docs/manual/mod/event.html.en - httpd - Git at Google

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 <title>event - Apache HTTP Server</title>
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 <p class="apache">Apache HTTP Server Version 2.5</p>
 <img alt="" src="../images/feather.gif" /></div>
 <div class="up"><a href="./"><img title="&lt;-" alt="&lt;-" src="../images/left.gif" /></a></div>
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 <a href="http://www.apache.org/">Apache</a> &gt; <a href="http://httpd.apache.org/">HTTP Server</a> &gt; <a href="http://httpd.apache.org/docs/">Documentation</a> &gt; <a href="../">Version 2.5</a> &gt; <a href="./">Modules</a></div>
 <div id="page-content">
 <div id="preamble"><h1>Apache MPM event</h1>
 <div class="toplang">
 <p><span>Available Languages: </span><a href="../en/mod/event.html" title="English">&nbsp;en&nbsp;</a> |
 <a href="../fr/mod/event.html" hreflang="fr" rel="alternate" title="Français">&nbsp;fr&nbsp;</a></p>
 </div>
 <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
 of consuming threads only for connections with active processing</td></tr>
 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>mpm_event_module</td></tr>
 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>event.c</td></tr></table>
 <h3>Summary</h3>

     <p>The <code class="module"><a href="../mod/event.html">event</a></code> Multi-Processing Module (MPM) is
     designed to allow more requests to be served simultaneously by
     passing off some processing work to supporting threads, freeing up
     the main threads to work on new requests.  It is based on the
     <code class="module"><a href="../mod/worker.html">worker</a></code> MPM, which implements a hybrid
     multi-process multi-threaded server.  Run-time configuration
     directives are identical to those provided by
     <code class="module"><a href="../mod/worker.html">worker</a></code>.</p>

     <p>To use the <code class="module"><a href="../mod/event.html">event</a></code> MPM, add
       <code>--with-mpm=event</code> to the <code class="program"><a href="../programs/configure.html">configure</a></code>
       script's arguments when building the <code class="program"><a href="../programs/httpd.html">httpd</a></code>.</p>

 </div>
 <div id="quickview"><h3 class="directives">Directives</h3>
 <ul id="toc">
 <li><img alt="" src="../images/down.gif" /> <a href="#asyncrequestworkerfactor">AsyncRequestWorkerFactor</a></li>
 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li>
 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#enableexceptionhook">EnableExceptionHook</a></li>
 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#group">Group</a></li>
 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li>
 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li>
 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</a></li>
 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li>
 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></li>
 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxsparethreads">MaxSpareThreads</a></li>
 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#minsparethreads">MinSpareThreads</a></li>
 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li>
 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li>
 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li>
 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li>
 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadlimit">ThreadLimit</a></li>
 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadsperchild">ThreadsPerChild</a></li>
 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadstacksize">ThreadStackSize</a></li>
 <li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#user">User</a></li>
 </ul>
 <h3>Topics</h3>
 <ul id="topics">
 <li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
 <li><img alt="" src="../images/down.gif" /> <a href="#requirements">Requirements</a></li>
 </ul><h3>See also</h3>
 <ul class="seealso">
 <li><a href="worker.html">The worker MPM</a></li>
 </ul></div>
 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 <div class="section">
 <h2><a name="how-it-works" id="how-it-works">How it Works</a></h2>
     <p>This MPM tries to fix the 'keep alive problem' in HTTP. After a client
     completes the first request, the client can keep the connection
     open, and send further requests using the same socket. This can
     save signifigant overhead in creating TCP connections. However,
     Apache HTTP Server traditionally keeps an entire child process/thread waiting
     for data from the client, which brings its own disadvantages. To
     solve this problem, this MPM uses a dedicated thread to handle both
     the Listening sockets, all sockets that are in a Keep Alive state,
     and sockets where the handler and protocol filters have done their work
     and the only remaining thing to do is send the data to the client. The
     status page of <code class="module"><a href="../mod/mod_status.html">mod_status</a></code> shows how many connections are
     in the mentioned states.</p>

     <p>The improved connection handling does not yet work for certain
     connection filters, in particular SSL. For SSL connections, this MPM will
     fall back to the behaviour of the <code class="module"><a href="../mod/worker.html">worker</a></code> MPM and
     reserve one worker thread per connection.</p>

