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+<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.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>
+<p class="apache">Apache HTTP Server Version 2.4</p>
+<img alt="" src="../images/feather.png" /></div>
+<div class="up"><a href="./"><img title="&lt;-" alt="&lt;-" src="../images/left.gif" /></a></div>
+<div id="path">
+<a href="http://www.apache.org/">Apache</a> &gt; <a href="http://httpd.apache.org/">HTTP Server</a> &gt; <a href="http://httpd.apache.org/docs/">Documentation</a> &gt; <a href="../">Version 2.4</a> &gt; <a href="./">Modules</a></div>
+<div id="page-content">
+<div id="preamble"><h1>Apache MPM worker</h1>
+<div class="toplang">
+<p><span>Available Languages: </span><a href="../de/mod/worker.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
+<a href="../en/mod/worker.html" title="English">&nbsp;en&nbsp;</a> |
+<a href="../fr/mod/worker.html" hreflang="fr" rel="alternate" title="Français">&nbsp;fr&nbsp;</a> |
+<a href="../ja/mod/worker.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
+<a href="../tr/mod/worker.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a></p>
+</div>
+<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
+ fewer system resources than a process-based server. However, 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#maxrequestworkers">MaxRequestWorkers</a></code>, which
+ controls the maximum total number of threads that may be
+ launched.</p>
+</div>
+<div id="quickview"><a href="https://www.apache.org/foundation/contributing.html" class="badge"><img src="https://www.apache.org/images/SupportApache-small.png" alt="Support Apache!" /></a><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 class="directives">Directives</h3>
+<ul id="toc">
+<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#enableexceptionhook">EnableExceptionHook</a></li>
+<li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.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#maxconnectionsperchild">MaxConnectionsPerChild</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#maxrequestworkers">MaxRequestWorkers</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#receivebuffersize">ReceiveBufferSize</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#threadstacksize">ThreadStackSize</a></li>
+<li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#user">User</a></li>
+</ul>
+<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__&amp;list_id=144532&amp;product=Apache%20httpd-2&amp;query_format=specific&amp;order=changeddate%20DESC%2Cpriority%2Cbug_severity&amp;component=mpm_worker">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2&amp;component=mpm_worker">Report a bug</a></li></ul><h3>See also</h3>
+<ul class="seealso">
+<li><a href="../bind.html">Setting which addresses and ports Apache HTTP Server uses</a></li>
+<li><a href="#comments_section">Comments</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>A single control process (the parent) is responsible for launching
+ child processes. Each child process creates a fixed number of server
+ threads as specified in the <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> directive, as well
+ as a listener thread which listens for connections and passes them
+ to a server thread for processing when they arrive.</p>
+
+ <p>Apache HTTP Server 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 launch is
+ set by the <code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code>
+ directive. During operation, the server 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#maxrequestworkers">MaxRequestWorkers</a></code> directive.
+ The maximum number of active child processes is determined by
+ the <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>
+ directive divided by the <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">
+ ThreadsPerChild</a></code> directive.</p>
+
+ <p>Two directives set hard limits on the number of active child
+ processes and the number of server threads in a child process,
+ and can only be changed by fully stopping the server and then
+ starting it again. <code class="directive"><a href="../mod/mpm_common.html#serverlimit">ServerLimit
+ </a></code> is a hard limit on the number of active child
+ processes, and must be greater than or equal to the
+ <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>
+ directive divided by the <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">
+ ThreadsPerChild</a></code> directive.
+ <code class="directive"><a href="../mod/mpm_common.html#threadlimit">ThreadLimit</a></code> is a hard
+ limit of the number of server threads, and must be greater than
+ or equal to the <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> directive.</p>
+
+ <p>In addition to the set of active child processes, there may
+ be additional child processes which are terminating, but where at
+ least one server thread is still handling an existing client
+ connection. Up to <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> terminating processes
+ may be present, though the actual number can be expected to be
+ much smaller. This behavior can be avoided by disabling the
+ termination of individual child processes, which is achieved using
+ the following:</p>
+
+ <ul>
+ <li>set the value of <code class="directive"><a href="../mod/mpm_common.html#maxconnectionsperchild">
+ MaxConnectionsPerChild</a></code> to zero</li>
+
+ <li>set the value of <code class="directive"><a href="../mod/mpm_common.html#maxsparethreads">
+ MaxSpareThreads</a></code> to the same value as
+ <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code></li>
+ </ul>
+
+ <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>
+
+ <pre class="prettyprint lang-config">ServerLimit 16
+StartServers 2
+MaxRequestWorkers 150
+MinSpareThreads 25
+MaxSpareThreads 75
+ThreadsPerChild 25</pre>
+
+
+ <p>While the parent process is usually started as <code>root</code>
+ under Unix in order to bind to port 80, the child processes and threads
+ are launched by the server 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
+ the privileges of the Apache HTTP Server 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 <code class="program"><a href="../programs/suexec.html">suexec</a></code> 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#maxconnectionsperchild">MaxConnectionsPerChild</a></code>
+ controls how frequently the server recycles processes by killing
+ old ones and launching new ones.</p>
+
+ <p>This MPM uses the <code>mpm-accept</code> mutex to serialize
+ access to incoming connections when subject to the thundering herd
+ problem (generally, when there are multiple listening sockets).
+ The implementation aspects of this mutex can be configured with the
+ <code class="directive"><a href="../mod/core.html#mutex">Mutex</a></code> directive. The <a href="../misc/perf-tuning.html">performance hints</a>
+ documentation has additional information about this mutex.</p>
+</div>
+</div>
+<div class="bottomlang">
+<p><span>Available Languages: </span><a href="../de/mod/worker.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
+<a href="../en/mod/worker.html" title="English">&nbsp;en&nbsp;</a> |
+<a href="../fr/mod/worker.html" hreflang="fr" rel="alternate" title="Français">&nbsp;fr&nbsp;</a> |
+<a href="../ja/mod/worker.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
+<a href="../tr/mod/worker.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a></p>
+</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&amp;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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