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

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 <title>mod_file_cache - Apache HTTP Server</title>
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 <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 2.0</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 2.0</a> &gt; <a href="./">Modules</a></div>
 <div id="page-content">
 <div class="retired"><h4>Please note</h4>
             <p>This document refers to the <strong>2.0</strong> version of Apache httpd, which <strong>is no longer maintained</strong>. Upgrade, and refer to the current version of httpd instead, documented at:</p>
         <ul><li><a href="http://httpd.apache.org/docs/current/">Current release version of Apache HTTP Server documentation</a></li></ul><p>You may follow <a href="http://httpd.apache.org/docs/current/mod/mod_file_cache.html">this link</a> to go to the current version of this document.</p></div><div id="preamble"><h1>Apache Module mod_file_cache</h1>
 <div class="toplang">
 <p><span>Available Languages: </span><a href="../en/mod/mod_file_cache.html" title="English">&nbsp;en&nbsp;</a> |
 <a href="../ko/mod/mod_file_cache.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a></p>
 </div>
 <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Caches a static list of files in memory</td></tr>
 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
 <tr><th><a href="module-dict.html#ModuleIdentifier">Module&#160;Identifier:</a></th><td>file_cache_module</td></tr>
 <tr><th><a href="module-dict.html#SourceFile">Source&#160;File:</a></th><td>mod_file_cache.c</td></tr></table>
 <h3>Summary</h3>


     <div class="warning">
       This module should be used with care. You can easily create a broken
       site using <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code>, so read this document
       carefully.
     </div>

     <p><em>Caching</em> frequently requested files that change very
     infrequently is a technique for reducing server load.
     <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> provides two techniques for caching
     frequently requested <em>static</em> files. Through configuration
     directives, you can direct <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> to either
     open then <code>mmap()</code> a file, or to pre-open a file and save
     the file's open <em>file handle</em>. Both techniques reduce server
     load when processing requests for these files by doing part of the work
     (specifically, the file I/O) for serving the file when the
     server is started rather than during each request.</p>

     <p>Notice: You cannot use this for speeding up CGI programs or
     other files which are served by special content handlers. It
     can only be used for regular files which are usually served by
     the Apache core content handler.</p>

     <p>This module is an extension of and borrows heavily from the
     <code>mod_mmap_static</code> module in Apache 1.3.</p>
 </div>
 <div id="quickview"><h3 class="directives">Directives</h3>
 <ul id="toc">
 <li><img alt="" src="../images/down.gif" /> <a href="#cachefile">CacheFile</a></li>
 <li><img alt="" src="../images/down.gif" /> <a href="#mmapfile">MMapFile</a></li>
 </ul>
 <h3>Topics</h3>
 <ul id="topics">
 <li><img alt="" src="../images/down.gif" /> <a href="#using">Using mod_file_cache</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="using" id="using">Using mod_file_cache</a></h2>

     <p><code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> caches a list of statically
     configured files via <code class="directive"><a href="#mmapfile">MMapFile</a></code> or <code class="directive"><a href="#cachefile">CacheFile</a></code> directives in the main server configuration.</p>

     <p>Not all platforms support both directives. For example, Apache
     on Windows does not currently support the <code class="directive"><a href="#mmapstatic">MMapStatic</a></code> directive, while
     other platforms, like AIX, support both. You will receive an error
     message in the server error log if you attempt to use an
     unsupported directive. If given an unsupported directive, the
     server will start but the file will not be cached. On platforms
     that support both directives, you should experiment with both to
     see which works best for you.</p>

     <h3>MMapFile Directive</h3>

       <p>The <code class="directive"><a href="#mmapfile">MMapFile</a></code>
       directive of <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> maps a list of
       statically configured files into memory through the system call
       <code>mmap()</code>. This system call is available on most modern
       Unix derivates, but not on all. There are sometimes system-specific
       limits on the size and number of files that can be
       <code>mmap()</code>ed, experimentation is probably the easiest way
       to find out.</p>

       <p>This <code>mmap()</code>ing is done once at server start or
       restart, only. So whenever one of the mapped files changes on the
       filesystem you <em>have</em> to restart the server (see the <a href="../stopping.html">Stopping and Restarting</a> documentation).
       To reiterate that point: if the files are modified <em>in place</em>
       without restarting the server you may end up serving requests that
       are completely bogus. You should update files by unlinking the old
       copy and putting a new copy in place. Most tools such as
       <code>rdist</code> and <code>mv</code> do this. The reason why this
       modules doesn't take care of changes to the files is that this check
       would need an extra <code>stat()</code> every time which is a waste
       and against the intent of I/O reduction.</p>


