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21 <p class="apache">Apache HTTP Server Version 2.5</p>
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25 <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 2.5</a> > <a href="./">Modules</a></div>
26 <div id="page-content">
27 <div id="preamble"><h1>Apache Module mod_file_cache</h1>
29 <p><span>Available Languages: </span><a href="../en/mod/mod_file_cache.html" title="English"> en </a> |
30 <a href="../fr/mod/mod_file_cache.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
31 <a href="../ko/mod/mod_file_cache.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
33 <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>
34 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
35 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>file_cache_module</td></tr>
36 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_file_cache.c</td></tr></table>
41 This module should be used with care. You can easily create a broken
42 site using <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code>, so read this document
46 <p><em>Caching</em> frequently requested files that change very
47 infrequently is a technique for reducing server load.
48 <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> provides two techniques for caching
49 frequently requested <em>static</em> files. Through configuration
50 directives, you can direct <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> to either
51 open then <code>mmap()</code> a file, or to pre-open a file and save
52 the file's open <em>file handle</em>. Both techniques reduce server
53 load when processing requests for these files by doing part of the work
54 (specifically, the file I/O) for serving the file when the
55 server is started rather than during each request.</p>
57 <p>Notice: You cannot use this for speeding up CGI programs or
58 other files which are served by special content handlers. It
59 can only be used for regular files which are usually served by
60 the Apache core content handler.</p>
62 <p>This module is an extension of and borrows heavily from the
63 <code>mod_mmap_static</code> module in Apache 1.3.</p>
65 <div id="quickview"><h3>Topics</h3>
67 <li><img alt="" src="../images/down.gif" /> <a href="#using">Using mod_file_cache</a></li>
68 </ul><h3 class="directives">Directives</h3>
70 <li><img alt="" src="../images/down.gif" /> <a href="#cachefile">CacheFile</a></li>
71 <li><img alt="" src="../images/down.gif" /> <a href="#mmapfile">MMapFile</a></li>
73 <h3>Bugfix checklist:</h3><ul class="seealso"><li><a href="https://www.apache.org/dist/httpd/CHANGES_2.4">HTTPD changelog</a></li><li><a href="https://bz.apache.org/bugzilla/buglist.cgi?bug_status=__open__&list_id=144532&product=Apache%20httpd-2&query_format=specific&order=changeddate%20DESC%2Cpriority%2Cbug_severity&component=mod_file_cache">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2">Report a bug</a></li></ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
74 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
76 <h2><a name="using" id="using">Using mod_file_cache</a></h2>
78 <p><code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> caches a list of statically
79 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>
81 <p>Not all platforms support both directives. You will receive an error
82 message in the server error log if you attempt to use an
83 unsupported directive. If given an unsupported directive, the
84 server will start but the file will not be cached. On platforms
85 that support both directives, you should experiment with both to
86 see which works best for you.</p>
88 <h3>MMapFile Directive</h3>
90 <p>The <code class="directive"><a href="#mmapfile">MMapFile</a></code>
91 directive of <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> maps a list of
92 statically configured files into memory through the system call
93 <code>mmap()</code>. This system call is available on most modern
94 Unix derivatives, but not on all. There are sometimes system-specific
95 limits on the size and number of files that can be
96 <code>mmap()</code>ed, experimentation is probably the easiest way
99 <p>This <code>mmap()</code>ing is done once at server start or
100 restart, only. So whenever one of the mapped files changes on the
101 filesystem you <em>have</em> to restart the server (see the <a href="../stopping.html">Stopping and Restarting</a> documentation).
