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16 <p class="apache">Apache HTTP Server Version 2.3</p>
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21 <div id="page-content">
22 <div id="preamble"><h1>Apache Module mod_file_cache</h1>
24 <p><span>Available Languages: </span><a href="../en/mod/mod_file_cache.html" title="English"> en </a> |
25 <a href="../ko/mod/mod_file_cache.html" hreflang="ko" rel="alternate" title=""> ko </a></p>
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>
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
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>
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>
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>
59 <div id="quickview"><h3 class="directives">Directives</h3>
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>
66 <li><img alt="" src="../images/down.gif" /> <a href="#using">Using mod_file_cache</a></li>
68 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
70 <h2><a name="using" id="using">Using mod_file_cache</a></h2>
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>
75 <p>Not all platforms support both directives. For example, Apache
76 on Windows does not currently support the <code class="directive"><a href="#mmapstatic">MMapStatic</a></code> directive, while
77 other platforms, like AIX, support both. You will receive an error
78 message in the server error log if you attempt to use an
79 unsupported directive. If given an unsupported directive, the
80 server will start but the file will not be cached. On platforms
81 that support both directives, you should experiment with both to
82 see which works best for you.</p>
84 <h3>MMapFile Directive</h3>
86 <p>The <code class="directive"><a href="#mmapfile">MMapFile</a></code>
87 directive of <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> maps a list of
88 statically configured files into memory through the system call
89 <code>mmap()</code>. This system call is available on most modern
90 Unix derivates, but not on all. There are sometimes system-specific
91 limits on the size and number of files that can be
92 <code>mmap()</code>ed, experimentation is probably the easiest way
95 <p>This <code>mmap()</code>ing is done once at server start or
96 restart, only. So whenever one of the mapped files changes on the
97 filesystem you <em>have</em> to restart the server (see the <a href="../stopping.html">Stopping and Restarting</a> documentation).
98 To reiterate that point: if the files are modified <em>in place</em>
99 without restarting the server you may end up serving requests that
100 are completely bogus. You should update files by unlinking the old
101 copy and putting a new copy in place. Most tools such as
102 <code>rdist</code> and <code>mv</code> do this. The reason why this
103 modules doesn't take care of changes to the files is that this check
104 would need an extra <code>stat()</code> every time which is a waste
105 and against the intent of I/O reduction.</p>
108 <h3>CacheFile Directive</h3>
110 <p>The <code class="directive"><a href="#cachefile">CacheFile</a></code>
111 directive of <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> opens an active
112 <em>handle</em> or <em>file descriptor</em> to the file (or files)
113 listed in the configuration directive and places these open file
114 handles in the cache. When the file is requested, the server
115 retrieves the handle from the cache and passes it to the
116 <code>sendfile()</code> (or <code>TransmitFile()</code> on Windows),
121 <p>This file handle caching is done once at server start or
122 restart, only. So whenever one of the cached files changes on
123 the filesystem you <em>have</em> to restart the server (see the
124 <a href="../stopping.html">Stopping and Restarting</a>
125 documentation). To reiterate that point: if the files are
126 modified <em>in place</em> without restarting the server you
127 may end up serving requests that are completely bogus. You
128 should update files by unlinking the old copy and putting a new
129 copy in place. Most tools such as <code>rdist</code> and
130 <code>mv</code> do this.</p>
133 <div class="note"><h3>Note</h3>
134 <p>Don't bother asking for a directive which recursively
135 caches all the files in a directory. Try this instead... See the
136 <code class="directive"><a href="../mod/core.html#include">Include</a></code> directive, and consider
139 <div class="example"><p><code>
140 find /www/htdocs -type f -print \<br />
141 | sed -e 's/.*/mmapfile &/' > /www/conf/mmap.conf
145 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
146 <div class="directive-section"><h2><a name="CacheFile" id="CacheFile">CacheFile</a> <a name="cachefile" id="cachefile">Directive</a></h2>
147 <table class="directive">
148 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Cache a list of file handles at startup time</td></tr>
149 <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>
150 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
151 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
152 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_file_cache</td></tr>
154 <p>The <code class="directive">CacheFile</code> directive opens handles to
155 one or more files (given as whitespace separated arguments) and
156 places these handles into the cache at server startup
157 time. Handles to cached files are automatically closed on a server
158 shutdown. When the files have changed on the filesystem, the
159 server should be restarted to to re-cache them.</p>
161 <p>Be careful with the <var>file-path</var> arguments: They have
162 to literally match the filesystem path Apache's URL-to-filename
163 translation handlers create. We cannot compare inodes or other
164 stuff to match paths through symbolic links <em>etc.</em>
165 because that again would cost extra <code>stat()</code> system
166 calls which is not acceptable. This module may or may not work
167 with filenames rewritten by <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> or
168 <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.</p>
170 <div class="example"><h3>Example</h3><p><code>
171 CacheFile /usr/local/apache/htdocs/index.html
175 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
176 <div class="directive-section"><h2><a name="MMapFile" id="MMapFile">MMapFile</a> <a name="mmapfile" id="mmapfile">Directive</a></h2>
177 <table class="directive">
178 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Map a list of files into memory at startup time</td></tr>
179 <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>
180 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
181 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
182 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_file_cache</td></tr>
184 <p>The <code class="directive">MMapFile</code> directive maps one or more files
185 (given as whitespace separated arguments) into memory at server
186 startup time. They are automatically unmapped on a server
187 shutdown. When the files have changed on the filesystem at
188 least a <code>HUP</code> or <code>USR1</code> signal should be send to
189 the server to re-<code>mmap()</code> them.</p>
191 <p>Be careful with the <var>file-path</var> arguments: They have
192 to literally match the filesystem path Apache's URL-to-filename
193 translation handlers create. We cannot compare inodes or other
194 stuff to match paths through symbolic links <em>etc.</em>
195 because that again would cost extra <code>stat()</code> system
196 calls which is not acceptable. This module may or may not work
197 with filenames rewritten by <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> or
198 <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.</p>
200 <div class="example"><h3>Example</h3><p><code>
201 MMapFile /usr/local/apache/htdocs/index.html
206 <div class="bottomlang">
207 <p><span>Available Languages: </span><a href="../en/mod/mod_file_cache.html" title="English"> en </a> |
208 <a href="../ko/mod/mod_file_cache.html" hreflang="ko" rel="alternate" title=""> ko </a></p>
209 </div><div id="footer">
210 <p class="apache">Copyright 2006 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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