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<title>worker - Apache HTTP Server</title>
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<p class="apache">Apache HTTP Server Version 2.1</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-project/">Documentation</a> > <a href="../">Version 2.1</a> > <a href="./">Modules</a></div>
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<div id="preamble"><h1>Apache MPM worker</h1>
<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Multi-Processing Module implementing a hybrid
multi-threaded multi-process web server</td></tr>
<tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr>
<tr><th><a href="module-dict.html#ModuleIdentifier">Module�Identifier:</a></th><td>mpm_worker_module</td></tr>
<tr><th><a href="module-dict.html#SourceFile">Source�File:</a></th><td>worker.c</td></tr></table>
<h3>Summary</h3>
<p>This Multi-Processing Module (MPM) implements a hybrid
multi-process multi-threaded server. By using threads to serve
requests, it is able to serve a large number of requests with
less system resources than a process-based server. Yet it
retains much of the stability of a process-based server by
keeping multiple processes available, each with many threads.</p>
<p>The most important directives used to control this MPM are
<code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code>, which
controls the number of threads deployed by each child process and
<code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code>, which
controls the maximum total number of threads that may be
launched.</p>
</div>
<div id="quickview"><h3 class="directives">Directives</h3>
<ul id="toc">
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#acceptmutex">AcceptMutex</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#group">Group</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#lockfile">LockFile</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxclients">MaxClients</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxsparethreads">MaxSpareThreads</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#minsparethreads">MinSpareThreads</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadlimit">ThreadLimit</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadsperchild">ThreadsPerChild</a></li>
<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#user">User</a></li>
</ul>
<h3>Topics</h3>
<ul id="topics">
<li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
</ul><h3>See also</h3>
<ul class="seealso">
<li><a href="../bind.html">Setting which addresses and ports Apache
uses</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="how-it-works" id="how-it-works">How it Works</a></h2>
<p>Each process has a fixed
number of threads. The server adjusts to handle load by
increasing or decreasing the number of processes.</p>
<p>A single control process is responsible for launching child
processes. Each child process creates a fixed number of threads as
specified in the <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> directive. The
individual threads then listen for connections and serve them when
they arrive.</p>
<p>Apache always tries to maintain a pool of <dfn>spare</dfn> or
idle server threads, which stand ready to serve incoming
requests. In this way, clients do not need to wait for a new
threads or processes to be created before their requests can be
served. The number of processes that will initially launched is
set by the <code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code>
directive. Then during operation, Apache assesses the total number
of idle threads in all processes, and forks or kills processes to
keep this number within the boundaries specified by <code class="directive"><a href="../mod/mpm_common.html#minsparethreads">MinSpareThreads</a></code> and <code class="directive"><a href="../mod/mpm_common.html#maxsparethreads">MaxSpareThreads</a></code>. Since this
process is very self-regulating, it is rarely necessary to modify
these directives from their default values. The maximum number of
clients that may be served simultaneously (i.e., the maximum total
number of threads in all processes) is determined by the
<code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> directive,
while the maximum number of processes that can be launched is set
by the <code class="directive"><a href="../mod/mpm_common.html#serverlimit">ServerLimit</a></code>
directive. <code class="directive"><a href="../mod/mpm_common.html#serverlimit">ServerLimit</a></code>
multiplied by <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> must be greater
than or equal to <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code></p>
<p>A typical configuration of the process-thread controls in
the <code class="module"><a href="../mod/worker.html">worker</a></code> MPM could look as follows:</p>
<div class="example"><p><code>
StartServers 2<br />
MaxClients 150<br />
MinSpareThreads 25<br />
MaxSpareThreads 75<br />
ThreadsPerChild 25<br />
ServerLimit 16
</code></p></div>
<p>While the parent process is usually started as root under Unix
in order to bind to port 80, the child processes and threads are
launched by Apache as a less-privileged user. The <code class="directive"><a href="../mod/mpm_common.html#user">User</a></code> and <code class="directive"><a href="../mod/mpm_common.html#group">Group</a></code> directives are used to set
the privileges of the Apache child processes. The child processes
must be able to read all the content that will be served, but
should have as few privileges beyond that as possible. In
addition, unless <a href="../suexec.html">suexec</a> is used,
these directives also set the privileges which will be inherited
by CGI scripts.</p>
<p><code class="directive"><a href="../mod/mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</a></code>
controls how frequently the server recycles processes by killing
old ones and launching new ones.</p>
</div>
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