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   8 <title>worker - Apache HTTP Server</title>
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  15 <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>
  16 <p class="apache">Apache HTTP Server Version 2.4</p>
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  20 <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>
  21 <div id="page-content">
  22 <div id="preamble"><h1>Apache MPM worker</h1>
  23 <div class="toplang">
  24 <p><span>Available Languages: </span><a href="../de/mod/worker.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
  25 <a href="../en/mod/worker.html" title="English">&nbsp;en&nbsp;</a> |
  26 <a href="../ja/mod/worker.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
  27 <a href="../tr/mod/worker.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a></p>
  28 </div>
  29 <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Multi-Processing Module implementing a hybrid
  30     multi-threaded multi-process web server</td></tr>
  31 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr>
  32 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>mpm_worker_module</td></tr>
  33 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>worker.c</td></tr></table>
  34 <h3>Summary</h3>
  35
  36     <p>This Multi-Processing Module (MPM) implements a hybrid
  37     multi-process multi-threaded server. By using threads to serve
  38     requests, it is able to serve a large number of requests with
  39     fewer system resources than a process-based server. However, it
  40     retains much of the stability of a process-based server by
  41     keeping multiple processes available, each with many threads.</p>
  42
  43     <p>The most important directives used to control this MPM are
  44     <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code>, which
  45     controls the number of threads deployed by each child process and
  46     <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>, which
  47     controls the maximum total number of threads that may be
  48     launched.</p>
  49 </div>
  50 <div id="quickview"><h3 class="directives">Directives</h3>
  51 <ul id="toc">
  52 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li>
  53 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#enableexceptionhook">EnableExceptionHook</a></li>
  54 <li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#group">Group</a></li>
  55 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li>
  56 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li>
  57 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</a></li>
  58 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li>
  59 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></li>
  60 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxsparethreads">MaxSpareThreads</a></li>
  61 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#minsparethreads">MinSpareThreads</a></li>
  62 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li>
  63 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#receivebuffersize">ReceiveBufferSize</a></li>
  64 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li>
  65 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
  66 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li>
  67 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li>
  68 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadlimit">ThreadLimit</a></li>
  69 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadsperchild">ThreadsPerChild</a></li>
  70 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadstacksize">ThreadStackSize</a></li>
  71 <li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#user">User</a></li>
  72 </ul>
  73 <h3>Topics</h3>
  74 <ul id="topics">
  75 <li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
  76 </ul><h3>See also</h3>
  77 <ul class="seealso">
  78 <li><a href="../bind.html">Setting which addresses and ports Apache HTTP Server uses</a></li>
  79 </ul></div>
  80 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
  81 <div class="section">
  82 <h2><a name="how-it-works" id="how-it-works">How it Works</a></h2>
  83     <p>A single control process (the parent) is responsible for launching
  84     child processes. Each child process creates a fixed number of server
  85     threads as specified in the <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> directive, as well
  86     as a listener thread which listens for connections and passes them
  87     to a server thread for processing when they arrive.</p>
  88
  89     <p>Apache HTTP Server always tries to maintain a pool of <dfn>spare</dfn> or
  90     idle server threads, which stand ready to serve incoming
  91     requests. In this way, clients do not need to wait for a new
  92     threads or processes to be created before their requests can be
  93     served. The number of processes that will initially launched is
  94     set by the <code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code>
  95     directive. During operation, the server assesses the total number
  96     of idle threads in all processes, and forks or kills processes to
  97     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
  98     process is very self-regulating, it is rarely necessary to modify
  99     these directives from their default values. The maximum number of
 100     clients that may be served simultaneously (i.e., the maximum total
 101     number of threads in all processes) is determined by the
 102     <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> directive.
 103     The maximum number of active child processes is determined by
 104     the <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>
 105     directive divided by the <code class="directive"><a href="../mod/mpm_common.html#&#10;    threadsperchild">
 106     ThreadsPerChild</a></code> directive.</p>
 107
 108     <p>Two directives set hard limits on the number of active child
 109     processes and the number of server threads in a child process,
 110     and can only be changed by fully stopping the server and then
 111     starting it again.  <code class="directive"><a href="../mod/mpm_common.html#serverlimit&#10;    ">ServerLimit
 112     </a></code> is a hard limit on the number of active child
 113     processes, and must be greater than or equal to the
 114     <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>
 115     directive divided by the <code class="directive"><a href="../mod/mpm_common.html#&#10;    threadsperchild">
 116     ThreadsPerChild</a></code> directive.
 117     <code class="directive"><a href="../mod/mpm_common.html#threadlimit">ThreadLimit</a></code> is a hard
 118     limit of the number of server threads, and must be greater than
 119     or equal to the <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> directive.</p>
 120
 121     <p>In addition to the set of active child processes, there may
 122     be additional child processes which are terminating, but where at
 123     least one server thread is still handling an existing client
 124     connection.  Up to <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> terminating processes
 125     may be present, though the actual number can be expected to be
 126     much smaller.  This behavior can be avoided by disabling the
 127     termination of individual child processes, which is achieved using
 128     the following:</p>
 129
 130     <ul>
 131       <li>set the value of <code class="directive"><a href="../mod/mpm_common.html#&#10;      maxconnectionsperchild">
 132       MaxConnectionsPerChild</a></code> to zero</li>
 133
 134       <li>set the value of <code class="directive"><a href="../mod/mpm_common.html#&#10;      maxsparethreads">
 135       MaxSpareThreads</a></code> to the same value as
 136       <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code></li>
 137     </ul>
 138
 139     <p>A typical configuration of the process-thread controls in
 140     the <code class="module"><a href="../mod/worker.html">worker</a></code> MPM could look as follows:</p>
 141
 142     <div class="example"><p><code>
 143       ServerLimit         16<br />
 144       StartServers         2<br />
 145       MaxRequestWorkers         150<br />
 146       MinSpareThreads     25<br />
 147       MaxSpareThreads     75<br />
 148       ThreadsPerChild     25
 149     </code></p></div>
 150
 151     <p>While the parent process is usually started as <code>root</code>
 152     under Unix in order to bind to port 80, the child processes and threads
 153     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
 154     the privileges of the Apache HTTP Server child processes. The child processes
 155     must be able to read all the content that will be served, but
 156     should have as few privileges beyond that as possible. In
 157     addition, unless <code class="program"><a href="../programs/suexec.html">suexec</a></code> is used,
 158     these directives also set the privileges which will be inherited
 159     by CGI scripts.</p>
 160
 161     <p><code class="directive"><a href="../mod/mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</a></code>
 162     controls how frequently the server recycles processes by killing
 163     old ones and launching new ones.</p>
 164
 165     <p>This MPM uses the <code>mpm-accept</code> mutex to serialize
 166     access to incoming connections when subject to the thundering herd
 167     problem (generally, when there are multiple listening sockets).
 168     The implementation aspects of this mutex can be configured with the
 169     <code class="directive"><a href="../mod/core.html#mutex">Mutex</a></code> directive.  The <a href="../misc/perf-tuning.html">performance hints</a>
 170     documentation has additional information about this mutex.</p>
 171 </div>
 172 </div>
 173 <div class="bottomlang">
 174 <p><span>Available Languages: </span><a href="../de/mod/worker.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
 175 <a href="../en/mod/worker.html" title="English">&nbsp;en&nbsp;</a> |
 176 <a href="../ja/mod/worker.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
 177 <a href="../tr/mod/worker.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a></p>
 178 </div><div id="footer">
 179 <p class="apache">Copyright 2011 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>
 180 <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></div>
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