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| <title>Multi-Processing Modules (MPMs) - Apache HTTP Server Version 2.5</title> |
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| <p class="apache">Apache HTTP Server Version 2.5</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 2.5</a></div><div id="page-content"><div id="preamble"><h1>Multi-Processing Modules (MPMs)</h1> |
| <div class="toplang"> |
| <p><span>Available Languages: </span><a href="./de/mpm.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> | |
| <a href="./en/mpm.html" title="English"> en </a> | |
| <a href="./es/mpm.html" hreflang="es" rel="alternate" title="Español"> es </a> | |
| <a href="./fr/mpm.html" hreflang="fr" rel="alternate" title="Français"> fr </a> | |
| <a href="./ja/mpm.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> | |
| <a href="./ko/mpm.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> | |
| <a href="./tr/mpm.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a> | |
| <a href="./zh-cn/mpm.html" hreflang="zh-cn" rel="alternate" title="Simplified Chinese"> zh-cn </a></p> |
| </div> |
| |
| <p>This document describes what a Multi-Processing Module is and |
| how they are used by the Apache HTTP Server.</p> |
| </div> |
| <div id="quickview"><ul id="toc"><li><img alt="" src="./images/down.gif" /> <a href="#introduction">Introduction</a></li> |
| <li><img alt="" src="./images/down.gif" /> <a href="#defaults">MPM Defaults</a></li> |
| <li><img alt="" src="./images/down.gif" /> <a href="#static">Building an MPM as a static module</a></li> |
| <li><img alt="" src="./images/down.gif" /> <a href="#dynamic">Building an MPM as a DSO module</a></li> |
| </ul><h3>See also</h3><ul class="seealso"><li><a href="#comments_section">Comments</a></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="introduction" id="introduction">Introduction</a></h2> |
| |
| <p>The Apache HTTP Server is designed to be a powerful and |
| flexible web server that can work on a very wide variety of |
| platforms in a range of different environments. Different |
| platforms and different environments often require different |
| features, or may have different ways of implementing the same |
| feature most efficiently. Apache httpd has always accommodated a wide |
| variety of environments through its modular design. This design |
| allows the webmaster to choose which features will be included |
| in the server by selecting which modules to load either at |
| compile-time or at run-time.</p> |
| |
| <p>Apache HTTP Server 2.0 extends this modular design to the most basic |
| functions of a web server. The server ships with a selection of |
| Multi-Processing Modules (MPMs) which are responsible for |
| binding to network ports on the machine, accepting requests, |
| and dispatching children to handle the requests.</p> |
| |
| <p>Extending the modular design to this level of the server |
| allows two important benefits:</p> |
| |
| <ul> |
| <li>Apache httpd can more cleanly and efficiently support a wide |
| variety of operating systems. In particular, the Windows |
| version of the server is now much more efficient, since |
| <code class="module"><a href="./mod/mpm_winnt.html">mpm_winnt</a></code> can use native |
| networking features in place of the POSIX layer used in |
| Apache httpd 1.3. This benefit also extends to other operating |
| systems that implement specialized MPMs.</li> |
| |
| <li>The server can be better customized for the needs of the |
| particular site. For example, sites that need a great deal of |
| scalability can choose to use a threaded MPM like |
| <code class="module"><a href="./mod/worker.html">worker</a></code> or <code class="module"><a href="./mod/event.html">event</a></code>, while sites requiring |
| stability or compatibility with older software can use a |
| <code class="module"><a href="./mod/prefork.html">prefork</a></code>.</li> |
| </ul> |
| |
| <p>At the user level, MPMs appear much like other Apache httpd |
| modules. The main difference is that one and only one MPM must |
| be loaded into the server at any time. The list of available |
| MPMs appears on the <a href="mod/">module index page</a>.</p> |
| |
| </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div> |
| <div class="section"> |
| <h2><a name="defaults" id="defaults">MPM Defaults</a></h2> |
| |
| <p>The following table lists the default MPMs for various operating |
| systems. This will be the MPM selected if you do not make another |
| choice at compile-time.</p> |
| |
| <table class="bordered"><tr><td>Netware</td><td><code class="module"><a href="./mod/mpm_netware.html">mpm_netware</a></code></td></tr> |
| <tr class="odd"><td>OS/2</td><td><code class="module"><a href="./mod/mpmt_os2.html">mpmt_os2</a></code></td></tr> |
| <tr><td>Unix</td><td><code class="module"><a href="./mod/prefork.html">prefork</a></code>, <code class="module"><a href="./mod/worker.html">worker</a></code>, or |
