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<title>Apache Performance Tuning - Apache HTTP Server</title>
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<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
<p class="apache">Apache HTTP Server Version 2.0</p>
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<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.0</a> > <a href="./">Miscellaneous Documentation</a></div><div id="page-content"><div id="preamble"><h1>Apache Performance Tuning</h1>
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<p><span>Available Languages: </span><a href="../en/misc/perf-tuning.html" title="English"> en </a> |
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<p>Apache 2.0 is a general-purpose webserver, designed to
provide a balance of flexibility, portability, and performance.
Although it has not been designed specifically to set benchmark
records, Apache 2.0 is capable of high performance in many
real-world situations.</p>
<p>Compared to Apache 1.3, release 2.0 contains many additional
optimizations to increase throughput and scalability. Most of
these improvements are enabled by default. However, there are
compile-time and run-time configuration choices that can
significantly affect performance. This document describes the
options that a server administrator can configure to tune the
performance of an Apache 2.0 installation. Some of these
configuration options enable the httpd to better take advantage
of the capabilities of the hardware and OS, while others allow
the administrator to trade functionality for speed.</p>
</div>
<div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#hardware">Hardware and Operating System Issues</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#runtime">Run-Time Configuration Issues</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#compiletime">Compile-Time Configuration Issues</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#trace">Appendix: Detailed Analysis of a Trace</a></li>
</ul></div>
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<div class="section">
<h2><a name="hardware" id="hardware">Hardware and Operating System Issues</a></h2>
<p>The single biggest hardware issue affecting webserver
performance is RAM. A webserver should never ever have to swap,
as swapping increases the latency of each request beyond a point
that users consider "fast enough". This causes users to hit
stop and reload, further increasing the load. You can, and
should, control the <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> setting so that your server
does not spawn so many children it starts swapping. This procedure
for doing this is simple: determine the size of your average Apache
process, by looking at your process list via a tool such as
<code>top</code>, and divide this into your total available memory,
leaving some room for other processes.</p>
<p>Beyond that the rest is mundane: get a fast enough CPU, a
fast enough network card, and fast enough disks, where "fast
enough" is something that needs to be determined by
experimentation.</p>
<p>Operating system choice is largely a matter of local
concerns. But some guidelines that have proven generally
useful are:</p>
<ul>
<li>
<p>Run the latest stable release and patchlevel of the
operating system that you choose. Many OS suppliers have
introduced significant performance improvements to their
TCP stacks and thread libraries in recent years.</p>
</li>
<li>
<p>If your OS supports a <code>sendfile(2)</code> system
call, make sure you install the release and/or patches
needed to enable it. (With Linux, for example, this means
using Linux 2.4 or later. For early releases of Solaris 8,
you may need to apply a patch.) On systems where it is
available, <code>sendfile</code> enables Apache 2 to deliver
static content faster and with lower CPU utilization.</p>
</li>
</ul>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="runtime" id="runtime">Run-Time Configuration Issues</a></h2>
<table class="related"><tr><th>Related Modules</th><th>Related Directives</th></tr><tr><td><ul><li><code class="module"><a href="../mod/mod_dir.html">mod_dir</a></code></li><li><code class="module"><a href="../mod/mpm_common.html">mpm_common</a></code></li><li><code class="module"><a href="../mod/mod_status.html">mod_status</a></code></li></ul></td><td><ul><li><code class="directive"><a href="../mod/core.html#allowoverride">AllowOverride</a></code></li><li><code class="directive"><a href="../mod/mod_dir.html#directoryindex">DirectoryIndex</a></code></li><li><code class="directive"><a href="../mod/core.html#hostnamelookups">HostnameLookups</a></code></li><li><code class="directive"><a href="../mod/core.html#enablemmap">EnableMMAP</a></code></li><li><code class="directive"><a href="../mod/core.html#enablesendfile">EnableSendfile</a></code></li><li><code class="directive"><a href="../mod/core.html#keepalivetimeout">KeepAliveTimeout</a></code></li><li><code class="directive"><a href="../mod/prefork.html#maxspareservers">MaxSpareServers</a></code></li><li><code class="directive"><a href="../mod/prefork.html#minspareservers">MinSpareServers</a></code></li><li><code class="directive"><a href="../mod/core.html#options">Options</a></code></li><li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li></ul></td></tr></table>
<h3><a name="dns" id="dns">HostnameLookups and other DNS considerations</a></h3>
<p>Prior to Apache 1.3, <code class="directive"><a href="../mod/core.html#hostnamelookups">HostnameLookups</a></code> defaulted to <code>On</code>.
