<!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 9.3.9 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="2015-06-13T20:07:22"></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 9.3.9 Documentation</A ></TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A TITLE="Routine Vacuuming" HREF="routine-vacuuming.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="maintenance.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Chapter 23. Routine Database Maintenance Tasks</TD ><TD WIDTH="20%" ALIGN="right" VALIGN="top" ><A TITLE="Log File Maintenance" 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 ><P > In some situations it is worthwhile to rebuild indexes periodically with the <A HREF="sql-reindex.html" >REINDEX</A > command or a series of individual rebuilding steps. </P ><P > B-tree index pages that have become completely empty are reclaimed for re-use. However, there is still a possibility of inefficient use of space: if all but a few index keys on a page have been deleted, the page remains allocated. Therefore, a usage pattern in which most, but not all, 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 researched. It is a good idea to periodically monitor 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 slightly 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 apply to non-B-tree indexes.) It might be worthwhile to reindex periodically just to improve access speed. </P ><P > <A HREF="sql-reindex.html" >REINDEX</A > can be used safely and easily in all cases. But since the command requires an exclusive table lock, it is often preferable to execute an index rebuild with a sequence of creation and replacement steps. Index types that support <A HREF="sql-createindex.html" >CREATE INDEX</A > with the <TT CLASS="LITERAL" >CONCURRENTLY</TT > option can instead be recreated that way. If that is successful and the resulting index is valid, the original index can then be replaced by the newly built one using a combination of <A HREF="sql-alterindex.html" >ALTER INDEX</A > and <A HREF="sql-dropindex.html" >DROP INDEX</A >. When an index is used to enforce uniqueness or other constraints, <A HREF="sql-altertable.html" >ALTER TABLE</A > might be necessary to swap the existing constraint with one enforced by the new index. Review this alternate multi-step rebuild approach carefully before using it as there are limitations on which indexes can be reindexed this way, and errors must be handled. </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 >
