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  19 <p class="apache">Apache HTTP Server Version 2.5</p>
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  23 <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 2.5</a> &gt; <a href="./">Modules</a></div>
  24 <div id="page-content">
  25 <div id="preamble"><h1>Apache MPM worker</h1>
  26 <div class="toplang">
  27 <p><span>Available Languages: </span><a href="../de/mod/worker.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
  28 <a href="../en/mod/worker.html" title="English">&nbsp;en&nbsp;</a> |
  29 <a href="../ja/mod/worker.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
  30 <a href="../tr/mod/worker.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a></p>
  31 </div>
  32 <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Multi-Processing Module implementing a hybrid
  33     multi-threaded multi-process web server</td></tr>
  34 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr>
  35 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>mpm_worker_module</td></tr>
  36 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>worker.c</td></tr></table>
  37 <h3>Summary</h3>
  38
  39     <p>This Multi-Processing Module (MPM) implements a hybrid
  40     multi-process multi-threaded server. By using threads to serve
  41     requests, it is able to serve a large number of requests with
  42     fewer system resources than a process-based server. However, it
  43     retains much of the stability of a process-based server by
  44     keeping multiple processes available, each with many threads.</p>
  45
  46     <p>The most important directives used to control this MPM are
  47     <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code>, which
  48     controls the number of threads deployed by each child process and
  49     <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>, which
  50     controls the maximum total number of threads that may be
  51     launched.</p>
  52 </div>
  53 <div id="quickview"><h3 class="directives">Directives</h3>
  54 <ul id="toc">
  55 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li>
  56 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#enableexceptionhook">EnableExceptionHook</a></li>
  57 <li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#group">Group</a></li>
  58 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li>
  59 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li>
  60 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</a></li>
  61 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li>
  62 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></li>
  63 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxsparethreads">MaxSpareThreads</a></li>
  64 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#minsparethreads">MinSpareThreads</a></li>
  65 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li>
  66 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#receivebuffersize">ReceiveBufferSize</a></li>
  67 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li>
  68 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
  69 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li>
  70 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li>
  71 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadlimit">ThreadLimit</a></li>
  72 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadsperchild">ThreadsPerChild</a></li>
  73 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadstacksize">ThreadStackSize</a></li>
  74 <li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#user">User</a></li>
  75 </ul>
  76 <h3>Topics</h3>
  77 <ul id="topics">
  78 <li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
  79 </ul><h3>See also</h3>
  80 <ul class="seealso">
  81 <li><a href="../bind.html">Setting which addresses and ports Apache HTTP Server uses</a></li>
  82 </ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
  83 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
  84 <div class="section">
  85 <h2><a name="how-it-works" id="how-it-works">How it Works</a></h2>
  86     <p>A single control process (the parent) is responsible for launching
  87     child processes. Each child process creates a fixed number of server
  88     threads as specified in the <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> directive, as well
  89     as a listener thread which listens for connections and passes them
  90     to a server thread for processing when they arrive.</p>
  91
  92     <p>Apache HTTP Server always tries to maintain a pool of <dfn>spare</dfn> or
  93     idle server threads, which stand ready to serve incoming
  94     requests. In this way, clients do not need to wait for a new
  95     threads or processes to be created before their requests can be
  96     served. The number of processes that will initially launched is
  97     set by the <code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code>
  98     directive. During operation, the server assesses the total number
  99     of idle threads in all processes, and forks or kills processes to
 100     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
 101     process is very self-regulating, it is rarely necessary to modify
 102     these directives from their default values. The maximum number of
 103     clients that may be served simultaneously (i.e., the maximum total
 104     number of threads in all processes) is determined by the
 105     <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> directive.
 106     The maximum number of active child processes is determined by
 107     the <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>
 108     directive divided by the <code class="directive"><a href="../mod/mpm_common.html#&#10;    threadsperchild">
 109     ThreadsPerChild</a></code> directive.</p>
 110
 111     <p>Two directives set hard limits on the number of active child
 112     processes and the number of server threads in a child process,
 113     and can only be changed by fully stopping the server and then
 114     starting it again.  <code class="directive"><a href="../mod/mpm_common.html#serverlimit&#10;    ">ServerLimit
 115     </a></code> is a hard limit on the number of active child
 116     processes, and must be greater than or equal to the
 117     <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>
 118     directive divided by the <code class="directive"><a href="../mod/mpm_common.html#&#10;    threadsperchild">
 119     ThreadsPerChild</a></code> directive.
 120     <code class="directive"><a href="../mod/mpm_common.html#threadlimit">ThreadLimit</a></code> is a hard
 121     limit of the number of server threads, and must be greater than
 122     or equal to the <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> directive.</p>
 123
 124     <p>In addition to the set of active child processes, there may
 125     be additional child processes which are terminating, but where at
 126     least one server thread is still handling an existing client
 127     connection.  Up to <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> terminating processes
 128     may be present, though the actual number can be expected to be
 129     much smaller.  This behavior can be avoided by disabling the
 130     termination of individual child processes, which is achieved using
 131     the following:</p>
 132
 133     <ul>
 134       <li>set the value of <code class="directive"><a href="../mod/mpm_common.html#&#10;      maxconnectionsperchild">
 135       MaxConnectionsPerChild</a></code> to zero</li>
 136
 137       <li>set the value of <code class="directive"><a href="../mod/mpm_common.html#&#10;      maxsparethreads">
 138       MaxSpareThreads</a></code> to the same value as
 139       <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code></li>
 140     </ul>
 141
 142     <p>A typical configuration of the process-thread controls in
 143     the <code class="module"><a href="../mod/worker.html">worker</a></code> MPM could look as follows:</p>
 144
 145     <pre class="prettyprint lang-config">
 146 ServerLimit         16
 147 StartServers         2
 148 MaxRequestWorkers  150
 149 MinSpareThreads     25
 150 MaxSpareThreads     75
 151 ThreadsPerChild     25
 152     </pre>
 153
 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 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
 158     the privileges of the Apache HTTP Server 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#maxconnectionsperchild">MaxConnectionsPerChild</a></code>
 166     controls how frequently the server recycles processes by killing
 167     old ones and launching new ones.</p>
 168
 169     <p>This MPM uses the <code>mpm-accept</code> mutex to serialize
 170     access to incoming connections when subject to the thundering herd
 171     problem (generally, when there are multiple listening sockets).
 172     The implementation aspects of this mutex can be configured with the
 173     <code class="directive"><a href="../mod/core.html#mutex">Mutex</a></code> directive.  The <a href="../misc/perf-tuning.html">performance hints</a>
 174     documentation has additional information about this mutex.</p>
 175 </div>
 176 </div>
 177 <div class="bottomlang">
 178 <p><span>Available Languages: </span><a href="../de/mod/worker.html" hreflang="de" rel="alternate" title="Deutsch">&nbsp;de&nbsp;</a> |
 179 <a href="../en/mod/worker.html" title="English">&nbsp;en&nbsp;</a> |
 180 <a href="../ja/mod/worker.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
 181 <a href="../tr/mod/worker.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a></p>
 182 </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>This section is experimental!</strong><br />Comments placed here should not be expected
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