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19 <p class="apache">Apache HTTP Server Version 2.5</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 2.5</a> > <a href="./">Modules</a></div>
24 <div id="page-content">
25 <div id="preamble"><h1>Apache MPM event</h1>
27 <p><span>Available Languages: </span><a href="../en/mod/event.html" title="English"> en </a> |
28 <a href="../fr/mod/event.html" hreflang="fr" rel="alternate" title="Français"> fr </a></p>
30 <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
31 of consuming threads only for connections with active processing</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_event_module</td></tr>
34 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>event.c</td></tr></table>
37 <p>The <code class="module"><a href="../mod/event.html">event</a></code> Multi-Processing Module (MPM) is
38 designed to allow more requests to be served simultaneously by
39 passing off some processing work to supporting threads, freeing up
40 the main threads to work on new requests. It is based on the
41 <code class="module"><a href="../mod/worker.html">worker</a></code> MPM, which implements a hybrid
42 multi-process multi-threaded server. Run-time configuration
43 directives are identical to those provided by
44 <code class="module"><a href="../mod/worker.html">worker</a></code>.</p>
46 <p>To use the <code class="module"><a href="../mod/event.html">event</a></code> MPM, add
47 <code>--with-mpm=event</code> to the <code class="program"><a href="../programs/configure.html">configure</a></code>
48 script's arguments when building the <code class="program"><a href="../programs/httpd.html">httpd</a></code>.</p>
51 <div id="quickview"><h3 class="directives">Directives</h3>
53 <li><img alt="" src="../images/down.gif" /> <a href="#asyncrequestworkerfactor">AsyncRequestWorkerFactor</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="mod_unixd.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#maxconnectionsperchild">MaxConnectionsPerChild</a></li>
60 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li>
61 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></li>
62 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxsparethreads">MaxSpareThreads</a></li>
63 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#minsparethreads">MinSpareThreads</a></li>
64 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li>
65 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li>
66 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
67 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li>
68 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li>
69 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadlimit">ThreadLimit</a></li>
70 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadsperchild">ThreadsPerChild</a></li>
71 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadstacksize">ThreadStackSize</a></li>
72 <li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#user">User</a></li>
76 <li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
77 <li><img alt="" src="../images/down.gif" /> <a href="#requirements">Requirements</a></li>
78 </ul><h3>See also</h3>
80 <li><a href="worker.html">The worker MPM</a></li>
81 </ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
82 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
84 <h2><a name="how-it-works" id="how-it-works">How it Works</a></h2>
85 <p>This MPM tries to fix the 'keep alive problem' in HTTP. After a client
86 completes the first request, the client can keep the connection
87 open, and send further requests using the same socket. This can
88 save significant overhead in creating TCP connections. However,
89 Apache HTTP Server traditionally keeps an entire child process/thread waiting
90 for data from the client, which brings its own disadvantages. To
91 solve this problem, this MPM uses a dedicated thread to handle both
92 the Listening sockets, all sockets that are in a Keep Alive state,
93 and sockets where the handler and protocol filters have done their work
94 and the only remaining thing to do is send the data to the client. The
95 status page of <code class="module"><a href="../mod/mod_status.html">mod_status</a></code> shows how many connections are
96 in the mentioned states.</p>
98 <p>The improved connection handling does not yet work for certain
99 connection filters, in particular SSL. For SSL connections, this MPM will
100 fall back to the behaviour of the <code class="module"><a href="../mod/worker.html">worker</a></code> MPM and
101 reserve one worker thread per connection.</p>
103 <p>The MPM assumes that the underlying <code>apr_pollset</code>
104 implementation is reasonably threadsafe. This enables the MPM to
105 avoid excessive high level locking, or having to wake up the listener
106 thread in order to send it a keep-alive socket. This is currently
107 only compatible with KQueue and EPoll.</p>
109 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
110 <div class="section">
111 <h2><a name="requirements" id="requirements">Requirements</a></h2>
112 <p>This MPM depends on <a class="glossarylink" href="../glossary.html#apr" title="see glossary">APR</a>'s atomic
113 compare-and-swap operations for thread synchronization. If you are
114 compiling for an x86 target and you don't need to support 386s, or
115 you are compiling for a SPARC and you don't need to run on
116 pre-UltraSPARC chips, add
117 <code>--enable-nonportable-atomics=yes</code> to the
118 <code class="program"><a href="../programs/configure.html">configure</a></code> script's arguments. This will cause
119 APR to implement atomic operations using efficient opcodes not
120 available in older CPUs.</p>
122 <p>This MPM does not perform well on older platforms which lack good
123 threading, but the requirement for EPoll or KQueue makes this
128 <li>To use this MPM on FreeBSD, FreeBSD 5.3 or higher is recommended.
129 However, it is possible to run this MPM on FreeBSD 5.2.1, if you
130 use <code>libkse</code> (see <code>man libmap.conf</code>).</li>
132 <li>For NetBSD, at least version 2.0 is recommended.</li>
134 <li>For Linux, a 2.6 kernel is recommended. It is also necessary to
135 ensure that your version of <code>glibc</code> has been compiled
136 with support for EPoll.</li>
140 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
141 <div class="directive-section"><h2><a name="AsyncRequestWorkerFactor" id="AsyncRequestWorkerFactor">AsyncRequestWorkerFactor</a> <a name="asyncrequestworkerfactor" id="asyncrequestworkerfactor">Directive</a></h2>
142 <table class="directive">
143 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Limit concurrent connections per process</td></tr>
144 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>AsyncRequestWorkerFactor <var>factor</var></code></td></tr>
145 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>2</code></td></tr>
146 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
147 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
148 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>event</td></tr>
149 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.3.13 and later</td></tr>
151 <p>The event MPM handles some connections in an asynchronous way, where
152 request worker threads are only allocated for short periods of time as
153 needed, and other (mostly SSL) connections with one request worker thread
154 reserved per connection. This can lead to situations where all workers are
155 tied up and no worker thread is available to handle new work on established
156 async connections.</p>
158 <p>To mitigate this problem, the event MPM does two things: Firstly, it
159 limits the number of connections accepted per process, depending on the
160 number of idle request workers. Secondly, if all workers are busy, it will
161 close connections in keep-alive state even if the keep-alive timeout has
162 not expired. This allows the respective clients to reconnect to a
163 different process which may still have worker threads available.</p>
165 <p>This directive can be used to fine-tune the per-process connection
166 limit. A process will only accept new connections if the current number of
167 connections is lower than:</p>
169 <p class="indent"><strong>
170 <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> +
171 (<code class="directive">AsyncRequestWorkerFactor</code> *
172 <var>number of idle workers</var>)
175 <p>This means the absolute maximum numbers of concurrent connections is:</p>
177 <p class="indent"><strong>
178 (<code class="directive">AsyncRequestWorkerFactor</code> + 1) *
179 <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>
182 <p><code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> was called
183 <code class="directive">MaxClients</code> prior to version 2.3.13. The above value
184 shows that the old name did not accurately describe its meaning for the event MPM.</p>
186 <p><code class="directive">AsyncRequestWorkerFactor</code> can take non-integer
187 arguments, e.g "1.5".</p>
192 <div class="bottomlang">
193 <p><span>Available Languages: </span><a href="../en/mod/event.html" title="English"> en </a> |
194 <a href="../fr/mod/event.html" hreflang="fr" rel="alternate" title="Français"> fr </a></p>
195 </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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