     <h3>CacheFile Directive</h3>

       <p>The <code class="directive"><a href="#cachefile">CacheFile</a></code>
       directive of <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> opens an active
       <em>handle</em> or <em>file descriptor</em> to the file (or files)
       listed in the configuration directive and places these open file
       handles in the cache. When the file is requested, the server
       retrieves the handle from the cache and passes it to the
       <code>sendfile()</code> (or <code>TransmitFile()</code> on Windows),
       socket API.</p>


       <p>This file handle caching is done once at server start or
       restart, only. So whenever one of the cached files changes on
       the filesystem you <em>have</em> to restart the server (see the
       <a href="../stopping.html">Stopping and Restarting</a>
       documentation). To reiterate that point: if the files are
       modified <em>in place</em> without restarting the server you
       may end up serving requests that are completely bogus. You
       should update files by unlinking the old copy and putting a new
       copy in place. Most tools such as <code>rdist</code> and
       <code>mv</code> do this.</p>


     <div class="note"><h3>Note</h3>
       <p>Don't bother asking for a directive which recursively
       caches all the files in a directory. Try this instead... See the
       <code class="directive"><a href="../mod/core.html#include">Include</a></code> directive, and consider
       this command:</p>

       <div class="example"><p><code>
         find /www/htdocs -type f -print \<br />
         | sed -e 's/.*/mmapfile &amp;/' &gt; /www/conf/mmap.conf
       </code></p></div>
     </div>
 </div>
 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 <div class="directive-section"><h2><a name="CacheFile" id="CacheFile">CacheFile</a> <a name="cachefile" id="cachefile">Directive</a></h2>
 <table class="directive">
 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Cache a list of file handles at startup time</td></tr>
 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheFile <var>file-path</var> [<var>file-path</var>] ...</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>Experimental</td></tr>
 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_file_cache</td></tr>
 </table>
     <p>The <code class="directive">CacheFile</code> directive opens handles to
     one or more files (given as whitespace separated arguments) and
     places these handles into the cache at server startup
     time. Handles to cached files are automatically closed on a server
     shutdown.  When the files have changed on the filesystem, the
     server should be restarted to to re-cache them.</p>

     <p>Be careful with the <var>file-path</var> arguments: They have
     to literally match the filesystem path Apache's URL-to-filename
     translation handlers create. We cannot compare inodes or other
     stuff to match paths through symbolic links <em>etc.</em>
     because that again would cost extra <code>stat()</code> system
     calls which is not acceptable. This module may or may not work
     with filenames rewritten by <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> or
     <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.</p>

     <div class="example"><h3>Example</h3><p><code>
       CacheFile /usr/local/apache/htdocs/index.html
     </code></p></div>

 </div>
 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 <div class="directive-section"><h2><a name="MMapFile" id="MMapFile">MMapFile</a> <a name="mmapfile" id="mmapfile">Directive</a></h2>
 <table class="directive">
 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Map a list of files into memory at startup time</td></tr>
 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MMapFile <var>file-path</var> [<var>file-path</var>] ...</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>Experimental</td></tr>
 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_file_cache</td></tr>
 </table>
     <p>The <code class="directive">MMapFile</code> directive maps one or more files
     (given as whitespace separated arguments) into memory at server
     startup time. They are automatically unmapped on a server
     shutdown. When the files have changed on the filesystem at
     least a <code>HUP</code> or <code>USR1</code> signal should be send to
     the server to re-<code>mmap()</code> them.</p>

     <p>Be careful with the <var>file-path</var> arguments: They have
     to literally match the filesystem path Apache's URL-to-filename
     translation handlers create. We cannot compare inodes or other
     stuff to match paths through symbolic links <em>etc.</em>
     because that again would cost extra <code>stat()</code> system
     calls which is not acceptable. This module may or may not work
     with filenames rewritten by <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> or
     <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.</p>

     <div class="example"><h3>Example</h3><p><code>
       MMapFile /usr/local/apache/htdocs/index.html
     </code></p></div>

