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10 <title>mod_file_cache - Apache HTTP Server Version 2.5</title>
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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&component=mod_file_cache">Report a bug</a></li></ul><h3>See also</h3>
75 <li><a href="#comments_section">Comments</a></li></ul></div>
76 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
78 <h2><a name="using" id="using">Using mod_file_cache</a> <a title="Permanent link" href="#using" class="permalink">¶</a></h2>
80 <p><code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> caches a list of statically
81 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>
83 <p>Not all platforms support both directives. You will receive an error
84 message in the server error log if you attempt to use an
85 unsupported directive. If given an unsupported directive, the
86 server will start but the file will not be cached. On platforms
87 that support both directives, you should experiment with both to
88 see which works best for you.</p>
90 <h3>MMapFile Directive</h3>
92 <p>The <code class="directive"><a href="#mmapfile">MMapFile</a></code>
93 directive of <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> maps a list of
94 statically configured files into memory through the system call
95 <code>mmap()</code>. This system call is available on most modern
96 Unix derivatives, but not on all. There are sometimes system-specific
97 limits on the size and number of files that can be
98 <code>mmap()</code>ed, experimentation is probably the easiest way
101 <p>This <code>mmap()</code>ing is done once at server start or
102 restart, only. So whenever one of the mapped files changes on the
103 filesystem you <em>have</em> to restart the server (see the <a href="../stopping.html">Stopping and Restarting</a> documentation).
104 To reiterate that point: if the files are modified <em>in place</em>
105 without restarting the server you may end up serving requests that
106 are completely bogus. You should update files by unlinking the old
107 copy and putting a new copy in place. Most tools such as
108 <code>rdist</code> and <code>mv</code> do this. The reason why this
109 modules doesn't take care of changes to the files is that this check
110 would need an extra <code>stat()</code> every time which is a waste
111 and against the intent of I/O reduction.</p>
114 <h3>CacheFile Directive</h3>
116 <p>The <code class="directive"><a href="#cachefile">CacheFile</a></code>
117 directive of <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> opens an active
118 <em>handle</em> or <em>file descriptor</em> to the file (or files)
119 listed in the configuration directive and places these open file
120 handles in the cache. When the file is requested, the server
121 retrieves the handle from the cache and passes it to the
122 <code>sendfile()</code> (or <code>TransmitFile()</code> on Windows),
127 <p>This file handle caching is done once at server start or
128 restart, only. So whenever one of the cached files changes on
129 the filesystem you <em>have</em> to restart the server (see the
130 <a href="../stopping.html">Stopping and Restarting</a>
131 documentation). To reiterate that point: if the files are
132 modified <em>in place</em> without restarting the server you
133 may end up serving requests that are completely bogus. You
134 should update files by unlinking the old copy and putting a new
135 copy in place. Most tools such as <code>rdist</code> and
136 <code>mv</code> do this.</p>
139 <div class="note"><h3>Note</h3>
140 <p>Don't bother asking for a directive which recursively
141 caches all the files in a directory. Try this instead... See the
142 <code class="directive"><a href="../mod/core.html#include">Include</a></code> directive, and consider
145 <div class="example"><p><code>
146 find /www/htdocs -type f -print \<br />
147 | sed -e 's/.*/mmapfile &/' > /www/conf/mmap.conf
151 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
152 <div class="directive-section"><h2><a name="CacheFile" id="CacheFile">CacheFile</a> <a name="cachefile" id="cachefile">Directive</a> <a title="Permanent link" href="#cachefile" class="permalink">¶</a></h2>
153 <table class="directive">
154 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Cache a list of file handles at startup time</td></tr>
155 <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>
156 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
157 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
158 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_file_cache</td></tr>
160 <p>The <code class="directive">CacheFile</code> directive opens handles to
161 one or more files (given as whitespace separated arguments) and
162 places these handles into the cache at server startup
163 time. Handles to cached files are automatically closed on a server
164 shutdown. When the files have changed on the filesystem, the
165 server should be restarted to re-cache them.</p>
167 <p>Be careful with the <var>file-path</var> arguments: They have
168 to literally match the filesystem path Apache's URL-to-filename
169 translation handlers create. We cannot compare inodes or other
170 stuff to match paths through symbolic links <em>etc.</em>
171 because that again would cost extra <code>stat()</code> system
172 calls which is not acceptable. This module may or may not work
173 with filenames rewritten by <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> or
174 <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.</p>
176 <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">CacheFile /usr/local/apache/htdocs/index.html</pre>
180 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
181 <div class="directive-section"><h2><a name="MMapFile" id="MMapFile">MMapFile</a> <a name="mmapfile" id="mmapfile">Directive</a> <a title="Permanent link" href="#mmapfile" class="permalink">¶</a></h2>
182 <table class="directive">
183 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Map a list of files into memory at startup time</td></tr>
184 <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>
185 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr>
186 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Experimental</td></tr>
187 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_file_cache</td></tr>
189 <p>The <code class="directive">MMapFile</code> directive maps one or more files
190 (given as whitespace separated arguments) into memory at server
191 startup time. They are automatically unmapped on a server
192 shutdown. When the files have changed on the filesystem at
193 least a <code>HUP</code> or <code>USR1</code> signal should be send to
194 the server to re-<code>mmap()</code> them.</p>
196 <p>Be careful with the <var>file-path</var> arguments: They have
197 to literally match the filesystem path Apache's URL-to-filename
198 translation handlers create. We cannot compare inodes or other
199 stuff to match paths through symbolic links <em>etc.</em>
200 because that again would cost extra <code>stat()</code> system
201 calls which is not acceptable. This module may or may not work
202 with filenames rewritten by <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> or
203 <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.</p>
205 <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">MMapFile /usr/local/apache/htdocs/index.html</pre>
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211 <p><span>Available Languages: </span><a href="../en/mod/mod_file_cache.html" title="English"> en </a> |
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213 <a href="../ko/mod/mod_file_cache.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
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