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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>Topics</h3>
53 <li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
54 <li><img alt="" src="../images/down.gif" /> <a href="#requirements">Requirements</a></li>
55 </ul><h3 class="directives">Directives</h3>
57 <li><img alt="" src="../images/down.gif" /> <a href="#asyncrequestworkerfactor">AsyncRequestWorkerFactor</a></li>
58 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li>
59 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#enableexceptionhook">EnableExceptionHook</a></li>
60 <li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#group">Group</a></li>
61 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li>
62 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li>
63 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</a></li>
64 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li>
65 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></li>
66 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxsparethreads">MaxSpareThreads</a></li>
67 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#minsparethreads">MinSpareThreads</a></li>
68 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li>
69 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li>
70 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
71 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li>
72 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li>
73 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadlimit">ThreadLimit</a></li>
74 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadsperchild">ThreadsPerChild</a></li>
75 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadstacksize">ThreadStackSize</a></li>
76 <li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#user">User</a></li>
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 may not work for certain connection
99 filters that have declared themselves as incompatible with event. In these
100 cases, this MPM will fall back to the behaviour of the
101 <code class="module"><a href="../mod/worker.html">worker</a></code> MPM and reserve one worker thread per connection.
102 All modules shipped with the server are compatible with the event MPM.</p>
104 <p>A similar restriction is currently present for requests involving an
105 output filter that needs to read and/or modify the whole response body,
106 like for example mod_ssl, mod_deflate, or mod_include. If the
107 connection to the client blocks while the filter is processing the
108 data, and the amount of data produced by the filter is too big to be
109 buffered in memory, the thread used for the request is not freed while
110 httpd waits until the pending data is sent to the client.</p>
112 <p>The MPM assumes that the underlying <code>apr_pollset</code>
113 implementation is reasonably threadsafe. This enables the MPM to
114 avoid excessive high level locking, or having to wake up the listener
115 thread in order to send it a keep-alive socket. This is currently
116 only compatible with KQueue and EPoll.</p>
118 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
119 <div class="section">
120 <h2><a name="requirements" id="requirements">Requirements</a></h2>
121 <p>This MPM depends on <a class="glossarylink" href="../glossary.html#apr" title="see glossary">APR</a>'s atomic
122 compare-and-swap operations for thread synchronization. If you are
123 compiling for an x86 target and you don't need to support 386s, or
124 you are compiling for a SPARC and you don't need to run on
125 pre-UltraSPARC chips, add
126 <code>--enable-nonportable-atomics=yes</code> to the
127 <code class="program"><a href="../programs/configure.html">configure</a></code> script's arguments. This will cause
128 APR to implement atomic operations using efficient opcodes not
129 available in older CPUs.</p>
131 <p>This MPM does not perform well on older platforms which lack good
132 threading, but the requirement for EPoll or KQueue makes this
137 <li>To use this MPM on FreeBSD, FreeBSD 5.3 or higher is recommended.
138 However, it is possible to run this MPM on FreeBSD 5.2.1, if you
139 use <code>libkse</code> (see <code>man libmap.conf</code>).</li>
141 <li>For NetBSD, at least version 2.0 is recommended.</li>
143 <li>For Linux, a 2.6 kernel is recommended. It is also necessary to
144 ensure that your version of <code>glibc</code> has been compiled
145 with support for EPoll.</li>
149 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
150 <div class="directive-section"><h2><a name="AsyncRequestWorkerFactor" id="AsyncRequestWorkerFactor">AsyncRequestWorkerFactor</a> <a name="asyncrequestworkerfactor" id="asyncrequestworkerfactor">Directive</a></h2>
151 <table class="directive">
152 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Limit concurrent connections per process</td></tr>
153 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>AsyncRequestWorkerFactor <var>factor</var></code></td></tr>
154 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>2</code></td></tr>
155 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
156 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
157 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>event</td></tr>
158 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.3.13 and later</td></tr>
160 <p>The event MPM handles some connections in an asynchronous way, where
161 request worker threads are only allocated for short periods of time as
162 needed, and other connections with one request worker thread reserved per
163 connection. This can lead to situations where all workers are tied up and
164 no worker thread is available to handle new work on established async
167 <p>To mitigate this problem, the event MPM does two things: Firstly, it
168 limits the number of connections accepted per process, depending on the
169 number of idle request workers. Secondly, if all workers are busy, it will
170 close connections in keep-alive state even if the keep-alive timeout has
171 not expired. This allows the respective clients to reconnect to a
172 different process which may still have worker threads available.</p>
174 <p>This directive can be used to fine-tune the per-process connection
175 limit. A process will only accept new connections if the current number of
176 connections (not counting connections in the "closing" state) is lower
179 <p class="indent"><strong>
180 <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> +
181 (<code class="directive">AsyncRequestWorkerFactor</code> *
182 <var>number of idle workers</var>)
185 <p>This means the absolute maximum numbers of concurrent connections is:</p>
187 <p class="indent"><strong>
188 (<code class="directive">AsyncRequestWorkerFactor</code> + 1) *
189 <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>
192 <p><code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> was called
193 <code class="directive">MaxClients</code> prior to version 2.3.13. The above value
194 shows that the old name did not accurately describe its meaning for the event MPM.</p>
196 <p><code class="directive">AsyncRequestWorkerFactor</code> can take non-integer
197 arguments, e.g "1.5".</p>
202 <div class="bottomlang">
203 <p><span>Available Languages: </span><a href="../en/mod/event.html" title="English"> en </a> |
204 <a href="../fr/mod/event.html" hreflang="fr" rel="alternate" title="Français"> fr </a></p>
205 </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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