 </div>
 </div>
 <div class="bottomlang">
 <p><span>Available Languages: </span><a href="../en/mod/mod_file_cache.html" title="English">&nbsp;en&nbsp;</a> |
 <a href="../ko/mod/mod_file_cache.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a></p>
 </div><div id="footer">
 <p class="apache">Copyright 2013 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>
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	<title>mod_file_cache - 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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	<link href="../images/favicon.ico" rel="shortcut icon" /><link href="http://httpd.apache.org/docs/current/mod/mod_file_cache.html" rel="canonical" /></head>
	<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 2.0</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 2.0</a> > <a href="./">Modules</a></div>
	<div id="page-content">
	<div class="retired"><h4>Please note</h4>
	<p>This document refers to the <strong>2.0</strong> version of Apache httpd, which <strong>is no longer maintained</strong>. Upgrade, and refer to the current version of httpd instead, documented at:</p>
	<ul><li><a href="http://httpd.apache.org/docs/current/">Current release version of Apache HTTP Server documentation</a></li></ul><p>You may follow <a href="http://httpd.apache.org/docs/current/mod/mod_file_cache.html">this link</a> to go to the current version of this document.</p></div><div id="preamble"><h1>Apache Module mod_file_cache</h1>
	<div class="toplang">
	<p><span>Available Languages: </span><a href="../en/mod/mod_file_cache.html" title="English"> en </a> \|
	<a href="../ko/mod/mod_file_cache.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
	</div>
	<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Caches a static list of files in memory</td></tr>
	<tr><th><a href="module-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
	<tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>file_cache_module</td></tr>
	<tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_file_cache.c</td></tr></table>
	<h3>Summary</h3>


	<div class="warning">
	This module should be used with care. You can easily create a broken
	site using <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code>, so read this document
	carefully.
	</div>

	<p><em>Caching</em> frequently requested files that change very
	infrequently is a technique for reducing server load.
	<code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> provides two techniques for caching
	frequently requested <em>static</em> files. Through configuration
	directives, you can direct <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> to either
	open then <code>mmap()</code> a file, or to pre-open a file and save
	the file's open <em>file handle</em>. Both techniques reduce server
	load when processing requests for these files by doing part of the work
	(specifically, the file I/O) for serving the file when the
	server is started rather than during each request.</p>

	<p>Notice: You cannot use this for speeding up CGI programs or
	other files which are served by special content handlers. It
	can only be used for regular files which are usually served by
	the Apache core content handler.</p>

	<p>This module is an extension of and borrows heavily from the
	<code>mod_mmap_static</code> module in Apache 1.3.</p>
	</div>
	<div id="quickview"><h3 class="directives">Directives</h3>
	<ul id="toc">
	<li><img alt="" src="../images/down.gif" /> <a href="#cachefile">CacheFile</a></li>
	<li><img alt="" src="../images/down.gif" /> <a href="#mmapfile">MMapFile</a></li>
	</ul>
	<h3>Topics</h3>
	<ul id="topics">
	<li><img alt="" src="../images/down.gif" /> <a href="#using">Using mod_file_cache</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="using" id="using">Using mod_file_cache</a></h2>

	<p><code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> caches a list of statically
	configured files via <code class="directive"><a href="#mmapfile">MMapFile</a></code> or <code class="directive"><a href="#cachefile">CacheFile</a></code> directives in the main server configuration.</p>

	<p>Not all platforms support both directives. For example, Apache
	on Windows does not currently support the <code class="directive"><a href="#mmapstatic">MMapStatic</a></code> directive, while
	other platforms, like AIX, support both. You will receive an error
	message in the server error log if you attempt to use an
	unsupported directive. If given an unsupported directive, the
	server will start but the file will not be cached. On platforms
	that support both directives, you should experiment with both to
	see which works best for you.</p>

	<h3>MMapFile Directive</h3>

	<p>The <code class="directive"><a href="#mmapfile">MMapFile</a></code>
	directive of <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> maps a list of
	statically configured files into memory through the system call
	<code>mmap()</code>. This system call is available on most modern
	Unix derivates, but not on all. There are sometimes system-specific
	limits on the size and number of files that can be
	<code>mmap()</code>ed, experimentation is probably the easiest way
	to find out.</p>

