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--><title>worker - Apache HTTP Server</title><link href="/style/manual.css" type="text/css" rel="stylesheet"/></head><body><blockquote><div align="center"><img src="/images/sub.gif" alt="[APACHE DOCUMENTATION]"/><h3>Apache HTTP Server Version 2.0</h3></div><h1 align="center">Apache Module worker</h1><table cellspacing="1" cellpadding="0" bgcolor="#cccccc"><tr><td><table bgcolor="#ffffff"><tr><td nowrap="nowrap" valign="top"><span class="help">Description:
</span></td><td>Multi-Processing Module implementing a hybrid
multi-threaded multi-process web server</td></tr><tr><td nowrap="nowrap"><a href="module-dict.html#Status" class="help">Status:
</a></td><td>MPM</td></tr><tr><td nowrap="nowrap"><a href="module-dict.html#ModuleIdentifier" class="help">Module Identifier:
</a></td><td>mpm_worker_module</td></tr></table></td></tr></table><h2>Summary</h2>
<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
<a href="/mod/mpm_common.html#threadsperchild" class="directive"><code class="directive">ThreadsPerChild</code></a> and
<a href="/mod/mpm_common.html#maxclients" class="directive"><code class="directive">MaxClients</code></a>. By multiplying
together the value of these directives you define the total number
of simultaneous connections that the server can handle.</p>
<h2>Directives</h2><ul><li><a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li><li><a href="mpm_common.html#group">Group</a></li><li><a href="mpm_common.html#listen">Listen</a></li><li><a href="mpm_common.html#listenbacklog">ListenBacklog</a></li><li><a href="mpm_common.html#lockfile">LockFile</a></li><li><a href="mpm_common.html#maxclients">MaxClients</a></li><li><a href="mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</a></li><li><a href="mpm_common.html#maxsparethreads">MaxSpareThreads</a></li><li><a href="mpm_common.html#minsparethreads">MinSpareThreads</a></li><li><a href="mpm_common.html#pidfile">PidFile</a></li><li><a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li><li><a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li><li><a href="mpm_common.html#serverlimit">ServerLimit</a></li><li><a href="mpm_common.html#startservers">StartServers</a></li><li><a href="mpm_common.html#threadlimit">ThreadLimit</a></li><li><a href="mpm_common.html#threadsperchild">ThreadsPerChild</a></li><li><a href="mpm_common.html#user">User</a></li></ul><p><strong>See also </strong></p><ul><li><a href="/bind.html">Setting which addresses and
ports Apache uses</a></li></ul><h2>How it Works</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 <a href="/mod/mpm_common.html#threadsperchild" class="directive"><code class="directive">ThreadsPerChild</code></a> directive. The
individual threads then listen for connections and serve them when
they arrive.</p>
<p>Apache always tries to maintain a pool of <em>spare</em> 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. 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 <a href="/mod/mpm_common.html#minsparethreads" class="directive"><code class="directive">MinSpareThreads</code></a> and <a href="/mod/mpm_common.html#maxsparethreads" class="directive"><code class="directive">MaxSpareThreads</code></a>. 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 is determined by
multiplying the maximum number of server processes that will be
created (<a href="/mod/mpm_common.html#maxclients" class="directive"><code class="directive">MaxClients</code></a>) by
the number of threads created in each process (<a href="/mod/mpm_common.html#threadsperchild" class="directive"><code class="directive">ThreadsPerChild</code></a>).</p>
<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 <a href="/mod/mpm_common.html#user" class="directive"><code class="directive">User</code></a> and <a href="/mod/mpm_common.html#group" class="directive"><code class="directive">Group</code></a> 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
these directives also set the privileges which will be inherited
by CGI scripts.</p>
<p><a href="/mod/mpm_common.html#maxrequestsperchild" class="directive"><code class="directive">MaxRequestsPerChild</code></a>
controls how frequently the server recycles processes by killing
old ones and launching new ones.</p>
