2 <!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
3 <?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
4 <!-- $LastChangedRevision$ -->
7 Licensed to the Apache Software Foundation (ASF) under one or more
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9 this work for additional information regarding copyright ownership.
10 The ASF licenses this file to You under the Apache License, Version 2.0
11 (the "License"); you may not use this file except in compliance with
12 the License. You may obtain a copy of the License at
14 http://www.apache.org/licenses/LICENSE-2.0
16 Unless required by applicable law or agreed to in writing, software
17 distributed under the License is distributed on an "AS IS" BASIS,
18 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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23 <modulesynopsis metafile="mod_file_cache.xml.meta">
25 <name>mod_file_cache</name>
26 <description>Caches a static list of files in memory</description>
27 <status>Experimental</status>
28 <sourcefile>mod_file_cache.c</sourcefile>
29 <identifier>file_cache_module</identifier>
34 This module should be used with care. You can easily create a broken
35 site using <module>mod_file_cache</module>, 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 <module>mod_file_cache</module> provides two techniques for caching
42 frequently requested <em>static</em> files. Through configuration
43 directives, you can direct <module>mod_file_cache</module> 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>
59 <section id="using"><title>Using mod_file_cache</title>
61 <p><module>mod_file_cache</module> caches a list of statically
62 configured files via <directive module="mod_file_cache"
63 >MMapFile</directive> or <directive module="mod_file_cache"
64 >CacheFile</directive> directives in the main server configuration.</p>
66 <p>Not all platforms support both directives. You will receive an error
67 message in the server error log if you attempt to use an
68 unsupported directive. If given an unsupported directive, the
69 server will start but the file will not be cached. On platforms
70 that support both directives, you should experiment with both to
71 see which works best for you.</p>
73 <section><title>MMapFile Directive</title>
75 <p>The <directive module="mod_file_cache">MMapFile</directive>
76 directive of <module>mod_file_cache</module> maps a list of
77 statically configured files into memory through the system call
78 <code>mmap()</code>. This system call is available on most modern
79 Unix derivatives, but not on all. There are sometimes system-specific
80 limits on the size and number of files that can be
81 <code>mmap()</code>ed, experimentation is probably the easiest way
84 <p>This <code>mmap()</code>ing is done once at server start or
85 restart, only. So whenever one of the mapped files changes on the
86 filesystem you <em>have</em> to restart the server (see the <a
87 href="../stopping.html">Stopping and Restarting</a> documentation).
88 To reiterate that point: if the files are modified <em>in place</em>
89 without restarting the server you may end up serving requests that
90 are completely bogus. You should update files by unlinking the old
91 copy and putting a new copy in place. Most tools such as
92 <code>rdist</code> and <code>mv</code> do this. The reason why this
93 modules doesn't take care of changes to the files is that this check
94 would need an extra <code>stat()</code> every time which is a waste
95 and against the intent of I/O reduction.</p>
98 <section><title>CacheFile Directive</title>
100 <p>The <directive module="mod_file_cache">CacheFile</directive>
101 directive of <module>mod_file_cache</module> opens an active
102 <em>handle</em> or <em>file descriptor</em> to the file (or files)
103 listed in the configuration directive and places these open file
104 handles in the cache. When the file is requested, the server
105 retrieves the handle from the cache and passes it to the
106 <code>sendfile()</code> (or <code>TransmitFile()</code> on Windows),
110 <p>Insert more details about sendfile API...</p>
113 <p>This file handle caching is done once at server start or
114 restart, only. So whenever one of the cached files changes on
115 the filesystem you <em>have</em> to restart the server (see the
116 <a href="../stopping.html">Stopping and Restarting</a>
117 documentation). To reiterate that point: if the files are
118 modified <em>in place</em> without restarting the server you
119 may end up serving requests that are completely bogus. You
120 should update files by unlinking the old copy and putting a new
121 copy in place. Most tools such as <code>rdist</code> and
122 <code>mv</code> do this.</p>
125 <note><title>Note</title>
126 <p>Don't bother asking for a directive which recursively
127 caches all the files in a directory. Try this instead... See the
128 <directive module="core">Include</directive> directive, and consider
132 find /www/htdocs -type f -print \<br />
133 | sed -e 's/.*/mmapfile &/' > /www/conf/mmap.conf
139 <name>MMapFile</name>
140 <description>Map a list of files into memory at startup time</description>
141 <syntax>MMapFile <var>file-path</var> [<var>file-path</var>] ...</syntax>
142 <contextlist><context>server config</context></contextlist>
145 <p>The <directive>MMapFile</directive> directive maps one or more files
146 (given as whitespace separated arguments) into memory at server
147 startup time. They are automatically unmapped on a server
148 shutdown. When the files have changed on the filesystem at
149 least a <code>HUP</code> or <code>USR1</code> signal should be send to
150 the server to re-<code>mmap()</code> them.</p>
152 <p>Be careful with the <var>file-path</var> arguments: They have
153 to literally match the filesystem path Apache's URL-to-filename
154 translation handlers create. We cannot compare inodes or other
155 stuff to match paths through symbolic links <em>etc.</em>
156 because that again would cost extra <code>stat()</code> system
157 calls which is not acceptable. This module may or may not work
158 with filenames rewritten by <module>mod_alias</module> or
159 <module>mod_rewrite</module>.</p>
161 <example><title>Example</title>
162 MMapFile /usr/local/apache/htdocs/index.html
168 <name>CacheFile</name>
169 <description>Cache a list of file handles at startup time</description>
170 <syntax>CacheFile <var>file-path</var> [<var>file-path</var>] ...</syntax>
171 <contextlist><context>server config</context></contextlist>
174 <p>The <directive>CacheFile</directive> directive opens handles to
175 one or more files (given as whitespace separated arguments) and
176 places these handles into the cache at server startup
177 time. Handles to cached files are automatically closed on a server
178 shutdown. When the files have changed on the filesystem, the
179 server should be restarted to re-cache them.</p>
181 <p>Be careful with the <var>file-path</var> arguments: They have
182 to literally match the filesystem path Apache's URL-to-filename
183 translation handlers create. We cannot compare inodes or other
184 stuff to match paths through symbolic links <em>etc.</em>
185 because that again would cost extra <code>stat()</code> system
186 calls which is not acceptable. This module may or may not work
187 with filenames rewritten by <module>mod_alias</module> or
188 <module>mod_rewrite</module>.</p>
190 <example><title>Example</title>
191 CacheFile /usr/local/apache/htdocs/index.html