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231 lines
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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<meta content="text/html; charset=ISO-8859-1" http-equiv="Content-Type" />
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<!--
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This file is generated from xml source: DO NOT EDIT
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<title>event - Apache HTTP Server Version 2.5</title>
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<link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
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<link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" />
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</script>
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<link href="../images/favicon.ico" rel="shortcut icon" /></head>
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<body>
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<div id="page-header">
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<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/quickreference.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
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<p class="apache">Apache HTTP Server Version 2.5</p>
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<img alt="" src="../images/feather.gif" /></div>
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<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
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<div id="path">
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<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>
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<div id="page-content">
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<div id="preamble"><h1>Apache MPM event</h1>
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<div class="toplang">
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<p><span>Available Languages: </span><a href="../en/mod/event.html" title="English"> en </a> |
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<a href="../fr/mod/event.html" hreflang="fr" rel="alternate" title="Fran<61>ais"> fr </a></p>
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</div>
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<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
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of consuming threads only for connections with active processing</td></tr>
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<tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr>
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<tr><th><a href="module-dict.html#ModuleIdentifier">Module<EFBFBD>Identifier:</a></th><td>mpm_event_module</td></tr>
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<tr><th><a href="module-dict.html#SourceFile">Source<EFBFBD>File:</a></th><td>event.c</td></tr></table>
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<h3>Summary</h3>
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<p>The <code class="module"><a href="../mod/event.html">event</a></code> Multi-Processing Module (MPM) is
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designed to allow more requests to be served simultaneously by
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passing off some processing work to supporting threads, freeing up
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the main threads to work on new requests. It is based on the
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<code class="module"><a href="../mod/worker.html">worker</a></code> MPM, which implements a hybrid
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multi-process multi-threaded server. Run-time configuration
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directives are identical to those provided by
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<code class="module"><a href="../mod/worker.html">worker</a></code>.</p>
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<p>To use the <code class="module"><a href="../mod/event.html">event</a></code> MPM, add
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<code>--with-mpm=event</code> to the <code class="program"><a href="../programs/configure.html">configure</a></code>
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script's arguments when building the <code class="program"><a href="../programs/httpd.html">httpd</a></code>.</p>
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</div>
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<div id="quickview"><h3>Topics</h3>
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<ul id="topics">
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<li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#requirements">Requirements</a></li>
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</ul><h3 class="directives">Directives</h3>
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<ul id="toc">
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<li><img alt="" src="../images/down.gif" /> <a href="#asyncrequestworkerfactor">AsyncRequestWorkerFactor</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#enableexceptionhook">EnableExceptionHook</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#group">Group</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxsparethreads">MaxSpareThreads</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#minsparethreads">MinSpareThreads</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadlimit">ThreadLimit</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadsperchild">ThreadsPerChild</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadstacksize">ThreadStackSize</a></li>
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<li><img alt="" src="../images/right.gif" /> <a href="mod_unixd.html#user">User</a></li>
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</ul>
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<h3>See also</h3>
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<ul class="seealso">
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<li><a href="worker.html">The worker MPM</a></li>
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</ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="section">
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<h2><a name="how-it-works" id="how-it-works">How it Works</a></h2>
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<p>This MPM tries to fix the 'keep alive problem' in HTTP. After a client
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completes the first request, the client can keep the connection
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open, and send further requests using the same socket. This can
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save significant overhead in creating TCP connections. However,
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Apache HTTP Server traditionally keeps an entire child process/thread waiting
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for data from the client, which brings its own disadvantages. To
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solve this problem, this MPM uses a dedicated thread to handle both
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the Listening sockets, all sockets that are in a Keep Alive state,
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and sockets where the handler and protocol filters have done their work
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and the only remaining thing to do is send the data to the client. The
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status page of <code class="module"><a href="../mod/mod_status.html">mod_status</a></code> shows how many connections are
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in the mentioned states.</p>
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<p>The improved connection handling may not work for certain connection
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filters that have declared themselves as incompatible with event. In these
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cases, this MPM will fall back to the behaviour of the
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<code class="module"><a href="../mod/worker.html">worker</a></code> MPM and reserve one worker thread per connection.
