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160 lines
11 KiB
Plaintext
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--><title>mod_file_cache - Apache HTTP Server</title><link href="../style/manual.css" type="text/css" rel="stylesheet"/></head><body><blockquote><div align="center"><img src="../images/sub.gif" alt="[APACHE DOCUMENTATION]"/><h3>Apache HTTP Server Version 2.0</h3></div><h1 align="center">Apache Module mod_file_cache</h1><table cellspacing="1" cellpadding="0" bgcolor="#cccccc"><tr><td><table bgcolor="#ffffff"><tr><td nowrap="nowrap" valign="top"><span class="help">Description:
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</span></td><td>Caches a static list of files in memory</td></tr><tr><td nowrap="nowrap"><a href="module-dict.html#Status" class="help">Status:
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</a></td><td>Experimental</td></tr><tr><td nowrap="nowrap"><a href="module-dict.html#ModuleIdentifier" class="help">Module Identifier:
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</a></td><td>file_cache_module</td></tr></table></td></tr></table><h2>Summary</h2>
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<blockquote><table><tr><td bgcolor="#ffe5f5">
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This module should be used with care. You can easily
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create a broken site using mod_file_cache, so read this
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document carefully.
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</td></tr></table></blockquote>
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<p><em>Caching</em> frequently requested files that change very
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infrequently is a technique for reducing server load.
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mod_file_cache provides two techniques for caching frequently
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requested <em>static</em> files. Through configuration
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directives, you can direct mod_file_cache to either open then
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mmap()a file, or to pre-open a file and save the file's open
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<em>file handle</em>. Both techniques reduce server load when
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processing requests for these files by doing part of the work
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(specifically, the file I/O) for serving the file when the
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server is started rather than during each request.</p>
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<p>Notice: You cannot use this for speeding up CGI programs or
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other files which are served by special content handlers. It
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can only be used for regular files which are usually served by
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the Apache core content handler.</p>
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<p>This module is an extension of and borrows heavily from the
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mod_mmap_static module in Apache 1.3.</p>
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<h2>Directives</h2><ul><li><a href="#cachefile">CacheFile</a></li><li><a href="#mmapfile">MMapFile</a></li></ul><h2>Using mod_file_cache</h2>
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<p><code><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> caches a list of statically
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configured files via <a href="#mmapfile" class="directive"><code class="directive">MMapFile</code></a> or <a href="#cachefile" class="directive"><code class="directive">CacheFile</code></a> directives in the
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main server configuration.</p>
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<p>Not all platforms support both directives. For example, Apache
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on Windows does not currently support the <a href="#mmapstatic" class="directive"><code class="directive">MMapStatic</code></a> directive, while
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other platforms, like AIX, support both. You will receive an error
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message in the server error log if you attempt to use an
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unsupported directive. If given an unsupported directive, the
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server will start but the file will not be cached. On platforms
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that support both directives, you should experiment with both to
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see which works best for you.</p>
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<h3>MmapFile Directive</h3>
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<p>The <a href="#mmapfile" class="directive"><code class="directive">MmapFile</code></a>
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directive of <code><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> maps a list of
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statically configured files into memory through the system call
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<code>mmap()</code>. This system call is available on most modern
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Unix derivates, but not on all. There are sometimes
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system-specific limits on the size and number of files that can be
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mmap()d, experimentation is probably the easiest way to find
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out.</p>
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<p>This mmap()ing is done once at server start or restart,
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only. So whenever one of the mapped files changes on the
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filesystem you <em>have</em> to restart the server (see the <a href="../stopping.html">Stopping and Restarting</a>
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documentation). To reiterate that point: if the files are
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modified <em>in place</em> without restarting the server you
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may end up serving requests that are completely bogus. You
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should update files by unlinking the old copy and putting a new
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copy in place. Most tools such as <code>rdist</code> and
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<code>mv</code> do this. The reason why this modules doesn't
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take care of changes to the files is that this check would need
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an extra <code>stat()</code> every time which is a waste and
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against the intent of I/O reduction.</p>
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<h3>CacheFile Directive</h3>
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<p>The <a href="#cachefile" class="directive"><code class="directive">CacheFile</code></a>
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directive of <code><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> opens an active
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<em>handle</em> or <em>file descriptor</em> to the file (or files)
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listed in the configuration directive and places these open file
