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231 lines
8.7 KiB
HTML
231 lines
8.7 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta name="generator" content="HTML Tidy, see www.w3.org" />
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<title>Apache MPM prefork</title>
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</head>
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<!-- Background white, links blue (unvisited), navy (visited), red (active) -->
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<body bgcolor="#FFFFFF" text="#000000" link="#0000FF"
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vlink="#000080" alink="#FF0000">
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<!--#include virtual="header.html" -->
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<h1 align="CENTER">Multi-Processing Module prefork</h1>
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<p>This Multi-Processing Module implements a non-threaded,
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pre-forking web server.</p>
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<p><a href="module-dict.html#Status"
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rel="Help"><strong>Status:</strong></a> MPM<br />
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<a href="module-dict.html#SourceFile"
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rel="Help"><strong>Source File:</strong></a> prefork.c<br />
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<a href="module-dict.html#ModuleIdentifier"
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rel="Help"><strong>Module Identifier:</strong></a>
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mpm_prefork_module</p>
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<h2>Summary</h2>
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<p>This Multi-Processing Module (MPM) implements a
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non-threaded, pre-forking web server which handles request in a
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manner very similar to the default behavior of Apache 1.3 on
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Unix.</p>
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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 always tries to maintain several <em>spare</em>
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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>StartServers</code>, <code>MinSpareServers</code>,
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<code>MaxSpareServers</code>, and <code>MaxClients</code>
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regulate how the parent process creates children to serve
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requests. In general, Apache is very self-regulating, so most
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sites do not need to adjust these directives from their default
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values. Sites which need to serve more than 256 simultaneous
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requests may need to increase <code>MaxClients</code>, while
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sites with limited memory may need to decrease
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<code>MaxClients</code> to keep the server from thrashing
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(swapping memory to disk and back). More information about
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tuning process creation is provided in the <a
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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 root under
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Unix in order to bind to port 80, the child processes are
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launched by Apache as a less-privileged user. The
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<code>User</code> and <code>Group</code> directives are used to
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set the privileges of the Apache child processes. The child
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processes must be able to read all the content that will be
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served, but should have as few privileges beyond that as
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possible. In addition, unless <a
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href="../suexec.html">suexec</a> is used, these directives also
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set the privileges which will be inherited by CGI scripts.</p>
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<p><code>MaxRequestsPerChild</code> controls how frequently the
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server recycles processes by killing old ones and launching new
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ones.</p>
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<p>See also: <a href="../bind.html">Setting which addresses and
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ports Apache uses</a>.</p>
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<h2>Directives</h2>
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<ul>
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<li><a href="#acceptmutex">AcceptMutex</a></li>
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<li><a
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href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li>
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<li><a href="mpm_common.html#group">Group</a></li>
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<li><a href="mpm_common.html#pidfile">PidFile</a></li>
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<li><a href="mpm_common.html#listen">Listen</a></li>
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<li><a
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href="mpm_common.html#listenbacklog">ListenBacklog</a></li>
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<li><a href="mpm_common.html#lockfile">LockFile</a></li>
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<li><a href="mpm_common.html#maxclients">MaxClients</a></li>
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<li><a
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href="mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</a></li>
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<li><a href="#maxspareservers">MaxSpareServers</a></li>
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<li><a href="#minspareservers">MinSpareServers</a></li>
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<li><a
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href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li>
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<li><a
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href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
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<li><a
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href="mpm_common.html#startservers">StartServers</a></li>
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<li><a href="mpm_common.html#user">User</a></li>
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</ul>
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<hr />
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<h2><a id="AcceptMutex" name="AcceptMutex">AcceptMutex
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Directive</a></h2>
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<p><a href="directive-dict.html#Syntax"
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rel="Help"><strong>Syntax:</strong></a> AcceptMutex
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default|<em>method</em><br />
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<a href="directive-dict.html#Default"
