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16 <p class="apache">Apache HTTP Server Version 2.1</p>
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20 <a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs-project/">Documentation</a> > <a href="../">Version 2.1</a> > <a href="./">Modules</a></div>
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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> |
26 <a href="../ja/mod/worker.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a></p>
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>
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 less system resources than a process-based server. Yet it
39 retains much of the stability of a process-based server by
40 keeping multiple processes available, each with many threads.</p>
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
49 <div id="quickview"><h3 class="directives">Directives</h3>
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#scoreboardfile">ScoreBoardFile</a></li>
65 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
66 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li>
67 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li>
68 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadlimit">ThreadLimit</a></li>
69 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadsperchild">ThreadsPerChild</a></li>
70 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadstacksize">ThreadStackSize</a></li>
71 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#user">User</a></li>
75 <li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
76 </ul><h3>See also</h3>
78 <li><a href="../bind.html">Setting which addresses and ports Apache
81 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
83 <h2><a name="how-it-works" id="how-it-works">How it Works</a></h2>
84 <p>A single control process (the parent) is responsible for launching
85 child processes. Each child process creates a fixed number of server
86 threads as specified in the <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> directive, as well
87 as a listener thread which listens for connections and passes them
88 to a server thread for processing when they arrive.</p>
90 <p>Apache always tries to maintain a pool of <dfn>spare</dfn> or
91 idle server threads, which stand ready to serve incoming
92 requests. In this way, clients do not need to wait for a new
93 threads or processes to be created before their requests can be
94 served. The number of processes that will initially launched is
95 set by the <code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code>
96 directive. Then during operation, Apache assesses the total number
97 of idle threads in all processes, and forks or kills processes to
98 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
99 process is very self-regulating, it is rarely necessary to modify
100 these directives from their default values. The maximum number of
101 clients that may be served simultaneously (i.e., the maximum total
102 number of threads in all processes) is determined by the
103 <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code> directive.
104 The maximum number of active child processes is determined by
105 the <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code>
106 directive divided by the <code class="directive"><a href="../mod/mpm_common.html# threadsperchild">
107 ThreadsPerChild</a></code> directive.</p>
109 <p>Two directives set hard limits on the number of active child
110 processes and the number of server threads in a child process,
111 and can only be changed by fully stopping the server and then
112 starting it again. <code class="directive"><a href="../mod/mpm_common.html#serverlimit ">ServerLimit
113 </a></code> is a hard limit on the number of active child
114 processes, and must be greater than or equal to the
115 <code class="directive"><a href="../mod/mpm_common.html#maxclients">MaxClients</a></code>
116 directive divided by the <code class="directive"><a href="../mod/mpm_common.html# threadsperchild">
117 ThreadsPerChild</a></code> directive.
118 <code class="directive"><a href="../mod/mpm_common.html#threadlimit">ThreadLimit</a></code> is a hard
119 limit of the number of server threads, and must be greater than
120 or equal to the <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> directive. If
121 non-default values are specified for these directives, they
122 should appear before other <code class="module"><a href="../mod/worker.html">worker</a></code> directives.</p>
124 <p>In addition to a 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#maxclients">MaxClients</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 by
134 <li>set the value of <code class="directive"><a href="../mod/mpm_common.html# maxrequestsperchild">
135 MaxRequestsPerChild</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#maxclients">MaxClients</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 <div class="example"><p><code>
149 MinSpareThreads 25<br />
150 MaxSpareThreads 75<br />
154 <p>While the parent process is usually started as <code>root</code>
155 under Unix in order to bind to port 80, the child processes and threads
156 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
157 the privileges of the Apache child processes. The child processes
158 must be able to read all the content that will be served, but
159 should have as few privileges beyond that as possible. In
160 addition, unless <a href="../suexec.html">suexec</a> is used,
161 these directives also set the privileges which will be inherited
164 <p><code class="directive"><a href="../mod/mpm_common.html#maxrequestsperchild">MaxRequestsPerChild</a></code>
165 controls how frequently the server recycles processes by killing
166 old ones and launching new ones.</p>
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174 <p class="apache">Copyright 1999-2004 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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