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19 <p class="apache">Apache HTTP Server Version 2.4</p>
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23 <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 2.4</a> > <a href="./">Modules</a></div>
24 <div id="page-content">
25 <div id="preamble"><h1>Apache MPM worker</h1>
27 <p><span>Available Languages: </span><a href="../de/mod/worker.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> |
28 <a href="../en/mod/worker.html" title="English"> en </a> |
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33 <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Multi-Processing Module implementing a hybrid
34 multi-threaded multi-process web server</td></tr>
35 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr>
36 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>mpm_worker_module</td></tr>
37 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>worker.c</td></tr></table>
40 <p>This Multi-Processing Module (MPM) implements a hybrid
41 multi-process multi-threaded server. By using threads to serve
42 requests, it is able to serve a large number of requests with
43 fewer system resources than a process-based server. However, it
44 retains much of the stability of a process-based server by
45 keeping multiple processes available, each with many threads.</p>
47 <p>The most important directives used to control this MPM are
48 <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code>, which
49 controls the number of threads deployed by each child process and
50 <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>, which
51 controls the maximum total number of threads that may be
54 <div id="quickview"><h3 class="directives">Directives</h3>
56 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li>
57 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#enableexceptionhook">EnableExceptionHook</a></li>
58 <li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#group">Group</a></li>
59 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li>
60 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li>
61 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</a></li>
62 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li>
63 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></li>
64 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxsparethreads">MaxSpareThreads</a></li>
65 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#minsparethreads">MinSpareThreads</a></li>
66 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li>
67 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#receivebuffersize">ReceiveBufferSize</a></li>
68 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li>
69 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
70 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li>
71 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li>
72 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadlimit">ThreadLimit</a></li>
73 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadsperchild">ThreadsPerChild</a></li>
74 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadstacksize">ThreadStackSize</a></li>
75 <li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#user">User</a></li>
79 <li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
80 </ul><h3>See also</h3>
82 <li><a href="../bind.html">Setting which addresses and ports Apache HTTP Server uses</a></li>
83 </ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
84 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
86 <h2><a name="how-it-works" id="how-it-works">How it Works</a></h2>
87 <p>A single control process (the parent) is responsible for launching
88 child processes. Each child process creates a fixed number of server
89 threads as specified in the <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> directive, as well
90 as a listener thread which listens for connections and passes them
91 to a server thread for processing when they arrive.</p>
93 <p>Apache HTTP Server always tries to maintain a pool of <dfn>spare</dfn> or
94 idle server threads, which stand ready to serve incoming
95 requests. In this way, clients do not need to wait for a new
96 threads or processes to be created before their requests can be
97 served. The number of processes that will initially launch is
98 set by the <code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code>
99 directive. During operation, the server assesses the total number
100 of idle threads in all processes, and forks or kills processes to
101 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
102 process is very self-regulating, it is rarely necessary to modify
103 these directives from their default values. The maximum number of
104 clients that may be served simultaneously (i.e., the maximum total
105 number of threads in all processes) is determined by the
106 <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> directive.
107 The maximum number of active child processes is determined by
108 the <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>
109 directive divided by the <code class="directive"><a href="../mod/mpm_common.html# threadsperchild">
110 ThreadsPerChild</a></code> directive.</p>
112 <p>Two directives set hard limits on the number of active child
113 processes and the number of server threads in a child process,
114 and can only be changed by fully stopping the server and then
115 starting it again. <code class="directive"><a href="../mod/mpm_common.html#serverlimit ">ServerLimit
116 </a></code> is a hard limit on the number of active child
117 processes, and must be greater than or equal to the
118 <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>
119 directive divided by the <code class="directive"><a href="../mod/mpm_common.html# threadsperchild">
120 ThreadsPerChild</a></code> directive.
121 <code class="directive"><a href="../mod/mpm_common.html#threadlimit">ThreadLimit</a></code> is a hard
122 limit of the number of server threads, and must be greater than
123 or equal to the <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> directive.</p>
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#maxrequestworkers">MaxRequestWorkers</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
135 <li>set the value of <code class="directive"><a href="../mod/mpm_common.html# maxconnectionsperchild">
136 MaxConnectionsPerChild</a></code> to zero</li>
138 <li>set the value of <code class="directive"><a href="../mod/mpm_common.html# maxsparethreads">
139 MaxSpareThreads</a></code> to the same value as
140 <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code></li>
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>
146 <pre class="prettyprint lang-config">
149 MaxRequestWorkers 150
156 <p>While the parent process is usually started as <code>root</code>
157 under Unix in order to bind to port 80, the child processes and threads
158 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
159 the privileges of the Apache HTTP Server child processes. The child processes
160 must be able to read all the content that will be served, but
161 should have as few privileges beyond that as possible. In
162 addition, unless <code class="program"><a href="../programs/suexec.html">suexec</a></code> is used,
163 these directives also set the privileges which will be inherited
166 <p><code class="directive"><a href="../mod/mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</a></code>
167 controls how frequently the server recycles processes by killing
168 old ones and launching new ones.</p>
170 <p>This MPM uses the <code>mpm-accept</code> mutex to serialize
171 access to incoming connections when subject to the thundering herd
172 problem (generally, when there are multiple listening sockets).
173 The implementation aspects of this mutex can be configured with the
174 <code class="directive"><a href="../mod/core.html#mutex">Mutex</a></code> directive. The <a href="../misc/perf-tuning.html">performance hints</a>
175 documentation has additional information about this mutex.</p>
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184 </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&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again 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 Freenode, or sent to our <a href="http://httpd.apache.org/lists.html">mailing lists</a>.</div>
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