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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 2.3</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 2.3</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></p>
  27 </div>
  28 <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Multi-Processing Module implementing a hybrid
  29     multi-threaded multi-process web server</td></tr>
  30 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr>
  31 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>mpm_worker_module</td></tr>
  32 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>worker.c</td></tr></table>
  33 <h3>Summary</h3>
  34
  35     <p>This Multi-Processing Module (MPM) implements a hybrid
  36     multi-process multi-threaded server. By using threads to serve
  37     requests, it is able to serve a large number of requests with
  38     fewer system resources than a process-based server. However, it
  39     retains much of the stability of a process-based server by
  40     keeping multiple processes available, each with many threads.</p>
  41
  42     <p>The most important directives used to control this MPM are
  43     <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code>, which
  44     controls the number of threads deployed by each child process and
  45     <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code>, which
  46     controls the maximum total number of threads that may be
  47     launched.</p>
  48 </div>
  49 <div id="quickview"><h3 class="directives">Directives</h3>
  50 <ul id="toc">
  51 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#acceptmutex">AcceptMutex</a></li>
  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="mpm_common.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#lockfile">LockFile</a></li>
  58 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxclients">MaxClients</a></li>
  59 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li>
  60 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</a></li>
  61 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxsparethreads">MaxSpareThreads</a></li>
  62 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#minsparethreads">MinSpareThreads</a></li>
  63 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li>
  64 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#receivebuffersize">ReceiveBufferSize</a></li>
  65 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li>
  66 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
  67 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li>
  68 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li>
  69 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadlimit">ThreadLimit</a></li>
  70 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadsperchild">ThreadsPerChild</a></li>
  71 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadstacksize">ThreadStackSize</a></li>
  72 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#user">User</a></li>
  73 </ul>
  74 <h3>Topics</h3>
  75 <ul id="topics">
  76 <li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
  77 </ul><h3>See also</h3>
  78 <ul class="seealso">
  79 <li><a href="../bind.html">Setting which addresses and ports Apache
  80 uses</a></li>
  81 </ul></div>
  82 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
  83 <div class="section">
  84 <h2><a name="how-it-works" id="how-it-works">How it Works</a></h2>
  85     <p>A single control process (the parent) is responsible for launching
  86     child processes. Each child process creates a fixed number of server
  87     threads as specified in the <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> directive, as well
  88     as a listener thread which listens for connections and passes them
  89     to a server thread for processing when they arrive.</p>
  90
  91     <p>Apache always tries to maintain a pool of <dfn>spare</dfn> or
  92     idle server threads, which stand ready to serve incoming
  93     requests. In this way, clients do not need to wait for a new
  94     threads or processes to be created before their requests can be
  95     served. The number of processes that will initially launched is
  96     set by the <code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code>
  97     directive. During operation, Apache assesses the total number
  98     of idle threads in all processes, and forks or kills processes to
  99     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
 100     process is very self-regulating, it is rarely necessary to modify
 101     these directives from their default values. The maximum number of
 102     clients that may be served simultaneously (i.e., the maximum total
 103     number of threads in all processes) is determined by the
 104     <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> directive.
 105     The maximum number of active child processes is determined by
 106     the <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code>
 107     directive divided by the <code class="directive"><a href="../mod/mpm_common.html#&#10;    threadsperchild">
 108     ThreadsPerChild</a></code> directive.</p>
 109
 110     <p>Two directives set hard limits on the number of active child
 111     processes and the number of server threads in a child process,
 112     and can only be changed by fully stopping the server and then
 113     starting it again.  <code class="directive"><a href="../mod/mpm_common.html#serverlimit&#10;    ">ServerLimit
 114     </a></code> is a hard limit on the number of active child
 115     processes, and must be greater than or equal to the
 116     <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code>
 117     directive divided by the <code class="directive"><a href="../mod/mpm_common.html#&#10;    threadsperchild">
 118     ThreadsPerChild</a></code> directive.
 119     <code class="directive"><a href="../mod/mpm_common.html#threadlimit">ThreadLimit</a></code> is a hard
 120     limit of the number of server threads, and must be greater than
 121     or equal to the <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> directive.  If
 122     non-default values are specified for these directives, they
 123     should appear before other <code class="module"><a href="../mod/worker.html">worker</a></code> directives.</p>
 124
 125     <p>In addition to the set of active child processes, there may
 126     be additional child processes which are terminating, but where at
 127     least one server thread is still handling an existing client
 128     connection.  Up to <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> terminating processes
 129     may be present, though the actual number can be expected to be
 130     much smaller.  This behavior can be avoided by disabling the
 131     termination of individual child processes, which is achieved using
 132     the following:</p>
 133
 134     <ul>
 135       <li>set the value of <code class="directive"><a href="../mod/mpm_common.html#&#10;      maxrequestsperchild">
 136       MaxRequestsPerChild</a></code> to zero</li>
 137
 138       <li>set the value of <code class="directive"><a href="../mod/mpm_common.html#&#10;      maxsparethreads">
 139       MaxSpareThreads</a></code> to the same value as
 140       <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code></li>
 141     </ul>
 142
 143     <p>A typical configuration of the process-thread controls in
 144     the <code class="module"><a href="../mod/worker.html">worker</a></code> MPM could look as follows:</p>
 145
 146     <div class="example"><p><code>
 147       ServerLimit         16<br />
 148       StartServers         2<br />
 149       MaxClients         150<br />
 150       MinSpareThreads     25<br />
 151       MaxSpareThreads     75<br />
 152       ThreadsPerChild     25
 153     </code></p></div>
 154
 155     <p>While the parent process is usually started as <code>root</code>
 156     under Unix in order to bind to port 80, the child processes and threads
 157     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
 158     the privileges of the Apache child processes. The child processes
 159     must be able to read all the content that will be served, but
 160     should have as few privileges beyond that as possible. In
 161     addition, unless <code class="program"><a href="../programs/suexec.html">suexec</a></code> is used,
 162     these directives also set the privileges which will be inherited
 163     by CGI scripts.</p>
 164
 165     <p><code class="directive"><a href="../mod/mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</a></code>
 166     controls how frequently the server recycles processes by killing
 167     old ones and launching new ones.</p>
 168 </div>
 169 </div>
 170 <div class="bottomlang">
 171 <p><span>Available Languages: </span><a href="../de/mod/worker.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
 172 <a href="../en/mod/worker.html" title="English">&nbsp;en&nbsp;</a> |
 173 <a href="../ja/mod/worker.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a></p>
 174 </div><div id="footer">
 175 <p class="apache">Copyright 1995-2006 The Apache Software Foundation or its licensors, as applicable.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
 176 <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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