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218 lines
16 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head>
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<meta content="text/html; charset=UTF-8" http-equiv="Content-Type" />
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<!--
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XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
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This file is generated from xml source: DO NOT EDIT
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XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
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-->
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<title>prefork - Apache HTTP Server Version 2.5</title>
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<link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
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<link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" />
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<script src="../style/scripts/prettify.min.js" type="text/javascript">
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</script>
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<link href="../images/favicon.ico" rel="shortcut icon" /></head>
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<body>
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<div id="page-header">
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<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/quickreference.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
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<p class="apache">Apache HTTP Server Version 2.5</p>
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<img alt="" src="../images/feather.png" /></div>
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<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
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<div id="path">
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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> > <a href="./">Modules</a></div>
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<div id="page-content">
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<div id="preamble"><h1>Apache MPM prefork</h1>
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<div class="toplang">
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<p><span>Available Languages: </span><a href="../de/mod/prefork.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> |
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<a href="../en/mod/prefork.html" title="English"> en </a> |
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<a href="../fr/mod/prefork.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
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<a href="../ja/mod/prefork.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
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<a href="../tr/mod/prefork.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a></p>
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</div>
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<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Implements a non-threaded, pre-forking web server</td></tr>
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<tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr>
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<tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>mpm_prefork_module</td></tr>
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<tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>prefork.c</td></tr></table>
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<h3>Summary</h3>
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<p>This Multi-Processing Module (MPM) implements a non-threaded,
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pre-forking web server. Each server process may answer incoming
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requests, and a parent process manages the size of the server pool.
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It is appropriate for sites that need to avoid
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threading for compatibility with non-thread-safe libraries. It
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is also the best MPM for isolating each request, so that a problem
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with a single request will not affect any other.</p>
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<p>This MPM is very self-regulating, so it is rarely necessary to
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adjust its configuration directives. Most important is that
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<code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> be big enough
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to handle as many simultaneous requests as you expect to receive, but
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small enough to assure that there is enough physical RAM for all
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processes.</p>
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</div>
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<div id="quickview"><h3>Topics</h3>
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<ul id="topics">
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<li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
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</ul><h3 class="directives">Directives</h3>
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<ul id="toc">
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#enableexceptionhook">EnableExceptionHook</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#group">Group</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#maxspareservers">MaxSpareServers</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#minspareservers">MinSpareServers</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#receivebuffersize">ReceiveBufferSize</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#user">User</a></li>
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</ul>
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<h3>Bugfix checklist</h3><ul class="seealso"><li><a href="https://www.apache.org/dist/httpd/CHANGES_2.4">httpd changelog</a></li><li><a href="https://bz.apache.org/bugzilla/buglist.cgi?bug_status=__open__&list_id=144532&product=Apache%20httpd-2&query_format=specific&order=changeddate%20DESC%2Cpriority%2Cbug_severity&component=mpm_prefork">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2&component=mpm_prefork">Report a bug</a></li></ul><h3>See also</h3>
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<ul class="seealso">
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<li><a href="../bind.html">Setting which addresses and ports Apache HTTP Server
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uses</a></li>
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<li><a href="#comments_section">Comments</a></li></ul></div>
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="section">
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<h2><a name="how-it-works" id="how-it-works">How it Works</a> <a title="Permanent link" href="#how-it-works" class="permalink">¶</a></h2>
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<p>A single control process is responsible for launching child
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processes which listen for connections and serve them when they
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arrive. Apache httpd always tries to maintain several <dfn>spare</dfn>
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or idle server processes, which stand ready to serve incoming
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requests. In this way, clients do not need to wait for a new
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child processes to be forked before their requests can be
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served.</p>
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<p>The <code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code>,
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<code class="directive"><a href="#minspareservers">MinSpareServers</a></code>,
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<code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code>, and
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<code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> regulate how
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the parent process creates children to serve requests. In general,
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Apache httpd is very self-regulating, so most sites do not need to
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adjust these directives from their default values. Sites which
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need to serve more than 256 simultaneous requests may need to
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increase <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>,
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while sites with limited memory may need to decrease <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> to keep the server from
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thrashing (swapping memory to disk and back). More information
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about tuning process creation is provided in the <a href="../misc/perf-tuning.html">performance hints</a>
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documentation.</p>
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<p>While the parent process is usually started as <code>root</code>
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under Unix in order to bind to port 80, the child processes are
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launched by Apache httpd as a less-privileged user. The <code class="directive"><a href="../mod/mod_unixd.html#user">User</a></code> and <code class="directive"><a href="../mod/mod_unixd.html#group">Group</a></code> directives are used to set
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the privileges of the Apache httpd child processes. The child processes
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must be able to read all the content that will be served, but
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should have as few privileges beyond that as possible.</p>
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<p><code class="directive"><a href="../mod/mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</a></code>
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controls how frequently the server recycles processes by killing
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old ones and launching new ones.</p>
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<p>This MPM uses the <code>mpm-accept</code> mutex to serialize
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access to incoming connections when subject to the thundering herd
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problem (generally, when there are multiple listening sockets).