102 To reiterate that point: if the files are modified <em>in place</em>
103 without restarting the server you may end up serving requests that
104 are completely bogus. You should update files by unlinking the old
105 copy and putting a new copy in place. Most tools such as
106 <code>rdist</code> and <code>mv</code> do this. The reason why this
107 modules doesn't take care of changes to the files is that this check
108 would need an extra <code>stat()</code> every time which is a waste
109 and against the intent of I/O reduction.</p>
112 <h3>CacheFile Directive</h3>
114 <p>The <code class="directive"><a href="#cachefile">CacheFile</a></code>
115 directive of <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> opens an active
116 <em>handle</em> or <em>file descriptor</em> to the file (or files)
117 listed in the configuration directive and places these open file
118 handles in the cache. When the file is requested, the server
119 retrieves the handle from the cache and passes it to the
120 <code>sendfile()</code> (or <code>TransmitFile()</code> on Windows),
125 <p>This file handle caching is done once at server start or
126 restart, only. So whenever one of the cached files changes on
127 the filesystem you <em>have</em> to restart the server (see the
128 <a href="../stopping.html">Stopping and Restarting</a>
129 documentation). To reiterate that point: if the files are
130 modified <em>in place</em> without restarting the server you
131 may end up serving requests that are completely bogus. You
132 should update files by unlinking the old copy and putting a new
133 copy in place. Most tools such as <code>rdist</code> and
134 <code>mv</code> do this.</p>
137 <div class="note"><h3>Note</h3>
138 <p>Don't bother asking for a directive which recursively
139 caches all the files in a directory. Try this instead... See the
140 <code class="directive"><a href="../mod/core.html#include">Include</a></code> directive, and consider
143 <div class="example"><p><code>
144 find /www/htdocs -type f -print \<br />
145 | sed -e 's/.*/mmapfile &/' > /www/conf/mmap.conf
149 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
150 <div class="directive-section"><h2><a name="CacheFile" id="CacheFile">CacheFile</a> <a name="cachefile" id="cachefile">Directive</a></h2>
151 <table class="directive">
152 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Cache a list of file handles at startup time</td></tr>
153 <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>
154 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
155 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
156 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_file_cache</td></tr>
158 <p>The <code class="directive">CacheFile</code> directive opens handles to
159 one or more files (given as whitespace separated arguments) and
160 places these handles into the cache at server startup
161 time. Handles to cached files are automatically closed on a server
162 shutdown. When the files have changed on the filesystem, the
163 server should be restarted to re-cache them.</p>
165 <p>Be careful with the <var>file-path</var> arguments: They have
166 to literally match the filesystem path Apache's URL-to-filename
167 translation handlers create. We cannot compare inodes or other
168 stuff to match paths through symbolic links <em>etc.</em>
169 because that again would cost extra <code>stat()</code> system
170 calls which is not acceptable. This module may or may not work
171 with filenames rewritten by <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> or
172 <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.</p>
174 <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">CacheFile /usr/local/apache/htdocs/index.html</pre>
178 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
179 <div class="directive-section"><h2><a name="MMapFile" id="MMapFile">MMapFile</a> <a name="mmapfile" id="mmapfile">Directive</a></h2>
180 <table class="directive">
181 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Map a list of files into memory at startup time</td></tr>
182 <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>
183 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
184 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
185 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_file_cache</td></tr>
187 <p>The <code class="directive">MMapFile</code> directive maps one or more files
188 (given as whitespace separated arguments) into memory at server
189 startup time. They are automatically unmapped on a server
190 shutdown. When the files have changed on the filesystem at
191 least a <code>HUP</code> or <code>USR1</code> signal should be send to
192 the server to re-<code>mmap()</code> them.</p>
194 <p>Be careful with the <var>file-path</var> arguments: They have
195 to literally match the filesystem path Apache's URL-to-filename
196 translation handlers create. We cannot compare inodes or other
197 stuff to match paths through symbolic links <em>etc.</em>
198 because that again would cost extra <code>stat()</code> system
199 calls which is not acceptable. This module may or may not work
200 with filenames rewritten by <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> or
201 <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.</p>
203 <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">MMapFile /usr/local/apache/htdocs/index.html</pre>
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209 <p><span>Available Languages: </span><a href="../en/mod/mod_file_cache.html" title="English"> en </a> |
210 <a href="../fr/mod/mod_file_cache.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
211 <a href="../ko/mod/mod_file_cache.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
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