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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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30 <a href="../tr/mod/worker.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a></p>
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>
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>
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
53 <div id="quickview"><h3 class="directives">Directives</h3>
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>
78 <li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
79 </ul><h3>See also</h3>
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>
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>
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# threadsperchild">
109 ThreadsPerChild</a></code> directive.</p>
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 ">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# 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>
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
134 <li>set the value of <code class="directive"><a href="../mod/mpm_common.html# maxconnectionsperchild">
135 MaxConnectionsPerChild</a></code> to zero</li>
137 <li>set the value of <code class="directive"><a href="../mod/mpm_common.html# 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>
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>
145 <pre class="prettyprint lang-config">
148 MaxRequestWorkers 150
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
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>
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>
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