	<p>This <code>mmap()</code>ing is done once at server start or
	restart, only. So whenever one of the mapped files changes on the
	filesystem you <em>have</em> to restart the server (see the <a href="../stopping.html">Stopping and Restarting</a> documentation).
	To reiterate that point: if the files are modified <em>in place</em>
	without restarting the server you may end up serving requests that
	are completely bogus. You should update files by unlinking the old
	copy and putting a new copy in place. Most tools such as
	<code>rdist</code> and <code>mv</code> do this. The reason why this
	modules doesn't take care of changes to the files is that this check
	would need an extra <code>stat()</code> every time which is a waste
	and against the intent of I/O reduction.</p>


	<h3>CacheFile Directive</h3>

	<p>The <code class="directive"><a href="#cachefile">CacheFile</a></code>
	directive of <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> opens an active
	<em>handle</em> or <em>file descriptor</em> to the file (or files)
	listed in the configuration directive and places these open file
	handles in the cache. When the file is requested, the server
	retrieves the handle from the cache and passes it to the
	<code>sendfile()</code> (or <code>TransmitFile()</code> on Windows),
	socket API.</p>



	<p>This file handle caching is done once at server start or
	restart, only. So whenever one of the cached files changes on
	the filesystem you <em>have</em> to restart the server (see the
	<a href="../stopping.html">Stopping and Restarting</a>
	documentation). To reiterate that point: if the files are
	modified <em>in place</em> without restarting the server you
	may end up serving requests that are completely bogus. You
	should update files by unlinking the old copy and putting a new
	copy in place. Most tools such as <code>rdist</code> and
	<code>mv</code> do this.</p>


	<div class="note"><h3>Note</h3>
	<p>Don't bother asking for a directive which recursively
	caches all the files in a directory. Try this instead... See the
	<code class="directive"><a href="../mod/core.html#include">Include</a></code> directive, and consider
	this command:</p>

	<div class="example"><p><code>
	find /www/htdocs -type f -print \<br />
	\| sed -e 's/.*/mmapfile &/' > /www/conf/mmap.conf
	</code></p></div>
	</div>
	</div>
	<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
	<div class="directive-section"><h2><a name="CacheFile" id="CacheFile">CacheFile</a> <a name="cachefile" id="cachefile">Directive</a></h2>
	<table class="directive">
	<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Cache a list of file handles at startup time</td></tr>
	<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheFile <var>file-path</var> [<var>file-path</var>] ...</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>Experimental</td></tr>
	<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_file_cache</td></tr>
	</table>
	<p>The <code class="directive">CacheFile</code> directive opens handles to
	one or more files (given as whitespace separated arguments) and
	places these handles into the cache at server startup
	time. Handles to cached files are automatically closed on a server
	shutdown. When the files have changed on the filesystem, the
	server should be restarted to to re-cache them.</p>

	<p>Be careful with the <var>file-path</var> arguments: They have
	to literally match the filesystem path Apache's URL-to-filename
	translation handlers create. We cannot compare inodes or other
	stuff to match paths through symbolic links <em>etc.</em>
	because that again would cost extra <code>stat()</code> system
	calls which is not acceptable. This module may or may not work
	with filenames rewritten by <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> or
	<code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.</p>

	<div class="example"><h3>Example</h3><p><code>
	CacheFile /usr/local/apache/htdocs/index.html
	</code></p></div>

	</div>
	<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
	<div class="directive-section"><h2><a name="MMapFile" id="MMapFile">MMapFile</a> <a name="mmapfile" id="mmapfile">Directive</a></h2>
	<table class="directive">
	<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Map a list of files into memory at startup time</td></tr>
	<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>MMapFile <var>file-path</var> [<var>file-path</var>] ...</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>Experimental</td></tr>
	<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_file_cache</td></tr>
	</table>
	<p>The <code class="directive">MMapFile</code> directive maps one or more files
	(given as whitespace separated arguments) into memory at server
	startup time. They are automatically unmapped on a server
	shutdown. When the files have changed on the filesystem at
	least a <code>HUP</code> or <code>USR1</code> signal should be send to
	the server to re-<code>mmap()</code> them.</p>

	<p>Be careful with the <var>file-path</var> arguments: They have
	to literally match the filesystem path Apache's URL-to-filename
	translation handlers create. We cannot compare inodes or other
	stuff to match paths through symbolic links <em>etc.</em>
	because that again would cost extra <code>stat()</code> system
	calls which is not acceptable. This module may or may not work
	with filenames rewritten by <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> or
	<code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.</p>

	<div class="example"><h3>Example</h3><p><code>
	MMapFile /usr/local/apache/htdocs/index.html
	</code></p></div>

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