<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Routine Reindexing</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 8.4.8 Documentation" HREF="index.html"><LINK REL="UP" TITLE="Routine Database Maintenance Tasks" HREF="maintenance.html"><LINK REL="PREVIOUS" TITLE="Routine Vacuuming" HREF="routine-vacuuming.html"><LINK REL="NEXT" TITLE="Log File Maintenance" HREF="logfile-maintenance.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="2011-04-15T03:27:09"></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" >PostgreSQL 8.4.8 Documentation</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="routine-vacuuming.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="maintenance.html" >Fast Backward</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Chapter 23. Routine Database Maintenance Tasks</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="maintenance.html" >Fast Forward</A ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="logfile-maintenance.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="ROUTINE-REINDEX" >23.2. Routine Reindexing</A ></H1 ><A NAME="AEN30447" ></A ><P > In some situations it is worthwhile to rebuild indexes periodically with the <A HREF="sql-reindex.html" ><I >REINDEX</I ></A > command. </P ><P > In <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > releases before 7.4, periodic reindexing was frequently necessary to avoid <SPAN CLASS="QUOTE" >"index bloat"</SPAN >, due to lack of internal space reclamation in B-tree indexes. Any situation in which the range of index keys changed over time — for example, an index on timestamps in a table where old entries are eventually deleted — would result in bloat, because index pages for no-longer-needed portions of the key range were not reclaimed for re-use. Over time, the index size could become indefinitely much larger than the amount of useful data in it. </P ><P > In <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > 7.4 and later, index pages that have become completely empty are reclaimed for re-use. There is still a possibility for inefficient use of space: if all but a few index keys on a page have been deleted, the page remains allocated. So a usage pattern in which all but a few keys in each range are eventually deleted will see poor use of space. For such usage patterns, periodic reindexing is recommended. </P ><P > The potential for bloat in non-B-tree indexes has not been well characterized. It is a good idea to keep an eye on the index's physical size when using any non-B-tree index type. </P ><P > Also, for B-tree indexes a freshly-constructed index is somewhat faster to access than one that has been updated many times, because logically adjacent pages are usually also physically adjacent in a newly built index. (This consideration does not currently apply to non-B-tree indexes.) It might be worthwhile to reindex periodically just to improve access speed. </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="routine-vacuuming.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="logfile-maintenance.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Routine Vacuuming</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="maintenance.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Log File Maintenance</TD ></TR ></TABLE ></DIV ></BODY ></HTML >