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All modules shipped with the server are compatible with the event MPM.</p>
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<p>A similar restriction is currently present for requests involving an
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output filter that needs to read and/or modify the whole response body,
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like for example mod_ssl, mod_deflate, or mod_include. If the
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connection to the client blocks while the filter is processing the
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data, and the amount of data produced by the filter is too big to be
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buffered in memory, the thread used for the request is not freed while
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httpd waits until the pending data is sent to the client.</p>
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<p>The MPM assumes that the underlying <code>apr_pollset</code>
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implementation is reasonably threadsafe. This enables the MPM to
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avoid excessive high level locking, or having to wake up the listener
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thread in order to send it a keep-alive socket. This is currently
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only compatible with KQueue and EPoll.</p>
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</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="section">
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<h2><a name="requirements" id="requirements">Requirements</a></h2>
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<p>This MPM depends on <a class="glossarylink" href="../glossary.html#apr" title="see glossary">APR</a>'s atomic
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compare-and-swap operations for thread synchronization. If you are
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compiling for an x86 target and you don't need to support 386s, or
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you are compiling for a SPARC and you don't need to run on
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pre-UltraSPARC chips, add
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<code>--enable-nonportable-atomics=yes</code> to the
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<code class="program"><a href="../programs/configure.html">configure</a></code> script's arguments. This will cause
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APR to implement atomic operations using efficient opcodes not
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available in older CPUs.</p>
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<p>This MPM does not perform well on older platforms which lack good
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threading, but the requirement for EPoll or KQueue makes this
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moot.</p>
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<ul>
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<li>To use this MPM on FreeBSD, FreeBSD 5.3 or higher is recommended.
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However, it is possible to run this MPM on FreeBSD 5.2.1, if you
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use <code>libkse</code> (see <code>man libmap.conf</code>).</li>
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<li>For NetBSD, at least version 2.0 is recommended.</li>
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<li>For Linux, a 2.6 kernel is recommended. It is also necessary to
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ensure that your version of <code>glibc</code> has been compiled
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with support for EPoll.</li>
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</ul>
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</div>
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="directive-section"><h2><a name="AsyncRequestWorkerFactor" id="AsyncRequestWorkerFactor">AsyncRequestWorkerFactor</a> <a name="asyncrequestworkerfactor" id="asyncrequestworkerfactor">Directive</a></h2>
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<table class="directive">
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<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Limit concurrent connections per process</td></tr>
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<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>AsyncRequestWorkerFactor <var>factor</var></code></td></tr>
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<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>2</code></td></tr>
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<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
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<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
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<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>event</td></tr>
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<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.3.13 and later</td></tr>
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</table>
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<p>The event MPM handles some connections in an asynchronous way, where
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request worker threads are only allocated for short periods of time as
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needed, and other connections with one request worker thread reserved per
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connection. This can lead to situations where all workers are tied up and
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no worker thread is available to handle new work on established async
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connections.</p>
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<p>To mitigate this problem, the event MPM does two things: Firstly, it
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limits the number of connections accepted per process, depending on the
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number of idle request workers. Secondly, if all workers are busy, it will
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close connections in keep-alive state even if the keep-alive timeout has
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not expired. This allows the respective clients to reconnect to a
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different process which may still have worker threads available.</p>
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<p>This directive can be used to fine-tune the per-process connection
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limit. A process will only accept new connections if the current number of
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connections (not counting connections in the "closing" state) is lower
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than:</p>
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<p class="indent"><strong>
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<code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> +
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(<code class="directive">AsyncRequestWorkerFactor</code> *
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<var>number of idle workers</var>)
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</strong></p>
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<p>This means the absolute maximum numbers of concurrent connections is:</p>
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<p class="indent"><strong>
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(<code class="directive">AsyncRequestWorkerFactor</code> + 1) *
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<code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>
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</strong></p>
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<p><code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> was called
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<code class="directive">MaxClients</code> prior to version 2.3.13. The above value
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shows that the old name did not accurately describe its meaning for the event MPM.</p>
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<p><code class="directive">AsyncRequestWorkerFactor</code> can take non-integer
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arguments, e.g "1.5".</p>
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</div>
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</div>
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<div class="bottomlang">
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<p><span>Available Languages: </span><a href="../en/mod/event.html" title="English"> en </a> |
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<a href="../fr/mod/event.html" hreflang="fr" rel="alternate" title="Fran<61>ais"> fr </a></p>
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</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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<p class="apache">Copyright 2015 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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