="catalog-pg-largeobject-metadata.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="2017-11-06T22:43:11"></HEAD ><BODY CLASS="SECT1" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="5" ALIGN="center" VALIGN="bottom" ><A HREF="index.html" >PostgreSQL 9.2.24 Documentation</A ></TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A TITLE="pg_language" HREF="catalog-pg-language.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="catalogs.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Chapter 45. System Catalogs</TD ><TD WIDTH="20%" ALIGN="right" VALIGN="top" ><A TITLE="pg_largeobject_metadata" HREF="catalog-pg-largeobject-metadata.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="CATALOG-PG-LARGEOBJECT" >45.28. <TT CLASS="STRUCTNAME" >pg_largeobject</TT ></A ></H1 ><P > The catalog <TT CLASS="STRUCTNAME" >pg_largeobject</TT > holds the data making up <SPAN CLASS="QUOTE" >"large objects"</SPAN >. A large object is identified by an OID assigned when it is created. Each large object is broken into segments or <SPAN CLASS="QUOTE" >"pages"</SPAN > small enough to be conveniently stored as rows in <TT CLASS="STRUCTNAME" >pg_largeobject</TT >. The amount of data per page is defined to be <TT CLASS="SYMBOL" >LOBLKSIZE</TT > (which is currently <TT CLASS="LITERAL" >BLCKSZ/4</TT >, or typically 2 kB). </P ><P > Prior to <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > 9.0, there was no permission structure associated with large objects. As a result, <TT CLASS="STRUCTNAME" >pg_largeobject</TT > was publicly readable and could be used to obtain the OIDs (and contents) of all large objects in the system. This is no longer the case; use <A HREF="catalog-pg-largeobject-metadata.html" ><TT CLASS="STRUCTNAME" >pg_largeobject_metadata</TT ></A > to obtain a list of large object OIDs. </P ><DIV CLASS="TABLE" ><A NAME="AEN91409" ></A ><P ><B >Table 45-28. <TT CLASS="STRUCTNAME" >pg_largeobject</TT > Columns</B ></P ><TABLE BORDER="1" CLASS="CALSTABLE" ><COL><COL><COL><COL><THEAD ><TR ><TH >Name</TH ><TH >Type</TH ><TH >References</TH ><TH >Description</TH ></TR ></THEAD ><TBODY ><TR ><TD ><TT CLASS="STRUCTFIELD" >loid</TT ></TD ><TD ><TT CLASS="TYPE" >oid</TT ></TD ><TD ><TT CLASS="LITERAL" ><A HREF="catalog-pg-largeobject-metadata.html" ><TT CLASS="STRUCTNAME" >pg_largeobject_metadata</TT ></A >.oid</TT ></TD ><TD >Identifier of the large object that includes this page</TD ></TR ><TR ><TD ><TT CLASS="STRUCTFIELD" >pageno</TT ></TD ><TD ><TT CLASS="TYPE" >int4</TT ></TD ><TD > </TD ><TD >Page number of this page within its large object (counting from zero)</TD ></TR ><TR ><TD ><TT CLASS="STRUCTFIELD" >data</TT ></TD ><TD ><TT CLASS="TYPE" >bytea</TT ></TD ><TD > </TD ><TD > Actual data stored in the large object. This will never be more than <TT CLASS="SYMBOL" >LOBLKSIZE</TT > bytes and might be less. </TD ></TR ></TBODY ></TABLE ></DIV ><P > Each row of <TT CLASS="STRUCTNAME" >pg_largeobject</TT > holds data for one page of a large object, beginning at byte offset (<TT CLASS="LITERAL" >pageno * LOBLKSIZE</TT >) within the object. The implementation allows sparse storage: pages might be missing, and might be shorter than <TT CLASS="LITERAL" >LOBLKSIZE</TT > bytes even if they are not the last page of the object. Missing regions within a large object read as zeroes. </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="catalog-pg-language.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="catalog-pg-largeobject-metadata.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><TT CLASS="STRUCTNAME" >pg_language</TT ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="catalogs.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><TT CLASS="STRUCTNAME" >pg_largeobject_metadata</TT ></TD ></TR ></TABLE ></DIV ></BODY ></HTML >