| <code class="module"><a href="./mod/event.html">event</a></code>, depending on platform capabilities</td></tr> |
| <tr class="odd"><td>Windows</td><td><code class="module"><a href="./mod/mpm_winnt.html">mpm_winnt</a></code></td></tr> |
| </table> |
| |
| <div class="note"><p>Here, 'Unix' is used to mean Unix-like operating systems, such as |
| Linux, BSD, Solaris, Mac OS X, etc.</p></div> |
| |
| <p>In the case of Unix, the decision as to which MPM is installed is |
| based on two questions:</p> |
| <p>1. Does the system support threads?</p> |
| <p>2. Does the system support thread-safe polling (Specifically, the |
| kqueue and epoll functions)?</p> |
| |
| <p>If the answer to both questions is 'yes', the default MPM is |
| <code class="module"><a href="./mod/event.html">event</a></code>.</p> |
| |
| <p>If The answer to #1 is 'yes', but the answer to #2 is 'no', the |
| default will be <code class="module"><a href="./mod/worker.html">worker</a></code>.</p> |
| |
| <p>If the answer to both questions is 'no', then the default MPM will be |
| <code class="module"><a href="./mod/prefork.html">prefork</a></code>.</p> |
| |
| <p>In practical terms, this means that the default will almost always be |
| <code class="module"><a href="./mod/event.html">event</a></code>, as all modern operating systems support these |
| two features.</p> |
| |
| </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div> |
| <div class="section"> |
| <h2><a name="static" id="static">Building an MPM as a static module</a></h2> |
| |
| <p>MPMs can be built as static modules on all platforms. A single MPM |
| is chosen at build time and linked into the server. The server must |
| be rebuilt in order to change the MPM.</p> |
| |
| <p>To override the default MPM choice, use the |
| <code>--with-mpm=<em>NAME</em></code> option of the |
| <code class="program"><a href="./programs/configure.html">configure</a></code> script. <em>NAME</em> is the name of the |
| desired MPM.</p> |
| |
| <p>Once the server has been compiled, it is possible to determine which MPM |
| was chosen by using <code>./httpd -l</code>. This command will list every |
| module that is compiled into the server, including the MPM.</p> |
| |
| </div><div class="top"><a href="#page-header"><img alt="top" src="./images/up.gif" /></a></div> |
| <div class="section"> |
| <h2><a name="dynamic" id="dynamic">Building an MPM as a DSO module</a></h2> |
| |
| <p>On Unix and similar platforms, MPMs can be built as DSO modules and |
| dynamically loaded into the server in the same manner as other DSO |
| modules. Building MPMs as DSO modules allows the MPM to be changed by |
| updating the <code class="directive"><a href="./mod/mod_so.html#loadmodule">LoadModule</a></code> directive |
| for the MPM instead of by rebuilding the server.</p> |
| |
| <pre class="prettyprint lang-config">LoadModule mpm_prefork_module modules/mod_mpm_prefork.so</pre> |
| |
| |
| <p>Attempting to <code class="directive"><a href="./mod/mod_so.html#loadmodule">LoadModule</a></code> |
| more than one MPM will result in a startup failure with the |
| following error.</p> |
| |
| <div class="example"><p><code>AH00534: httpd: Configuration error: More than one MPM |
| loaded.</code></p></div> |
| |
| <p>This feature is enabled using the |
| <code>--enable-mpms-shared</code> option of the <code class="program"><a href="./programs/configure.html">configure</a></code> |
| script. |
| With argument <code><em>all</em></code>, all possible MPMs for the platform |
| will be installed. Alternately, a list of MPMs can be specified as the |
| argument.</p> |
| |
| <p>The default MPM, either selected automatically or specified with the |
| <code>--with-mpm</code> option of the <code class="program"><a href="./programs/configure.html">configure</a></code> |
| script, will be loaded in the generated server configuration file. Edit the |
| <code class="directive"><a href="./mod/mod_so.html#loadmodule">LoadModule</a></code> directive to select a |
| different MPM.</p> |
| |
| </div></div> |
| <div class="bottomlang"> |
| <p><span>Available Languages: </span><a href="./de/mpm.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> | |
| <a href="./en/mpm.html" title="English"> en </a> | |
| <a href="./es/mpm.html" hreflang="es" rel="alternate" title="Español"> es </a> | |
| <a href="./fr/mpm.html" hreflang="fr" rel="alternate" title="Français"> fr </a> | |
| <a href="./ja/mpm.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> | |
| <a href="./ko/mpm.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> | |
| <a href="./tr/mpm.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a> | |
| <a href="./zh-cn/mpm.html" hreflang="zh-cn" rel="alternate" title="Simplified Chinese"> zh-cn </a></p> |
| </div><div class="top"><a href="#page-header"><img src="./images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our <a href="http://httpd.apache.org/lists.html">mailing lists</a>.</div> |
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