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The implementation aspects of this mutex can be configured with the
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<code class="directive"><a href="../mod/core.html#mutex">Mutex</a></code> directive. The <a href="../misc/perf-tuning.html">performance hints</a>
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documentation has additional information about this mutex.</p>
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</div>
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="directive-section"><h2><a name="MaxSpareServers" id="MaxSpareServers">MaxSpareServers</a> <a name="maxspareservers" id="maxspareservers">Directive</a> <a title="Permanent link" href="#maxspareservers" class="permalink">¶</a></h2>
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<table class="directive">
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<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Maximum number of idle child server processes</td></tr>
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<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MaxSpareServers <var>number</var></code></td></tr>
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<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MaxSpareServers 10</code></td></tr>
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<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
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<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
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<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>prefork</td></tr>
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</table>
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<p>The <code class="directive">MaxSpareServers</code> directive sets the
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desired maximum number of <em>idle</em> child server processes. An
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idle process is one which is not handling a request. If there are
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more than <code class="directive">MaxSpareServers</code> idle, then the
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parent process will kill off the excess processes.</p>
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<p>Tuning of this parameter should only be necessary on very
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busy sites. Setting this parameter to a large number is almost
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always a bad idea. If you are trying to set the value equal to or lower than
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<code class="directive"><a href="#minspareservers">MinSpareServers</a></code>, Apache HTTP Server
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will automatically adjust it to <code class="directive">MinSpareServers</code><code> + 1</code>.</p>
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<h3>See also</h3>
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<ul>
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<li><code class="directive"><a href="#minspareservers">MinSpareServers</a></code></li>
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<li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li>
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<li><code class="directive"><a href="../mod/mpm_common.html#maxsparethreads">MaxSpareThreads</a></code></li>
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</ul>
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</div>
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="directive-section"><h2><a name="MinSpareServers" id="MinSpareServers">MinSpareServers</a> <a name="minspareservers" id="minspareservers">Directive</a> <a title="Permanent link" href="#minspareservers" class="permalink">¶</a></h2>
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<table class="directive">
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<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Minimum number of idle child server processes</td></tr>
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<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MinSpareServers <var>number</var></code></td></tr>
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<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>MinSpareServers 5</code></td></tr>
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<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
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<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
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<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>prefork</td></tr>
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</table>
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<p>The <code class="directive">MinSpareServers</code> directive sets the
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desired minimum number of <em>idle</em> child server processes. An
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idle process is one which is not handling a request. If there are
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fewer than <code class="directive">MinSpareServers</code> idle, then the parent
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process creates new children: It will spawn one, wait a second, then spawn
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two, wait a second, then spawn four, and it will
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continue exponentially until it is spawning 32 children per second. It will
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stop whenever it satisfies the <code class="directive">MinSpareServers</code>
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setting.</p>
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<p>Tuning of this parameter should only be necessary on very
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busy sites. Setting this parameter to a large number is almost
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always a bad idea.</p>
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<h3>See also</h3>
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<ul>
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<li><code class="directive"><a href="#maxspareservers">MaxSpareServers</a></code></li>
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<li><code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code></li>
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<li><code class="directive"><a href="../mod/mpm_common.html#minsparethreads">MinSpareThreads</a></code></li>
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</ul>
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</div>
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</div>
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<div class="bottomlang">
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<p><span>Available Languages: </span><a href="../de/mod/prefork.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> |
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<a href="../en/mod/prefork.html" title="English"> en </a> |
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<a href="../fr/mod/prefork.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
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<a href="../ja/mod/prefork.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
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<a href="../tr/mod/prefork.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a></p>
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</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 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 Libera.chat, or sent to our <a href="https://httpd.apache.org/lists.html">mailing lists</a>.</div>
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