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<title>worker - Apache HTTP Server</title>
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<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../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 2.2</p>
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<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
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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 2.2</a> > <a href="./">Modules</a></div>
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<div id="page-content">
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<div id="preamble"><h1>Apache MPM worker</h1>
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<p><span>Available Languages: </span><a href="../de/mod/worker.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> |
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<a href="../en/mod/worker.html" title="English"> en </a> |
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<a href="../ja/mod/worker.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a></p>
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<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Multi-Processing Module implementing a hybrid
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multi-threaded multi-process 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_worker_module</td></tr>
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<tr><th><a href="module-dict.html#SourceFile">Source�File:</a></th><td>worker.c</td></tr></table>
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<p>This Multi-Processing Module (MPM) implements a hybrid
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multi-process multi-threaded server. By using threads to serve
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requests, it is able to serve a large number of requests with
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fewer system resources than a process-based server. However, it
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retains much of the stability of a process-based server by
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keeping multiple processes available, each with many threads.</p>
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<p>The most important directives used to control this MPM are
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<code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code>, which
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controls the number of threads deployed by each child process and
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<code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code>, which
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controls the maximum total number of threads that may be
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<div id="quickview"><h3 class="directives">Directives</h3>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#acceptmutex">AcceptMutex</a></li>
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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="mpm_common.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#lockfile">LockFile</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxclients">MaxClients</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#maxrequestsperchild">MaxRequestsPerChild</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxsparethreads">MaxSpareThreads</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#minsparethreads">MinSpareThreads</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="mpm_common.html#threadlimit">ThreadLimit</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadsperchild">ThreadsPerChild</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadstacksize">ThreadStackSize</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#user">User</a></li>
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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>See also</h3>
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<li><a href="../bind.html">Setting which addresses and ports Apache
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<h2><a name="how-it-works" id="how-it-works">How it Works</a></h2>
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<p>A single control process (the parent) is responsible for launching
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child processes. Each child process creates a fixed number of server
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threads as specified in the <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> directive, as well
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as a listener thread which listens for connections and passes them
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to a server thread for processing when they arrive.</p>
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<p>Apache always tries to maintain a pool of <dfn>spare</dfn> or
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idle server threads, 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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threads or processes to be created before their requests can be
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served. The number of processes that will initially launched is
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set by the <code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code>
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directive. During operation, Apache assesses the total number
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of idle threads in all processes, and forks or kills processes to
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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
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process is very self-regulating, it is rarely necessary to modify
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these directives from their default values. The maximum number of
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clients that may be served simultaneously (i.e., the maximum total
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number of threads in all processes) is determined by the
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<code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> directive.
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The maximum number of active child processes is determined by
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the <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code>
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directive divided by the <code class="directive"><a href="../mod/mpm_common.html# threadsperchild">
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ThreadsPerChild</a></code> directive.</p>
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<p>Two directives set hard limits on the number of active child
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processes and the number of server threads in a child process,
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and can only be changed by fully stopping the server and then
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starting it again. <code class="directive"><a href="../mod/mpm_common.html#serverlimit ">ServerLimit
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</a></code> is a hard limit on the number of active child
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processes, and must be greater than or equal to the
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<code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code>
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directive divided by the <code class="directive"><a href="../mod/mpm_common.html# threadsperchild">
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ThreadsPerChild</a></code> directive.
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<code class="directive"><a href="../mod/mpm_common.html#threadlimit">ThreadLimit</a></code> is a hard
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limit of the number of server threads, and must be greater than
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or equal to the <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> directive. If
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non-default values are specified for these directives, they
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should appear before other <code class="module"><a href="../mod/worker.html">worker</a></code> directives.</p>
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<p>In addition to the set of active child processes, there may
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be additional child processes which are terminating, but where at
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least one server thread is still handling an existing client
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connection. Up to <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> terminating processes
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may be present, though the actual number can be expected to be
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much smaller. This behavior can be avoided by disabling the
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termination of individual child processes, which is achieved using
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<li>set the value of <code class="directive"><a href="../mod/mpm_common.html# maxrequestsperchild">
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MaxRequestsPerChild</a></code> to zero</li>
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<li>set the value of <code class="directive"><a href="../mod/mpm_common.html# maxsparethreads">
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MaxSpareThreads</a></code> to the same value as
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<code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code></li>
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<p>A typical configuration of the process-thread controls in
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the <code class="module"><a href="../mod/worker.html">worker</a></code> MPM could look as follows:</p>
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<div class="example"><p><code>
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MinSpareThreads 25<br />
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MaxSpareThreads 75<br />
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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 and threads
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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
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the privileges of the Apache 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. In
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addition, unless <code class="program"><a href="../programs/suexec.html">suexec</a></code> is used,
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these directives also set the privileges which will be inherited
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<p><code class="directive"><a href="../mod/mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</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><span>Available Languages: </span><a href="../de/mod/worker.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> |
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<a href="../en/mod/worker.html" title="English"> en </a> |
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<a href="../ja/mod/worker.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a></p>
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</div><div id="footer">
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<p class="apache">Copyright 2006 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
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