apache/docs/manual/mod/mod_file_cache.html.en

   1 <?xml version="1.0" encoding="ISO-8859-1"?>
   2 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
   3 <html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!--
   4         XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
   5               This file is generated from xml source: DO NOT EDIT
   6         XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
   7       -->
   8 <title>mod_file_cache - Apache HTTP Server</title>
   9 <link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
  10 <link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" />
  11 <link href="../style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" />
  12 <link href="../images/favicon.ico" rel="shortcut icon" /></head>
  13 <body>
  14 <div id="page-header">
  15 <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>
  16 <p class="apache">Apache HTTP Server Version 2.3</p>
  17 <img alt="" src="../images/feather.gif" /></div>
  18 <div class="up"><a href="./"><img title="&lt;-" alt="&lt;-" src="../images/left.gif" /></a></div>
  19 <div id="path">
  20 <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 2.3</a> &gt; <a href="./">Modules</a></div>
  21 <div id="page-content">
  22 <div id="preamble"><h1>Apache Module mod_file_cache</h1>
  23 <div class="toplang">
  24 <p><span>Available Languages: </span><a href="../en/mod/mod_file_cache.html" title="English">&nbsp;en&nbsp;</a> |
  25 <a href="../ko/mod/mod_file_cache.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a></p>
  26 </div>
  27 <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>
  28 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
  29 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>file_cache_module</td></tr>
  30 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_file_cache.c</td></tr></table>
  31 <h3>Summary</h3>
  32
  33
  34     <div class="warning">
  35       This module should be used with care. You can easily create a broken
  36       site using <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code>, so read this document
  37       carefully.
  38     </div>
  39
  40     <p><em>Caching</em> frequently requested files that change very
  41     infrequently is a technique for reducing server load.
  42     <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> provides two techniques for caching
  43     frequently requested <em>static</em> files. Through configuration
  44     directives, you can direct <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> to either
  45     open then <code>mmap()</code> a file, or to pre-open a file and save
  46     the file's open <em>file handle</em>. Both techniques reduce server
  47     load when processing requests for these files by doing part of the work
  48     (specifically, the file I/O) for serving the file when the
  49     server is started rather than during each request.</p>
  50
  51     <p>Notice: You cannot use this for speeding up CGI programs or
  52     other files which are served by special content handlers. It
  53     can only be used for regular files which are usually served by
  54     the Apache core content handler.</p>
  55
  56     <p>This module is an extension of and borrows heavily from the
  57     <code>mod_mmap_static</code> module in Apache 1.3.</p>
  58 </div>
  59 <div id="quickview"><h3 class="directives">Directives</h3>
  60 <ul id="toc">
  61 <li><img alt="" src="../images/down.gif" /> <a href="#cachefile">CacheFile</a></li>
  62 <li><img alt="" src="../images/down.gif" /> <a href="#mmapfile">MMapFile</a></li>
  63 </ul>
  64 <h3>Topics</h3>
  65 <ul id="topics">
  66 <li><img alt="" src="../images/down.gif" /> <a href="#using">Using mod_file_cache</a></li>
  67 </ul></div>
  68 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
  69 <div class="section">
  70 <h2><a name="using" id="using">Using mod_file_cache</a></h2>
  71
  72     <p><code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> caches a list of statically
  73     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>
  74
  75     <p>Not all platforms support both directives. You will receive an error
  76     message in the server error log if you attempt to use an
  77     unsupported directive. If given an unsupported directive, the
  78     server will start but the file will not be cached. On platforms
  79     that support both directives, you should experiment with both to
  80     see which works best for you.</p>
  81
  82     <h3>MMapFile Directive</h3>
  83
  84       <p>The <code class="directive"><a href="#mmapfile">MMapFile</a></code>
  85       directive of <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> maps a list of
  86       statically configured files into memory through the system call
  87       <code>mmap()</code>. This system call is available on most modern
  88       Unix derivates, but not on all. There are sometimes system-specific
  89       limits on the size and number of files that can be
  90       <code>mmap()</code>ed, experimentation is probably the easiest way
  91       to find out.</p>
  92
  93       <p>This <code>mmap()</code>ing is done once at server start or
  94       restart, only. So whenever one of the mapped files changes on the
  95       filesystem you <em>have</em> to restart the server (see the <a href="../stopping.html">Stopping and Restarting</a> documentation).
