<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >pg_lsn Type</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 9.6.21 Documentation" HREF="index.html"><LINK REL="UP" TITLE="Data Types" HREF="datatype.html"><LINK REL="PREVIOUS" TITLE="Object Identifier Types" HREF="datatype-oid.html"><LINK REL="NEXT" TITLE="Pseudo-Types" HREF="datatype-pseudo.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="2021-02-27T18:26:08"></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 9.6.21 Documentation</A ></TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A TITLE="Object Identifier Types" HREF="datatype-oid.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="datatype.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Chapter 8. Data Types</TD ><TD WIDTH="20%" ALIGN="right" VALIGN="top" ><A TITLE="Pseudo-Types" HREF="datatype-pseudo.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="DATATYPE-PG-LSN" >8.19. <ACRONYM CLASS="ACRONYM" >pg_lsn Type</ACRONYM ></A ></H1 ><P > The <TT CLASS="TYPE" >pg_lsn</TT > data type can be used to store LSN (Log Sequence Number) data which is a pointer to a location in the XLOG. This type is a representation of <TT CLASS="TYPE" >XLogRecPtr</TT > and an internal system type of <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN >. </P ><P > Internally, an LSN is a 64-bit integer, representing a byte position in the write-ahead log stream. It is printed as two hexadecimal numbers of up to 8 digits each, separated by a slash; for example, <TT CLASS="LITERAL" >16/B374D848</TT >. The <TT CLASS="TYPE" >pg_lsn</TT > type supports the standard comparison operators, like <TT CLASS="LITERAL" >=</TT > and <TT CLASS="LITERAL" >></TT >. Two LSNs can be subtracted using the <TT CLASS="LITERAL" >-</TT > operator; the result is the number of bytes separating those write-ahead log positions. </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="datatype-oid.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="datatype-pseudo.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Object Identifier Types</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="datatype.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Pseudo-Types</TD ></TR ></TABLE ></DIV ></BODY ></HTML >