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19 <p class="apache">Apache HTTP Server Version 2.5</p>
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24 <div id="page-content">
25 <div id="preamble"><h1>Apache Module mod_file_cache</h1>
27 <p><span>Available Languages: </span><a href="../en/mod/mod_file_cache.html" title="English"> en </a> |
28 <a href="../ko/mod/mod_file_cache.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
30 <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>
31 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
32 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>file_cache_module</td></tr>
33 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_file_cache.c</td></tr></table>
38 This module should be used with care. You can easily create a broken
39 site using <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code>, so read this document
43 <p><em>Caching</em> frequently requested files that change very
44 infrequently is a technique for reducing server load.
45 <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> provides two techniques for caching
46 frequently requested <em>static</em> files. Through configuration
47 directives, you can direct <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> to either
48 open then <code>mmap()</code> a file, or to pre-open a file and save
49 the file's open <em>file handle</em>. Both techniques reduce server
50 load when processing requests for these files by doing part of the work
51 (specifically, the file I/O) for serving the file when the
52 server is started rather than during each request.</p>
54 <p>Notice: You cannot use this for speeding up CGI programs or
55 other files which are served by special content handlers. It
56 can only be used for regular files which are usually served by
57 the Apache core content handler.</p>
59 <p>This module is an extension of and borrows heavily from the
60 <code>mod_mmap_static</code> module in Apache 1.3.</p>
62 <div id="quickview"><h3 class="directives">Directives</h3>
64 <li><img alt="" src="../images/down.gif" /> <a href="#cachefile">CacheFile</a></li>
65 <li><img alt="" src="../images/down.gif" /> <a href="#mmapfile">MMapFile</a></li>
69 <li><img alt="" src="../images/down.gif" /> <a href="#using">Using mod_file_cache</a></li>
71 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
73 <h2><a name="using" id="using">Using mod_file_cache</a></h2>
75 <p><code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> caches a list of statically
76 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>
78 <p>Not all platforms support both directives. You will receive an error
79 message in the server error log if you attempt to use an
80 unsupported directive. If given an unsupported directive, the
81 server will start but the file will not be cached. On platforms
82 that support both directives, you should experiment with both to
83 see which works best for you.</p>
85 <h3>MMapFile Directive</h3>
87 <p>The <code class="directive"><a href="#mmapfile">MMapFile</a></code>
88 directive of <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> maps a list of
89 statically configured files into memory through the system call
90 <code>mmap()</code>. This system call is available on most modern
91 Unix derivatives, but not on all. There are sometimes system-specific
92 limits on the size and number of files that can be
93 <code>mmap()</code>ed, experimentation is probably the easiest way
96 <p>This <code>mmap()</code>ing is done once at server start or
97 restart, only. So whenever one of the mapped files changes on the
98 filesystem you <em>have</em> to restart the server (see the <a href="../stopping.html">Stopping and Restarting</a> documentation).
99 To reiterate that point: if the files are modified <em>in place</em>
100 without restarting the server you may end up serving requests that
101 are completely bogus. You should update files by unlinking the old
102 copy and putting a new copy in place. Most tools such as
103 <code>rdist</code> and <code>mv</code> do this. The reason why this
104 modules doesn't take care of changes to the files is that this check
105 would need an extra <code>stat()</code> every time which is a waste
106 and against the intent of I/O reduction.</p>
109 <h3>CacheFile Directive</h3>
111 <p>The <code class="directive"><a href="#cachefile">CacheFile</a></code>
112 directive of <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> opens an active
113 <em>handle</em> or <em>file descriptor</em> to the file (or files)
114 listed in the configuration directive and places these open file
115 handles in the cache. When the file is requested, the server
116 retrieves the handle from the cache and passes it to the
117 <code>sendfile()</code> (or <code>TransmitFile()</code> on Windows),
122 <p>This file handle caching is done once at server start or
123 restart, only. So whenever one of the cached files changes on
124 the filesystem you <em>have</em> to restart the server (see the
125 <a href="../stopping.html">Stopping and Restarting</a>
126 documentation). To reiterate that point: if the files are
127 modified <em>in place</em> without restarting the server you
128 may end up serving requests that are completely bogus. You
129 should update files by unlinking the old copy and putting a new
130 copy in place. Most tools such as <code>rdist</code> and
131 <code>mv</code> do this.</p>
134 <div class="note"><h3>Note</h3>
135 <p>Don't bother asking for a directive which recursively
136 caches all the files in a directory. Try this instead... See the
137 <code class="directive"><a href="../mod/core.html#include">Include</a></code> directive, and consider
140 <div class="example"><p><code>
141 find /www/htdocs -type f -print \<br />
142 | sed -e 's/.*/mmapfile &/' > /www/conf/mmap.conf
146 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
147 <div class="directive-section"><h2><a name="CacheFile" id="CacheFile">CacheFile</a> <a name="cachefile" id="cachefile">Directive</a></h2>
148 <table class="directive">
149 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Cache a list of file handles at startup time</td></tr>
150 <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>
151 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
152 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
153 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_file_cache</td></tr>
155 <p>The <code class="directive">CacheFile</code> directive opens handles to
156 one or more files (given as whitespace separated arguments) and
157 places these handles into the cache at server startup
158 time. Handles to cached files are automatically closed on a server
159 shutdown. When the files have changed on the filesystem, the
160 server should be restarted to re-cache them.</p>
162 <p>Be careful with the <var>file-path</var> arguments: They have
163 to literally match the filesystem path Apache's URL-to-filename
164 translation handlers create. We cannot compare inodes or other
165 stuff to match paths through symbolic links <em>etc.</em>
166 because that again would cost extra <code>stat()</code> system
167 calls which is not acceptable. This module may or may not work
168 with filenames rewritten by <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> or
169 <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.</p>
171 <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">
172 CacheFile /usr/local/apache/htdocs/index.html
177 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
178 <div class="directive-section"><h2><a name="MMapFile" id="MMapFile">MMapFile</a> <a name="mmapfile" id="mmapfile">Directive</a></h2>
179 <table class="directive">
180 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Map a list of files into memory at startup time</td></tr>
181 <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>
182 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
183 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
184 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_file_cache</td></tr>
186 <p>The <code class="directive">MMapFile</code> directive maps one or more files
187 (given as whitespace separated arguments) into memory at server
188 startup time. They are automatically unmapped on a server
189 shutdown. When the files have changed on the filesystem at
190 least a <code>HUP</code> or <code>USR1</code> signal should be send to
191 the server to re-<code>mmap()</code> them.</p>
193 <p>Be careful with the <var>file-path</var> arguments: They have
194 to literally match the filesystem path Apache's URL-to-filename
195 translation handlers create. We cannot compare inodes or other
196 stuff to match paths through symbolic links <em>etc.</em>
197 because that again would cost extra <code>stat()</code> system
198 calls which is not acceptable. This module may or may not work
199 with filenames rewritten by <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> or
200 <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.</p>
202 <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">
203 MMapFile /usr/local/apache/htdocs/index.html
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210 <p><span>Available Languages: </span><a href="../en/mod/mod_file_cache.html" title="English"> en </a> |
211 <a href="../ko/mod/mod_file_cache.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
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213 <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>
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