     <p>The MPM assumes that the underlying <code>apr_pollset</code>
     implementation is reasonably threadsafe. This enables the MPM to
     avoid excessive high level locking, or having to wake up the listener
     thread in order to send it a keep-alive socket. This is currently
     only compatible with KQueue and EPoll.</p>

 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 <div class="section">
 <h2><a name="requirements" id="requirements">Requirements</a></h2>
     <p>This MPM depends on <a class="glossarylink" href="../glossary.html#apr" title="see glossary">APR</a>'s atomic
     compare-and-swap operations for thread synchronization. If you are
     compiling for an x86 target and you don't need to support 386s, or
     you are compiling for a SPARC and you don't need to run on
     pre-UltraSPARC chips, add
     <code>--enable-nonportable-atomics=yes</code> to the
     <code class="program"><a href="../programs/configure.html">configure</a></code> script's arguments. This will cause
     APR to implement atomic operations using efficient opcodes not
     available in older CPUs.</p>

     <p>This MPM does not perform well on older platforms which lack good
     threading, but the requirement for EPoll or KQueue makes this
     moot.</p>

     <ul>

       <li>To use this MPM on FreeBSD, FreeBSD 5.3 or higher is recommended.
       However, it is possible to run this MPM on FreeBSD 5.2.1, if you
       use <code>libkse</code> (see <code>man libmap.conf</code>).</li>

       <li>For NetBSD, at least version 2.0 is recommended.</li>

       <li>For Linux, a 2.6 kernel is recommended. It is also necessary to
       ensure that your version of <code>glibc</code> has been compiled
       with support for EPoll.</li>

     </ul>
 </div>
 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 <div class="directive-section"><h2><a name="AsyncRequestWorkerFactor" id="AsyncRequestWorkerFactor">AsyncRequestWorkerFactor</a> <a name="asyncrequestworkerfactor" id="asyncrequestworkerfactor">Directive</a></h2>
 <table class="directive">
 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Limit concurrent connections per process</td></tr>
 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>AsyncRequestWorkerFactor <var>factor</var></code></td></tr>
 <tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>2</code></td></tr>
 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>event</td></tr>
 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.3.13 and later</td></tr>
 </table>
     <p>The event MPM handles some connections in an asynchronous way, where
     request worker threads are only allocated for short periods of time as
     needed, and other (mostly SSL) connections with one request worker thread
     reserved per connection. This can lead to situations where all workers are
     tied up and no worker thread is available to handle new work on established
     async connetions.</p>

     <p>To mitigate this problem, the event MPM does two things: Firstly, it
     limits the number of connections accepted per process, depending on the
     number of idle request workers. Secondly, if all workers are busy, it will
     close connections in keep-alive state even if the keep-alive timeout has
     not expired. This allows the respective clients to reconnect to a
     different process which may still have worker threads available.</p>

     <p>This directive can be used to fine-tune the per-process connection
     limit. A process will only accept new connections if the current number of
     connections is lower than:</p>

     <p class="indent"><strong>
         <code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> +
         (<code class="directive">AsyncRequestWorkerFactor</code> *
         <var>number of idle workers</var>)
     </strong></p>

     <p>This means the absolute maximum numbers of concurrent connections is:</p>

     <p class="indent"><strong>
         (<code class="directive">AsyncRequestWorkerFactor</code> + 1) *
         <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>
     </strong></p>

     <p><code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> was called
     <code class="directive">MaxClients</code> prior to version 2.3.13. The above value
     shows that the old name did not accurately describe its meaning for the event MPM.</p>

     <p><code class="directive">AsyncRequestWorkerFactor</code> can take non-integer
     arguments, e.g "1.5".</p>


