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8 <title>event - Apache HTTP Server</title>
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16 <p class="apache">Apache HTTP Server Version 2.3</p>
17 <img alt="" src="../images/feather.gif" /></div>
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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/">Documentation</a> > <a href="../">Version 2.3</a> > <a href="./">Modules</a></div>
21 <div id="page-content">
22 <div id="preamble"><h1>Apache MPM event</h1>
24 <p><span>Available Languages: </span><a href="../en/mod/event.html" title="English"> en </a> |
25 <a href="../fr/mod/event.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
26 <a href="../zh-cn/mod/event.html" hreflang="zh-cn" rel="alternate" title="Simplified Chinese"> zh-cn </a></p>
28 <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>A variant of the <code class="module"><a href="../mod/worker.html">worker</a></code> MPM with the goal
29 of consuming threads only for connections with active processing</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_event_module</td></tr>
32 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>event.c</td></tr></table>
35 <p>The <code class="module"><a href="../mod/event.html">event</a></code> Multi-Processing Module (MPM) is
36 designed to allow more requests to be served simultaneously by
37 passing off some processing work to supporting threads, freeing up
38 the main threads to work on new requests. It is based on the
39 <code class="module"><a href="../mod/worker.html">worker</a></code> MPM, which implements a hybrid
40 multi-process multi-threaded server. Run-time configuration
41 directives are identical to those provided by
42 <code class="module"><a href="../mod/worker.html">worker</a></code>.</p>
44 <p>To use the <code class="module"><a href="../mod/event.html">event</a></code> MPM, add
45 <code>--with-mpm=event</code> to the <code class="program"><a href="../programs/configure.html">configure</a></code>
46 script's arguments when building the <code class="program"><a href="../programs/httpd.html">httpd</a></code>.</p>
49 <div id="quickview"><h3 class="directives">Directives</h3>
51 <li><img alt="" src="../images/down.gif" /> <a href="#asyncrequestworkerfactor">AsyncRequestWorkerFactor</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#maxconnectionsperchild">MaxConnectionsPerChild</a></li>
58 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li>
59 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></li>
60 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxsparethreads">MaxSpareThreads</a></li>
61 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#minsparethreads">MinSpareThreads</a></li>
62 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li>
63 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li>
64 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
65 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li>
66 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li>
67 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadlimit">ThreadLimit</a></li>
68 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadsperchild">ThreadsPerChild</a></li>
69 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadstacksize">ThreadStackSize</a></li>
70 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#user">User</a></li>
74 <li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
75 <li><img alt="" src="../images/down.gif" /> <a href="#requirements">Requirements</a></li>
76 </ul><h3>See also</h3>
78 <li><a href="worker.html">The worker MPM</a></li>
80 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
82 <h2><a name="how-it-works" id="how-it-works">How it Works</a></h2>
83 <p>This MPM tries to fix the 'keep alive problem' in HTTP. After a client
84 completes the first request, the client can keep the connection
85 open, and send further requests using the same socket. This can
86 save signifigant overhead in creating TCP connections. However,
87 Apache HTTP Server traditionally keeps an entire child process/thread waiting
88 for data from the client, which brings its own disadvantages. To
89 solve this problem, this MPM uses a dedicated thread to handle both
90 the Listening sockets, all sockets that are in a Keep Alive state,
91 and sockets where the handler and protocol filters have done their work
92 and the only remaining thing to do is send the data to the client. The
93 status page of <code class="module"><a href="../mod/mod_status.html">mod_status</a></code> shows how many connections are
94 in the mentioned states.</p>
96 <p>The improved connection handling does not yet work for certain
97 connection filters, in particular SSL. For SSL connections, this MPM will
98 fall back to the behaviour of the <code class="module"><a href="../mod/worker.html">worker</a></code> MPM and
