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- <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>24.2. Routine Reindexing</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="routine-vacuuming.html" title="24.1. Routine Vacuuming" /><link rel="next" href="logfile-maintenance.html" title="24.3. Log File Maintenance" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">24.2. Routine Reindexing</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="routine-vacuuming.html" title="24.1. Routine Vacuuming">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="maintenance.html" title="Chapter 24. Routine Database Maintenance Tasks">Up</a></td><th width="60%" align="center">Chapter 24. Routine Database Maintenance Tasks</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="logfile-maintenance.html" title="24.3. Log File Maintenance">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="ROUTINE-REINDEX"><div class="titlepage"><div><div><h2 class="title" style="clear: both">24.2. Routine Reindexing</h2></div></div></div><a id="id-1.6.11.11.2" class="indexterm"></a><p>
- In some situations it is worthwhile to rebuild indexes periodically
- with the <a class="xref" href="sql-reindex.html" title="REINDEX"><span class="refentrytitle">REINDEX</span></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 class="xref" href="sql-reindex.html" title="REINDEX"><span class="refentrytitle">REINDEX</span></a> can be used safely and easily in all cases.
- This command requires an <code class="literal">ACCESS EXCLUSIVE</code> lock by
- default, hence it is often preferable to execute it with its
- <code class="literal">CONCURRENTLY</code> option, which requires only a
- <code class="literal">SHARE UPDATE EXCLUSIVE</code> lock.
- </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="routine-vacuuming.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="maintenance.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="logfile-maintenance.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">24.1. Routine Vacuuming </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 24.3. Log File Maintenance</td></tr></table></div></body></html>
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