 </div>
 </div>
 <div class="bottomlang">
 <p><span>Available Languages: </span><a href="../en/mod/event.html" title="English">&nbsp;en&nbsp;</a> |
 <a href="../fr/mod/event.html" hreflang="fr" rel="alternate" title="Français">&nbsp;fr&nbsp;</a></p>
 </div><div id="footer">
 <p class="apache">Copyright 2012 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>
 <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>
 </body></html>
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	<title>event - Apache HTTP Server</title>
	<link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
	<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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	<body>
	<div id="page-header">
	<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>
	<p class="apache">Apache HTTP Server Version 2.5</p>
	<img alt="" src="../images/feather.gif" /></div>
	<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
	<div id="path">
	<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>
	<div id="page-content">
	<div id="preamble"><h1>Apache MPM event</h1>
	<div class="toplang">
	<p><span>Available Languages: </span><a href="../en/mod/event.html" title="English"> en </a> \|
	<a href="../fr/mod/event.html" hreflang="fr" rel="alternate" title="Français"> fr </a></p>
	</div>
	<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
	of consuming threads only for connections with active processing</td></tr>
	<tr><th><a href="module-dict.html#Status">Status:</a></th><td>MPM</td></tr>
	<tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>mpm_event_module</td></tr>
	<tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>event.c</td></tr></table>
	<h3>Summary</h3>

	<p>The <code class="module"><a href="../mod/event.html">event</a></code> Multi-Processing Module (MPM) is
	designed to allow more requests to be served simultaneously by
	passing off some processing work to supporting threads, freeing up
	the main threads to work on new requests. It is based on the
	<code class="module"><a href="../mod/worker.html">worker</a></code> MPM, which implements a hybrid
	multi-process multi-threaded server. Run-time configuration
	directives are identical to those provided by
	<code class="module"><a href="../mod/worker.html">worker</a></code>.</p>

	<p>To use the <code class="module"><a href="../mod/event.html">event</a></code> MPM, add
	<code>--with-mpm=event</code> to the <code class="program"><a href="../programs/configure.html">configure</a></code>
	script's arguments when building the <code class="program"><a href="../programs/httpd.html">httpd</a></code>.</p>

	</div>
	<div id="quickview"><h3 class="directives">Directives</h3>
	<ul id="toc">
	<li><img alt="" src="../images/down.gif" /> <a href="#asyncrequestworkerfactor">AsyncRequestWorkerFactor</a></li>
	<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#coredumpdirectory">CoreDumpDirectory</a></li>
	<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#enableexceptionhook">EnableExceptionHook</a></li>
	<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#group">Group</a></li>
	<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listen">Listen</a></li>
	<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#listenbacklog">ListenBacklog</a></li>
	<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxconnectionsperchild">MaxConnectionsPerChild</a></li>
	<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxmemfree">MaxMemFree</a></li>
	<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></li>
	<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#maxsparethreads">MaxSpareThreads</a></li>
	<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#minsparethreads">MinSpareThreads</a></li>
	<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#pidfile">PidFile</a></li>
	<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#scoreboardfile">ScoreBoardFile</a></li>
	<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#sendbuffersize">SendBufferSize</a></li>
	<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#serverlimit">ServerLimit</a></li>
	<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#startservers">StartServers</a></li>
	<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadlimit">ThreadLimit</a></li>
	<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadsperchild">ThreadsPerChild</a></li>
	<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#threadstacksize">ThreadStackSize</a></li>
	<li><img alt="" src="../images/right.gif" /> <a href="mpm_common.html#user">User</a></li>
	</ul>
	<h3>Topics</h3>
	<ul id="topics">
	<li><img alt="" src="../images/down.gif" /> <a href="#how-it-works">How it Works</a></li>
	<li><img alt="" src="../images/down.gif" /> <a href="#requirements">Requirements</a></li>
	</ul><h3>See also</h3>
	<ul class="seealso">
	<li><a href="worker.html">The worker MPM</a></li>
	</ul></div>
	<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
	<div class="section">
	<h2><a name="how-it-works" id="how-it-works">How it Works</a></h2>
	<p>This MPM tries to fix the 'keep alive problem' in HTTP. After a client
	completes the first request, the client can keep the connection
	open, and send further requests using the same socket. This can
	save signifigant overhead in creating TCP connections. However,
	Apache HTTP Server traditionally keeps an entire child process/thread waiting
	for data from the client, which brings its own disadvantages. To
	solve this problem, this MPM uses a dedicated thread to handle both
	the Listening sockets, all sockets that are in a Keep Alive state,
	and sockets where the handler and protocol filters have done their work
	and the only remaining thing to do is send the data to the client. The
	status page of <code class="module"><a href="../mod/mod_status.html">mod_status</a></code> shows how many connections are
	in the mentioned states.</p>

