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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></p>
26 <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>
27 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
28 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>file_cache_module</td></tr>
29 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_file_cache.c</td></tr></table>
34 This module should be used with care. You can easily create a broken
35 site using <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code>, so read this document
39 <p><em>Caching</em> frequently requested files that change very
40 infrequently is a technique for reducing server load.
41 <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> provides two techniques for caching
42 frequently requested <em>static</em> files. Through configuration
43 directives, you can direct <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> to either
44 open then <code>mmap()</code> a file, or to pre-open a file and save
45 the file's open <em>file handle</em>. Both techniques reduce server
46 load when processing requests for these files by doing part of the work
47 (specifically, the file I/O) for serving the file when the
48 server is started rather than during each request.</p>
50 <p>Notice: You cannot use this for speeding up CGI programs or
51 other files which are served by special content handlers. It
52 can only be used for regular files which are usually served by
53 the Apache core content handler.</p>
55 <p>This module is an extension of and borrows heavily from the
56 <code>mod_mmap_static</code> module in Apache 1.3.</p>
58 <div id="quickview"><h3 class="directives">Directives</h3>
60 <li><img alt="" src="../images/down.gif" /> <a href="#cachefile">CacheFile</a></li>
61 <li><img alt="" src="../images/down.gif" /> <a href="#mmapfile">MMapFile</a></li>
65 <li><img alt="" src="../images/down.gif" /> <a href="#using">Using mod_file_cache</a></li>
67 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
69 <h2><a name="using" id="using">Using mod_file_cache</a></h2>
71 <p><code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> caches a list of statically
72 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 <p>Not all platforms support both directives. For example, Apache
75 on Windows does not currently support the <code class="directive"><a href="#mmapstatic">MMapStatic</a></code> directive, while
76 other platforms, like AIX, support both. You will receive an error
77 message in the server error log if you attempt to use an
78 unsupported directive. If given an unsupported directive, the
79 server will start but the file will not be cached. On platforms
80 that support both directives, you should experiment with both to
81 see which works best for you.</p>
83 <h3>MMapFile Directive</h3>
85 <p>The <code class="directive"><a href="#mmapfile">MMapFile</a></code>
86 directive of <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> maps a list of
87 statically configured files into memory through the system call
88 <code>mmap()</code>. This system call is available on most modern
89 Unix derivates, but not on all. There are sometimes system-specific
90 limits on the size and number of files that can be
91 <code>mmap()</code>ed, experimentation is probably the easiest way
94 <p>This <code>mmap()</code>ing is done once at server start or
95 restart, only. So whenever one of the mapped files changes on the
96 filesystem you <em>have</em> to restart the server (see the <a href="../stopping.html">Stopping and Restarting</a> documentation).
97 To reiterate that point: if the files are modified <em>in place</em>
98 without restarting the server you may end up serving requests that
99 are completely bogus. You should update files by unlinking the old
100 copy and putting a new copy in place. Most tools such as
101 <code>rdist</code> and <code>mv</code> do this. The reason why this
102 modules doesn't take care of changes to the files is that this check
103 would need an extra <code>stat()</code> every time which is a waste
104 and against the intent of I/O reduction.</p>
107 <h3>CacheFile Directive</h3>
109 <p>The <code class="directive"><a href="#cachefile">CacheFile</a></code>
110 directive of <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> opens an active
111 <em>handle</em> or <em>file descriptor</em> to the file (or files)
112 listed in the configuration directive and places these open file
113 handles in the cache. When the file is requested, the server
114 retrieves the handle from the cache and passes it to the
115 <code>sendfile()</code> (or <code>TransmitFile()</code> on Windows),
120 <p>This file handle caching is done once at server start or
121 restart, only. So whenever one of the cached files changes on
122 the filesystem you <em>have</em> to restart the server (see the
123 <a href="../stopping.html">Stopping and Restarting</a>
124 documentation). To reiterate that point: if the files are
125 modified <em>in place</em> without restarting the server you
126 may end up serving requests that are completely bogus. You
127 should update files by unlinking the old copy and putting a new
128 copy in place. Most tools such as <code>rdist</code> and
129 <code>mv</code> do this.</p>
132 <div class="note"><h3>Note</h3>
133 <p>Don't bother asking for a for a directive which recursively
134 caches all the files in a directory. Try this instead... See the
135 <code class="directive"><a href="../mod/core.html#include">Include</a></code> directive, and consider
138 <div class="example"><p><code>
139 find /www/htdocs -type f -print \<br />
140 | sed -e 's/.*/mmapfile &/' > /www/conf/mmap.conf
144 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
145 <div class="directive-section"><h2><a name="CacheFile" id="CacheFile">CacheFile</a> <a name="cachefile" id="cachefile">Directive</a></h2>
146 <table class="directive">
147 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Cache a list of file handles at startup time</td></tr>
148 <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>
149 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
150 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
151 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_file_cache</td></tr>
153 <p>The <code class="directive">CacheFile</code> directive opens handles to
154 one or more files (given as whitespace separated arguments) and
155 places these handles into the cache at server startup
156 time. Handles to cached files are automatically closed on a server
157 shutdown. When the files have changed on the filesystem, the
158 server should be restarted to to re-cache them.</p>
160 <p>Be careful with the <var>file-path</var> arguments: They have
161 to literally match the filesystem path Apache's URL-to-filename
162 translation handlers create. We cannot compare inodes or other
163 stuff to match paths through symbolic links <em>etc.</em>
164 because that again would cost extra <code>stat()</code> system
165 calls which is not acceptable. This module may or may not work
166 with filenames rewritten by <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> or
167 <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.</p>
169 <div class="example"><h3>Example</h3><p><code>
170 CacheFile /usr/local/apache/htdocs/index.html
174 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
175 <div class="directive-section"><h2><a name="MMapFile" id="MMapFile">MMapFile</a> <a name="mmapfile" id="mmapfile">Directive</a></h2>
176 <table class="directive">
177 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Map a list of files into memory at startup time</td></tr>
178 <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>
179 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
180 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
181 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_file_cache</td></tr>
183 <p>The <code class="directive">MMapFile</code> directive maps one or more files
184 (given as whitespace separated arguments) into memory at server
185 startup time. They are automatically unmapped on a server
186 shutdown. When the files have changed on the filesystem at
187 least a <code>HUP</code> or <code>USR1</code> signal should be send to
188 the server to re-<code>mmap()</code> them.</p>
190 <p>Be careful with the <var>file-path</var> arguments: They have
191 to literally match the filesystem path Apache's URL-to-filename
192 translation handlers create. We cannot compare inodes or other
193 stuff to match paths through symbolic links <em>etc.</em>
194 because that again would cost extra <code>stat()</code> system
195 calls which is not acceptable. This module may or may not work
196 with filenames rewritten by <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> or
197 <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.</p>
199 <div class="example"><h3>Example</h3><p><code>
200 MMapFile /usr/local/apache/htdocs/index.html
205 <div class="bottomlang">
206 <p><span>Available Languages: </span><a href="../en/mod/mod_file_cache.html" title="English"> en </a></p>
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