2 <!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
3 <?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
6 Copyright 2002-2004 The Apache Software Foundation
8 Licensed under the Apache License, Version 2.0 (the "License");
9 you may not use this file except in compliance with the License.
10 You may obtain a copy of the License at
12 http://www.apache.org/licenses/LICENSE-2.0
14 Unless required by applicable law or agreed to in writing, software
15 distributed under the License is distributed on an "AS IS" BASIS,
16 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
17 See the License for the specific language governing permissions and
18 limitations under the License.
21 <modulesynopsis metafile="mod_file_cache.xml.meta">
23 <name>mod_file_cache</name>
24 <description>Caches a static list of files in memory</description>
25 <status>Experimental</status>
26 <sourcefile>mod_file_cache.c</sourcefile>
27 <identifier>file_cache_module</identifier>
32 This module should be used with care. You can easily create a broken
33 site using <module>mod_file_cache</module>, so read this document
37 <p><em>Caching</em> frequently requested files that change very
38 infrequently is a technique for reducing server load.
39 <module>mod_file_cache</module> provides two techniques for caching
40 frequently requested <em>static</em> files. Through configuration
41 directives, you can direct <module>mod_file_cache</module> to either
42 open then <code>mmap()</code> a file, or to pre-open a file and save
43 the file's open <em>file handle</em>. Both techniques reduce server
44 load when processing requests for these files by doing part of the work
45 (specifically, the file I/O) for serving the file when the
46 server is started rather than during each request.</p>
48 <p>Notice: You cannot use this for speeding up CGI programs or
49 other files which are served by special content handlers. It
50 can only be used for regular files which are usually served by
51 the Apache core content handler.</p>
53 <p>This module is an extension of and borrows heavily from the
54 <code>mod_mmap_static</code> module in Apache 1.3.</p>
57 <section id="using"><title>Using mod_file_cache</title>
59 <p><module>mod_file_cache</module> caches a list of statically
60 configured files via <directive module="mod_file_cache"
61 >MMapFile</directive> or <directive module="mod_file_cache"
62 >CacheFile</directive> directives in the main server configuration.</p>
64 <p>Not all platforms support both directives. For example, Apache
65 on Windows does not currently support the <directive
66 module="mod_file_cache">MMapStatic</directive> directive, while
67 other platforms, like AIX, support both. You will receive an error
68 message in the server error log if you attempt to use an
69 unsupported directive. If given an unsupported directive, the
70 server will start but the file will not be cached. On platforms
71 that support both directives, you should experiment with both to
72 see which works best for you.</p>
74 <section><title>MMapFile Directive</title>
76 <p>The <directive module="mod_file_cache">MMapFile</directive>
77 directive of <module>mod_file_cache</module> maps a list of
78 statically configured files into memory through the system call
79 <code>mmap()</code>. This system call is available on most modern
80 Unix derivates, but not on all. There are sometimes system-specific
81 limits on the size and number of files that can be
82 <code>mmap()</code>ed, experimentation is probably the easiest way
85 <p>This <code>mmap()</code>ing is done once at server start or
86 restart, only. So whenever one of the mapped files changes on the
87 filesystem you <em>have</em> to restart the server (see the <a
88 href="../stopping.html">Stopping and Restarting</a> documentation).
89 To reiterate that point: if the files are modified <em>in place</em>
90 without restarting the server you may end up serving requests that
91 are completely bogus. You should update files by unlinking the old
92 copy and putting a new copy in place. Most tools such as
93 <code>rdist</code> and <code>mv</code> do this. The reason why this
94 modules doesn't take care of changes to the files is that this check
95 would need an extra <code>stat()</code> every time which is a waste
96 and against the intent of I/O reduction.</p>
99 <section><title>CacheFile Directive</title>
101 <p>The <directive module="mod_file_cache">CacheFile</directive>
102 directive of <module>mod_file_cache</module> opens an active
103 <em>handle</em> or <em>file descriptor</em> to the file (or files)
104 listed in the configuration directive and places these open file
105 handles in the cache. When the file is requested, the server
106 retrieves the handle from the cache and passes it to the
107 <code>sendfile()</code> (or <code>TransmitFile()</code> on Windows),
111 <p>Insert more details about sendfile API...</p>
114 <p>This file handle caching is done once at server start or
115 restart, only. So whenever one of the cached files changes on
116 the filesystem you <em>have</em> to restart the server (see the
117 <a href="../stopping.html">Stopping and Restarting</a>
118 documentation). To reiterate that point: if the files are
119 modified <em>in place</em> without restarting the server you
120 may end up serving requests that are completely bogus. You
121 should update files by unlinking the old copy and putting a new
122 copy in place. Most tools such as <code>rdist</code> and
123 <code>mv</code> do this.</p>
126 <note><title>Note</title>
127 <p>Don't bother asking for a for a directive which recursively
128 caches all the files in a directory. Try this instead... See the
129 <directive module="core">Include</directive> directive, and consider
133 find /www/htdocs -type f -print \<br />
134 | sed -e 's/.*/mmapfile &/' > /www/conf/mmap.conf
140 <name>MMapFile</name>
141 <description>Map a list of files into memory at startup time</description>
142 <syntax>MMapFile <var>file-path</var> [<var>file-path</var>] ...</syntax>
143 <contextlist><context>server config</context></contextlist>
146 <p>The <directive>MMapFile</directive> directive maps one or more files
147 (given as whitespace separated arguments) into memory at server
148 startup time. They are automatically unmapped on a server
149 shutdown. When the files have changed on the filesystem at
150 least a <code>HUP</code> or <code>USR1</code> signal should be send to
151 the server to re-<code>mmap()</code> them.</p>
153 <p>Be careful with the <var>file-path</var> arguments: They have
154 to literally match the filesystem path Apache's URL-to-filename
155 translation handlers create. We cannot compare inodes or other
156 stuff to match paths through symbolic links <em>etc.</em>
157 because that again would cost extra <code>stat()</code> system
158 calls which is not acceptable. This module may or may not work
159 with filenames rewritten by <module>mod_alias</module> or
160 <module>mod_rewrite</module>.</p>
162 <example><title>Example</title>
163 MMapFile /usr/local/apache/htdocs/index.html
169 <name>CacheFile</name>
170 <description>Cache a list of file handles at startup time</description>
171 <syntax>CacheFile <var>file-path</var> [<var>file-path</var>] ...</syntax>
172 <contextlist><context>server config</context></contextlist>
175 <p>The <directive>CacheFile</directive> directive opens handles to
176 one or more files (given as whitespace separated arguments) and
177 places these handles into the cache at server startup
178 time. Handles to cached files are automatically closed on a server
179 shutdown. When the files have changed on the filesystem, the
180 server should be restarted to to re-cache them.</p>
182 <p>Be careful with the <var>file-path</var> arguments: They have
183 to literally match the filesystem path Apache's URL-to-filename
184 translation handlers create. We cannot compare inodes or other
185 stuff to match paths through symbolic links <em>etc.</em>
186 because that again would cost extra <code>stat()</code> system
187 calls which is not acceptable. This module may or may not work
188 with filenames rewritten by <module>mod_alias</module> or
189 <module>mod_rewrite</module>.</p>
191 <example><title>Example</title>
192 CacheFile /usr/local/apache/htdocs/index.html