	<p>The improved connection handling does not yet work for certain
	connection filters, in particular SSL. For SSL connections, this MPM will
	fall back to the behaviour of the <code class="module"><a href="../mod/worker.html">worker</a></code> MPM and
	reserve one worker thread per connection.</p>

	<p>The MPM assumes that the underlying <code>apr_pollset</code>
	implementation is reasonably threadsafe. This enables the MPM to
	avoid excessive high level locking, or having to wake up the listener
	thread in order to send it a keep-alive socket. This is currently
	only compatible with KQueue and EPoll.</p>

	</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
	<div class="section">
	<h2><a name="requirements" id="requirements">Requirements</a></h2>
	<p>This MPM depends on <a class="glossarylink" href="../glossary.html#apr" title="see glossary">APR</a>'s atomic
	compare-and-swap operations for thread synchronization. If you are
	compiling for an x86 target and you don't need to support 386s, or
	you are compiling for a SPARC and you don't need to run on
	pre-UltraSPARC chips, add
	<code>--enable-nonportable-atomics=yes</code> to the
	<code class="program"><a href="../programs/configure.html">configure</a></code> script's arguments. This will cause
	APR to implement atomic operations using efficient opcodes not
	available in older CPUs.</p>

	<p>This MPM does not perform well on older platforms which lack good
	threading, but the requirement for EPoll or KQueue makes this
	moot.</p>

	<ul>

	<li>To use this MPM on FreeBSD, FreeBSD 5.3 or higher is recommended.
	However, it is possible to run this MPM on FreeBSD 5.2.1, if you
	use <code>libkse</code> (see <code>man libmap.conf</code>).</li>

	<li>For NetBSD, at least version 2.0 is recommended.</li>

	<li>For Linux, a 2.6 kernel is recommended. It is also necessary to
	ensure that your version of <code>glibc</code> has been compiled
	with support for EPoll.</li>

	</ul>
	</div>
	<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
	<div class="directive-section"><h2><a name="AsyncRequestWorkerFactor" id="AsyncRequestWorkerFactor">AsyncRequestWorkerFactor</a> <a name="asyncrequestworkerfactor" id="asyncrequestworkerfactor">Directive</a></h2>
	<table class="directive">
	<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Limit concurrent connections per process</td></tr>
	<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>AsyncRequestWorkerFactor <var>factor</var></code></td></tr>
	<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>2</code></td></tr>
	<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
	<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>MPM</td></tr>
	<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>event</td></tr>
	<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.3.13 and later</td></tr>
	</table>
	<p>The event MPM handles some connections in an asynchronous way, where
	request worker threads are only allocated for short periods of time as
	needed, and other (mostly SSL) connections with one request worker thread
	reserved per connection. This can lead to situations where all workers are
	tied up and no worker thread is available to handle new work on established
	async connetions.</p>

	<p>To mitigate this problem, the event MPM does two things: Firstly, it
	limits the number of connections accepted per process, depending on the
	number of idle request workers. Secondly, if all workers are busy, it will
	close connections in keep-alive state even if the keep-alive timeout has
	not expired. This allows the respective clients to reconnect to a
	different process which may still have worker threads available.</p>

	<p>This directive can be used to fine-tune the per-process connection
	limit. A process will only accept new connections if the current number of
	connections is lower than:</p>

	<p class="indent"><strong>
	<code class="directive"><a href="../mod/mpm_common.html#threadsperchild">ThreadsPerChild</a></code> +
	(<code class="directive">AsyncRequestWorkerFactor</code> *
	<var>number of idle workers</var>)
	</strong></p>

	<p>This means the absolute maximum numbers of concurrent connections is:</p>

	<p class="indent"><strong>
	(<code class="directive">AsyncRequestWorkerFactor</code> + 1) *
	<code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code>
	</strong></p>

	<p><code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> was called
	<code class="directive">MaxClients</code> prior to version 2.3.13. The above value
	shows that the old name did not accurately describe its meaning for the event MPM.</p>

	<p><code class="directive">AsyncRequestWorkerFactor</code> can take non-integer
	arguments, e.g "1.5".</p>


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