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16 <p class="apache">Apache HTTP Server Version 2.0</p>
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22 <div id="preamble"><h1>Apache MPM worker</h1>
24 <p><span>Available Languages: </span><a href="../de/mod/worker.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> |
25 <a href="../en/mod/worker.html" title="English"> en </a> |
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30 <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Multi-Processing Module implementing a hybrid
31 multi-threaded multi-process web server</td></tr>
32 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr>
33 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>mpm_worker_module</td></tr>
34 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>worker.c</td></tr></table>
37 <p>This Multi-Processing Module (MPM) implements a hybrid
38 multi-process multi-threaded server. By using threads to serve
39 requests, it is able to serve a large number of requests with
40 less system resources than a process-based server. Yet it
41 retains much of the stability of a process-based server by
42 keeping multiple processes available, each with many threads.</p>
44 <p>The most important directives used to control this MPM are
45 <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code>, which
46 controls the number of threads deployed by each child process and
47 <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code>, which
48 controls the maximum total number of threads that may be
51 <div id="quickview"><h3 class="directives">Directives</h3>
53 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#acceptmutex">AcceptMutex</a></li>
54 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li>
55 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#enableexceptionhook">EnableExceptionHook</a></li>
56 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#group">Group</a></li>
57 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li>
58 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li>
59 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#lockfile">LockFile</a></li>
60 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxclients">MaxClients</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#maxrequestsperchild">MaxRequestsPerChild</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#user">User</a></li>
77 <li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
78 </ul><h3>See also</h3>
80 <li><a href="../bind.html">Setting which addresses and ports Apache
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 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. Then during operation, Apache 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#maxclients">MaxClients</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#maxclients">MaxClients</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#maxclients">MaxClients</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. If
123 non-default values are specified for these directives, they
124 should appear before other <code class="module"><a href="../mod/worker.html">worker</a></code> directives.</p>
126 <p>In addition to the set of active child processes, there may
127 be additional child processes which are terminating but where at
128 least one server thread is still handling an existing client
129 connection. Up to <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> terminating processes
130 may be present, though the actual number can be expected to be
131 much smaller. This behavior can be avoided by disabling the
132 termination of individual child processes, which is achieved by
136 <li>set the value of <code class="directive"><a href="../mod/mpm_common.html# maxrequestsperchild">
137 MaxRequestsPerChild</a></code> to zero</li>
139 <li>set the value of <code class="directive"><a href="../mod/mpm_common.html# maxsparethreads">
140 MaxSpareThreads</a></code> to the same value as
141 <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code></li>
144 <p>A typical configuration of the process-thread controls in
145 the <code class="module"><a href="../mod/worker.html">worker</a></code> MPM could look as follows:</p>
147 <div class="example"><p><code>
151 MinSpareThreads 25<br />
152 MaxSpareThreads 75<br />
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 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
159 the privileges of the Apache 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#maxrequestsperchild">MaxRequestsPerChild</a></code>
167 controls how frequently the server recycles processes by killing
168 old ones and launching new ones.</p>
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178 <p class="apache">Copyright 2009 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>
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