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rel="Help"><strong>Default:</strong></a> <code>AcceptMutex
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default</code><br />
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<a href="directive-dict.html#Context"
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rel="Help"><strong>Context:</strong></a> server config<br />
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<a href="directive-dict.html#Status"
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rel="Help"><strong>Status:</strong></a> core</p>
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<p>The <code>AcceptMutex</code> directives sets the method that
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Apache uses to serialize multiple children accepting requests
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on network sockets. Prior to Apache 2.0, the method was
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selectable only at compile time. The optimal method to use is
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highly architecture and platform dependent. For further
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details, see the <a href="../misc/perf-tuning.html">performance
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tuning</a> documentation.</p>
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<p>If this directive is set to <code>default</code>, then the
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compile-time selected default will be used. Other possible
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methods are listed below. Note that not all methods are
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available on all platforms. If a method is specified which is
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not available, a message will be written to the error log
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listing the available methods.</p>
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<dl>
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<dt><code>flock</code></dt>
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<dd>uses the <code>flock(2)</code> system call to lock the
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file defined by the <a
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href="mpm_common.html#lockfile">LockFile</a> directive.</dd>
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<dt><code>fcntl</code></dt>
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<dd>uses the <code>fnctl(2)</code> system call to lock the
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file defined by the <a
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href="mpm_common.html#lockfile">LockFile</a> directive.</dd>
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<dt><code>sysvsem</code></dt>
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<dd>uses SySV-style semaphores to implement the mutex.</dd>
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<dt><code>proc_pthread</code></dt>
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<dd>uses POSIX mutexes as implemented by the POSIX Threads
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(PThreads) specification.</dd>
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</dl>
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<hr />
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<h2><a id="maxspareservers"
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name="maxspareservers">MaxSpareServers directive</a></h2>
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<!--%plaintext <?INDEX {\tt MaxSpareServers} directive> -->
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<a href="directive-dict.html#Syntax"
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rel="Help"><strong>Syntax:</strong></a> MaxSpareServers
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<em>number</em><br />
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<a href="directive-dict.html#Default"
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rel="Help"><strong>Default:</strong></a> <code>MaxSpareServers
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10</code><br />
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<a href="directive-dict.html#Context"
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rel="Help"><strong>Context:</strong></a> server config<br />
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<a href="directive-dict.html#Status"
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rel="Help"><strong>Status:</strong></a> core
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<p>The MaxSpareServers directive sets the desired maximum
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number of <em>idle</em> child server processes. An idle process
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is one which is not handling a request. If there are more than
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MaxSpareServers idle, then the parent process will kill off the
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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.</p>
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<p>See also <a href="#minspareservers">MinSpareServers</a> and
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<a href="mpm_common.html#startservers">StartServers</a>.</p>
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<hr />
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<h2><a id="minspareservers"
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name="minspareservers">MinSpareServers directive</a></h2>
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<!--%plaintext <?INDEX {\tt MinSpareServers} directive> -->
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<a href="directive-dict.html#Syntax"
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rel="Help"><strong>Syntax:</strong></a> MinSpareServers
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<em>number</em><br />
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<a href="directive-dict.html#Default"
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rel="Help"><strong>Default:</strong></a> <code>MinSpareServers
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5</code><br />
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<a href="directive-dict.html#Context"
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rel="Help"><strong>Context:</strong></a> server config<br />
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<a href="directive-dict.html#Status"
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rel="Help"><strong>Status:</strong></a> core
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<p>The MinSpareServers directive sets the desired minimum
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number of <em>idle</em> child server processes. An idle process
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is one which is not handling a request. If there are fewer than
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MinSpareServers idle, then the parent process creates new
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children at a maximum rate of 1 per second.</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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<p>This directive has no effect on Microsoft Windows.</p>
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<p>See also <a href="#maxspareservers">MaxSpareServers</a> and
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<a href="mpm_common.html#startservers">StartServers</a>.
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<!--#include virtual="footer.html" -->
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</p>
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</body>
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</html>
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