  96       To reiterate that point: if the files are modified <em>in place</em>
  97       without restarting the server you may end up serving requests that
  98       are completely bogus. You should update files by unlinking the old
  99       copy and putting a new copy in place. Most tools such as
 100       <code>rdist</code> and <code>mv</code> do this. The reason why this
 101       modules doesn't take care of changes to the files is that this check
 102       would need an extra <code>stat()</code> every time which is a waste
 103       and against the intent of I/O reduction.</p>
 104
 105
 106     <h3>CacheFile Directive</h3>
 107
 108       <p>The <code class="directive"><a href="#cachefile">CacheFile</a></code>
 109       directive of <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> opens an active
 110       <em>handle</em> or <em>file descriptor</em> to the file (or files)
 111       listed in the configuration directive and places these open file
 112       handles in the cache. When the file is requested, the server
 113       retrieves the handle from the cache and passes it to the
 114       <code>sendfile()</code> (or <code>TransmitFile()</code> on Windows),
 115       socket API.</p>
 116
 117
 118
 119       <p>This file handle caching is done once at server start or
 120       restart, only. So whenever one of the cached files changes on
 121       the filesystem you <em>have</em> to restart the server (see the
 122       <a href="../stopping.html">Stopping and Restarting</a>
 123       documentation). To reiterate that point: if the files are
 124       modified <em>in place</em> without restarting the server you
 125       may end up serving requests that are completely bogus. You
 126       should update files by unlinking the old copy and putting a new
 127       copy in place. Most tools such as <code>rdist</code> and
 128       <code>mv</code> do this.</p>
 129
 130
 131     <div class="note"><h3>Note</h3>
 132       <p>Don't bother asking for a directive which recursively
 133       caches all the files in a directory. Try this instead... See the
 134       <code class="directive"><a href="../mod/core.html#include">Include</a></code> directive, and consider
 135       this command:</p>
 136
 137       <div class="example"><p><code>
 138         find /www/htdocs -type f -print \<br />
 139         | sed -e 's/.*/mmapfile &amp;/' &gt; /www/conf/mmap.conf
 140       </code></p></div>
 141     </div>
 142 </div>
 143 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 144 <div class="directive-section"><h2><a name="CacheFile" id="CacheFile">CacheFile</a> <a name="cachefile" id="cachefile">Directive</a></h2>
 145 <table class="directive">
 146 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Cache a list of file handles at startup time</td></tr>
 147 <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>
 148 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 149 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
 150 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_file_cache</td></tr>
 151 </table>
 152     <p>The <code class="directive">CacheFile</code> directive opens handles to
 153     one or more files (given as whitespace separated arguments) and
 154     places these handles into the cache at server startup
 155     time. Handles to cached files are automatically closed on a server
 156     shutdown.  When the files have changed on the filesystem, the
 157     server should be restarted to re-cache them.</p>
 158
 159     <p>Be careful with the <var>file-path</var> arguments: They have
 160     to literally match the filesystem path Apache's URL-to-filename
 161     translation handlers create. We cannot compare inodes or other
 162     stuff to match paths through symbolic links <em>etc.</em>
 163     because that again would cost extra <code>stat()</code> system
 164     calls which is not acceptable. This module may or may not work
 165     with filenames rewritten by <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> or
 166     <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.</p>
 167
 168     <div class="example"><h3>Example</h3><p><code>
 169       CacheFile /usr/local/apache/htdocs/index.html
 170     </code></p></div>
 171
 172 </div>
 173 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 174 <div class="directive-section"><h2><a name="MMapFile" id="MMapFile">MMapFile</a> <a name="mmapfile" id="mmapfile">Directive</a></h2>
 175 <table class="directive">
 176 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Map a list of files into memory at startup time</td></tr>
 177 <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>
 178 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
 179 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
 180 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_file_cache</td></tr>
 181 </table>
 182     <p>The <code class="directive">MMapFile</code> directive maps one or more files
 183     (given as whitespace separated arguments) into memory at server
 184     startup time. They are automatically unmapped on a server
 185     shutdown. When the files have changed on the filesystem at
 186     least a <code>HUP</code> or <code>USR1</code> signal should be send to
 187     the server to re-<code>mmap()</code> them.</p>
 188
 189     <p>Be careful with the <var>file-path</var> arguments: They have
 190     to literally match the filesystem path Apache's URL-to-filename
 191     translation handlers create. We cannot compare inodes or other
 192     stuff to match paths through symbolic links <em>etc.</em>
 193     because that again would cost extra <code>stat()</code> system
 194     calls which is not acceptable. This module may or may not work
 195     with filenames rewritten by <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> or
 196     <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.</p>
 197
 198     <div class="example"><h3>Example</h3><p><code>
 199       MMapFile /usr/local/apache/htdocs/index.html
 200     </code></p></div>
 201
 202 </div>
 203 </div>
 204 <div class="bottomlang">
 205 <p><span>Available Languages: </span><a href="../en/mod/mod_file_cache.html" title="English">&nbsp;en&nbsp;</a> |
 206 <a href="../ko/mod/mod_file_cache.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a></p>
 207 </div><div id="footer">
 208 <p class="apache">Copyright 2009 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>
 209 <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>
 210 </body></html>