This adds latency to every request because it requires a
DNS lookup to complete before the request is finished. In
Apache 1.3 this setting defaults to <code>Off</code>. If you need
to have addresses in your log files resolved to hostnames, use the
<code class="program"><a href="../programs/logresolve.html">logresolve</a></code>
program that comes with Apache, on one of the numerous log
reporting packages which are available.</p>
<p>It is recommended that you do this sort of postprocessing of
your log files on some machine other than the production web
server machine, in order that this activity not adversely affect
server performance.</p>
<p>If you use any <code><code class="directive"><a href="../mod/mod_access.html#allow">Allow</a></code>
from domain</code> or <code><code class="directive"><a href="../mod/mod_access.html#deny">Deny</a></code> from domain</code>
directives (i.e., using a hostname, or a domain name, rather than
an IP address) then you will pay for
a double reverse DNS lookup (a reverse, followed by a forward
to make sure that the reverse is not being spoofed). For best
performance, therefore, use IP addresses, rather than names, when
using these directives, if possible.</p>
<p>Note that it's possible to scope the directives, such as
within a <code><Location /server-status></code> section.
In this case the DNS lookups are only performed on requests
matching the criteria. Here's an example which disables lookups
except for <code>.html</code> and <code>.cgi</code> files:</p>
<div class="example"><p><code>
HostnameLookups off<br />
<Files ~ "\.(html|cgi)$"><br />
<span class="indent">
HostnameLookups on<br />
</span>
</Files>
</code></p></div>
<p>But even still, if you just need DNS names in some CGIs you
could consider doing the <code>gethostbyname</code> call in the
specific CGIs that need it.</p>
<h3><a name="symlinks" id="symlinks">FollowSymLinks and SymLinksIfOwnerMatch</a></h3>
<p>Wherever in your URL-space you do not have an <code>Options
FollowSymLinks</code>, or you do have an <code>Options
SymLinksIfOwnerMatch</code> Apache will have to issue extra
system calls to check up on symlinks. One extra call per
filename component. For example, if you had:</p>
<div class="example"><p><code>
DocumentRoot /www/htdocs<br />
<Directory /><br />
<span class="indent">
Options SymLinksIfOwnerMatch<br />
</span>
</Directory>
</code></p></div>
<p>and a request is made for the URI <code>/index.html</code>.
Then Apache will perform <code>lstat(2)</code> on
<code>/www</code>, <code>/www/htdocs</code>, and
<code>/www/htdocs/index.html</code>. The results of these
<code>lstats</code> are never cached, so they will occur on
every single request. If you really desire the symlinks
security checking you can do something like this:</p>
<div class="example"><p><code>
DocumentRoot /www/htdocs<br />
<Directory /><br />
<span class="indent">
Options FollowSymLinks<br />
</span>
</Directory><br />
<br />
<Directory /www/htdocs><br />
<span class="indent">
Options -FollowSymLinks +SymLinksIfOwnerMatch<br />
</span>
</Directory>
</code></p></div>
<p>This at least avoids the extra checks for the
<code class="directive"><a href="../mod/core.html#documentroot">DocumentRoot</a></code> path.
Note that you'll need to add similar sections if you
have any <code class="directive"><a href="../mod/mod_alias.html#alias">Alias</a></code> or
<code class="directive"><a href="../mod/mod_rewrite.html#rewriterule">RewriteRule</a></code> paths
outside of your document root. For highest performance,
and no symlink protection, set <code>FollowSymLinks</code>
everywhere, and never set <code>SymLinksIfOwnerMatch</code>.</p>
<h3><a name="htacess" id="htacess">AllowOverride</a></h3>
<p>Wherever in your URL-space you allow overrides (typically
<code>.htaccess</code> files) Apache will attempt to open
<code>.htaccess</code> for each filename component. For
example,</p>
<div class="example"><p><code>
DocumentRoot /www/htdocs<br />
<Directory /><br />
<span class="indent">
AllowOverride all<br />
</span>
</Directory>
</code></p></div>
<p>and a request is made for the URI <code>/index.html</code>.
Then Apache will attempt to open <code>/.htaccess</code>,
<code>/www/.htaccess</code>, and
<code>/www/htdocs/.htaccess</code>. The solutions are similar
to the previous case of <code>Options FollowSymLinks</code>.
For highest performance use <code>AllowOverride None</code>
everywhere in your filesystem.</p>
<h3><a name="negotiation" id="negotiation">Negotiation</a></h3>
<p>If at all possible, avoid content-negotiation if you're
really interested in every last ounce of performance. In
practice the benefits of negotiation outweigh the performance
penalties. There's one case where you can speed up the server.
Instead of using a wildcard such as:</p>
<div class="example"><p><code>
DirectoryIndex index
</code></p></div>
<p>Use a complete list of options:</p>
<div class="example"><p><code>
DirectoryIndex index.cgi index.pl index.shtml index.html
</code></p></div>
<p>where you list the most common choice first.</p>
<p>Also note that explicitly creating a <code>type-map</code>
file provides better performance than using
<code>MultiViews</code>, as the necessary information can be
determined by reading this single file, rather than having to
scan the directory for files.</p>
<p>If your site needs content negotiation consider using
<code>type-map</code> files, rather than the <code>Options
MultiViews</code> directive to accomplish the negotiation. See the
<a href="../content-negotiation.html">Content Negotiation</a>
documentation for a full discussion of the methods of negotiation,
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