99 reserve one worker thread per connection.</p>
101 <p>The MPM assumes that the underlying <code>apr_pollset</code>
102 implementation is reasonably threadsafe. This enables the MPM to
103 avoid excessive high level locking, or having to wake up the listener
104 thread in order to send it a keep-alive socket. This is currently
105 only compatible with KQueue and EPoll.</p>
107 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
108 <div class="section">
109 <h2><a name="requirements" id="requirements">Requirements</a></h2>
110 <p>This MPM depends on <a class="glossarylink" href="../glossary.html#apr" title="see glossary">APR</a>'s atomic
111 compare-and-swap operations for thread synchronization. If you are
112 compiling for an x86 target and you don't need to support 386s, or
113 you are compiling for a SPARC and you don't need to run on
114 pre-UltraSPARC chips, add
115 <code>--enable-nonportable-atomics=yes</code> to the
116 <code class="program"><a href="../programs/configure.html">configure</a></code> script's arguments. This will cause
117 APR to implement atomic operations using efficient opcodes not
118 available in older CPUs.</p>
120 <p>This MPM does not perform well on older platforms which lack good
121 threading, but the requirement for EPoll or KQueue makes this
126 <li>To use this MPM on FreeBSD, FreeBSD 5.3 or higher is recommended.
127 However, it is possible to run this MPM on FreeBSD 5.2.1, if you
128 use <code>libkse</code> (see <code>man libmap.conf</code>).</li>
130 <li>For NetBSD, at least version 2.0 is recommended.</li>
132 <li>For Linux, a 2.6 kernel is recommended. It is also necessary to
133 ensure that your version of <code>glibc</code> has been compiled
134 with support for EPoll.</li>
138 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
139 <div class="directive-section"><h2><a name="AsyncRequestWorkerFactor" id="AsyncRequestWorkerFactor">AsyncRequestWorkerFactor</a> <a name="asyncrequestworkerfactor" id="asyncrequestworkerfactor">Directive</a></h2>
140 <table class="directive">
141 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Limit concurrent connections per process</td></tr>
142 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>AsyncRequestWorkerFactor <var>factor</var></code></td></tr>
143 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>2</code></td></tr>
144 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
145 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
146 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>event</td></tr>
147 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.3.13 and later</td></tr>
149 <p>The event MPM handles some connections in an asynchronous way, where
150 request worker threads are only allocated for short periods of time as
151 needed, and other (mostly SSL) connections with one request worker thread
152 reserved per connection. This can lead to situations where all workers are
153 tied up and no worker thread is available to handle new work on established
154 async connetions.</p>
156 <p>To mitigate this problem, the event MPM does two things: Firstly, it
157 limits the number of connections accepted per process, depending on the
158 number of idle request workers. Secondly, if all workers are busy, it will
159 close connections in keep-alive state even if the keep-alive timeout has
160 not expired. This allows the respective clients to reconnect to a
161 different process which may still have worker threads available.</p>
163 <p>This directive can be used to fine-tune the per-process connection
164 limit. A process will only accept new connections if the current number of
165 connections is lower than:</p>
167 <p class="indent"><strong>
168 <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> +
169 (<code class="directive">AsyncRequestWorkerFactor</code> *
170 <var>number of idle workers</var>)
173 <p>This means the absolute maximum numbers of concurrent connections is:</p>
175 <p class="indent"><strong>
176 (<code class="directive">AsyncRequestWorkerFactor</code> + 1) *
177 <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>
180 <p><code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> was called
181 <code class="directive">MaxClients</code> prior to version 2.3.13. The above value
182 shows that the old name did not accurately describe its meaning for the event MPM.</p>
184 <p><code class="directive">AsyncRequestWorkerFactor</code> can take non-integer
185 arguments, e.g "1.5".</p>
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191 <p><span>Available Languages: </span><a href="../en/mod/event.html" title="English"> en </a> |
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194 </div><div id="footer">
195 <p class="apache">Copyright 2011 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>
196 <p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p></div>