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<modulesynopsis metafile="mod_file_cache.xml.meta">

<name>mod_file_cache</name>

<description>Caches a static list of files in memory</description>

<status>Experimental</status>

<sourcefile>mod_file_cache.c</sourcefile>

<identifier>file_cache_module</identifier>

<summary>

<note type="warning">

This module should be used with care. You can easily create a broken

site using <module>mod_file_cache</module>, so read this document

carefully.

</note>

<p><em>Caching</em> frequently requested files that change very

infrequently is a technique for reducing server load.

<module>mod_file_cache</module> provides two techniques for caching

frequently requested <em>static</em> files. Through configuration

directives, you can direct <module>mod_file_cache</module> to either

open then <code>mmap()</code> a file, or to pre-open a file and save

the file's open <em>file handle</em>. Both techniques reduce server

load when processing requests for these files by doing part of the work

(specifically, the file I/O) for serving the file when the

server is started rather than during each request.</p>

<p>Notice: You cannot use this for speeding up CGI programs or

other files which are served by special content handlers. It

can only be used for regular files which are usually served by

the Apache core content handler.</p>

<p>This module is an extension of and borrows heavily from the

<code>mod_mmap_static</code> module in Apache 1.3.</p>

</summary>

<section id="using"><title>Using mod_file_cache</title>

<p><module>mod_file_cache</module> caches a list of statically

configured files via <directive module="mod_file_cache"

>MMapFile</directive> or <directive module="mod_file_cache"

>CacheFile</directive> directives in the main server configuration.</p>

<p>Not all platforms support both directives. You will receive an error

message in the server error log if you attempt to use an

unsupported directive. If given an unsupported directive, the

server will start but the file will not be cached. On platforms

that support both directives, you should experiment with both to

see which works best for you.</p>

<section><title>MMapFile Directive</title>

<p>The <directive module="mod_file_cache">MMapFile</directive>

directive of <module>mod_file_cache</module> maps a list of

statically configured files into memory through the system call

<code>mmap()</code>. This system call is available on most modern

Unix derivatives, but not on all. There are sometimes system-specific

limits on the size and number of files that can be

<code>mmap()</code>ed, experimentation is probably the easiest way

to find out.</p>

<p>This <code>mmap()</code>ing is done once at server start or

restart, only. So whenever one of the mapped files changes on the

filesystem you <em>have</em> to restart the server (see the <a

href="/stopping.html">Stopping and Restarting</a> documentation).

To reiterate that point: if the files are modified <em>in place</em>

without restarting the server you may end up serving requests that

are completely bogus. You should update files by unlinking the old

copy and putting a new copy in place. Most tools such as

<code>rdist</code> and <code>mv</code> do this. The reason why this

modules doesn't take care of changes to the files is that this check

would need an extra <code>stat()</code> every time which is a waste

and against the intent of I/O reduction.</p>

</section>

<section><title>CacheFile Directive</title>

<p>The <directive module="mod_file_cache">CacheFile</directive>

directive of <module>mod_file_cache</module> opens an active

<em>handle</em> or <em>file descriptor</em> to the file (or files)

listed in the configuration directive and places these open file

handles in the cache. When the file is requested, the server

retrieves the handle from the cache and passes it to the

<code>sendfile()</code> (or <code>TransmitFile()</code> on Windows),

socket API.</p>

<!-- XXX

<p>This file handle caching is done once at server start or

restart, only. So whenever one of the cached files changes on

the filesystem you <em>have</em> to restart the server (see the

<a href="/stopping.html">Stopping and Restarting</a>

documentation). To reiterate that point: if the files are

modified <em>in place</em> without restarting the server you

may end up serving requests that are completely bogus. You

should update files by unlinking the old copy and putting a new

copy in place. Most tools such as <code>rdist</code> and

<code>mv</code> do this.</p>

</section>

<note><title>Note</title>

<p>Don't bother asking for a directive which recursively

caches all the files in a directory. Try this instead... See the

<directive module="core">Include</directive> directive, and consider

this command:</p>

<example>

find /www/htdocs -type f -print \<br />

| sed -e 's/.*/mmapfile &amp;/' &gt; /www/conf/mmap.conf

</example>

</note>

</section>

<directivesynopsis>

<name>MMapFile</name>

<description>Map a list of files into memory at startup time</description>

<syntax>MMapFile <var>file-path</var> [<var>file-path</var>] ...</syntax>

<contextlist><context>server config</context></contextlist>

<usage>

<p>The <directive>MMapFile</directive> directive maps one or more files

(given as whitespace separated arguments) into memory at server

startup time. They are automatically unmapped on a server

shutdown. When the files have changed on the filesystem at

least a <code>HUP</code> or <code>USR1</code> signal should be send to

the server to re-<code>mmap()</code> them.</p>

<p>Be careful with the <var>file-path</var> arguments: They have

to literally match the filesystem path Apache's URL-to-filename

translation handlers create. We cannot compare inodes or other

stuff to match paths through symbolic links <em>etc.</em>

because that again would cost extra <code>stat()</code> system

calls which is not acceptable. This module may or may not work

with filenames rewritten by <module>mod_alias</module> or

<module>mod_rewrite</module>.</p>

<example><title>Example</title>

MMapFile /usr/local/apache/htdocs/index.html

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>CacheFile</name>

<description>Cache a list of file handles at startup time</description>

<syntax>CacheFile <var>file-path</var> [<var>file-path</var>] ...</syntax>

<contextlist><context>server config</context></contextlist>

<usage>

<p>The <directive>CacheFile</directive> directive opens handles to

one or more files (given as whitespace separated arguments) and

places these handles into the cache at server startup

time. Handles to cached files are automatically closed on a server

shutdown. When the files have changed on the filesystem, the

server should be restarted to re-cache them.</p>

<p>Be careful with the <var>file-path</var> arguments: They have

to literally match the filesystem path Apache's URL-to-filename

translation handlers create. We cannot compare inodes or other

stuff to match paths through symbolic links <em>etc.</em>

because that again would cost extra <code>stat()</code> system

calls which is not acceptable. This module may or may not work

with filenames rewritten by <module>mod_alias</module> or

<module>mod_rewrite</module>.</p>

<example><title>Example</title>

CacheFile /usr/local/apache/htdocs/index.html

</example>

</usage>

</directivesynopsis>

</modulesynopsis>