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handles in the cache. When the file is requested, the server
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retrieves the handle from the cache and passes it to the
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sendfile() (or TransmitFile() on Windows), socket API.</p>
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<p>Insert more details about sendfile API...</p>
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<p>This file handle caching is done once at server start or
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restart, only. So whenever one of the cached files changes on
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the filesystem you <em>have</em> to restart the server (see the
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<a href="../stopping.html">Stopping and Restarting</a>
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documentation). To reiterate that point: if the files are
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modified <em>in place</em> without restarting the server you
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may end up serving requests that are completely bogus. You
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should update files by unlinking the old copy and putting a new
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copy in place. Most tools such as <code>rdist</code> and
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<code>mv</code> do this.</p>
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<blockquote><table><tr><td bgcolor="#e0e5f5"><p align="center"><strong>Note</strong></p> Don't bother asking for a for a
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directive which recursively caches all the files in a
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directory. Try this instead... See the
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<a href="../mod/core.html#include" class="directive"><code class="directive">Include</code></a> directive, and consider
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this command:
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<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
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find /www/htdocs -type f -print \ <br>
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| sed -e 's/.*/mmapfile &/' > /www/conf/mmap.conf
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</code></td></tr></table></blockquote>
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</td></tr></table></blockquote>
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<hr/><h2><a name="CacheFile">CacheFile</a> <a name="cachefile">Directive</a></h2><table cellpadding="1" cellspacing="0" border="0" bgcolor="#cccccc"><tr><td><table bgcolor="#ffffff"><tr><td nowrap="nowrap"><strong>Description:
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</strong></td><td/></tr><tr><td nowrap="nowrap"><a href="directive-dict.html#Syntax" class="help">Syntax:
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</a></td><td>CacheFile
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<em>file-path</em> [<em>file-path</em>] ...</td></tr><tr><td nowrap="nowrap"><a href="directive-dict.html#Context" class="help">Context:
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</a></td><td>server config</td></tr><tr><td nowrap="nowrap"><a href="directive-dict.html#Status" class="help">Status:
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</a></td><td>Experimental</td></tr><tr><td nowrap="nowrap"><a href="directive-dict.html#Module" class="help">Module:
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</a></td><td>mod_file_cache</td></tr></table></td></tr></table>
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<p>The <code class="directive">CacheFile</code> directive opens handles to
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one or more files (given as whitespace separated arguments) and
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places these handles into the cache at server startup
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time. Handles to cached files are automatically closed on a server
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shutdown. When the files have changed on the filesystem, the
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server should be restarted to to re-cache them.</p>
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<p>Be careful with the <em>file-path</em> arguments: They have
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to literally match the filesystem path Apache's URL-to-filename
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translation handlers create. We cannot compare inodes or other
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stuff to match paths through symbolic links <em>etc.</em>
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because that again would cost extra <code>stat()</code> system
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calls which is not acceptable. This module may or may not work
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with filenames rewritten by <code><a href="../mod/mod_alias.html">mod_alias</a></code> or
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<code><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.</p>
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<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><p align="center"><strong>Example</strong></p><code>
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CacheFile /usr/local/apache/htdocs/index.html
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</code></td></tr></table></blockquote>
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<hr/><h2><a name="MMapFile">MMapFile</a> <a name="mmapfile">Directive</a></h2><table cellpadding="1" cellspacing="0" border="0" bgcolor="#cccccc"><tr><td><table bgcolor="#ffffff"><tr><td nowrap="nowrap"><strong>Description:
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</strong></td><td/></tr><tr><td nowrap="nowrap"><a href="directive-dict.html#Syntax" class="help">Syntax:
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</a></td><td>MMapFile <em>file-path</em> [<em>file-path</em>] ...</td></tr><tr><td nowrap="nowrap"><a href="directive-dict.html#Context" class="help">Context:
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</a></td><td>server config</td></tr><tr><td nowrap="nowrap"><a href="directive-dict.html#Status" class="help">Status:
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</a></td><td>Experimental</td></tr><tr><td nowrap="nowrap"><a href="directive-dict.html#Module" class="help">Module:
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</a></td><td>mod_file_cache</td></tr></table></td></tr></table>
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<p>The <code class="directive">MMapFile</code> directive maps one or more files
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(given as whitespace separated arguments) into memory at server
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startup time. They are automatically unmapped on a server
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shutdown. When the files have changed on the filesystem at
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least a HUP or USR1 signal should be send to the server to
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re-mmap them.</p>
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<p>Be careful with the <em>file-path</em> arguments: They have
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to literally match the filesystem path Apache's URL-to-filename
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translation handlers create. We cannot compare inodes or other
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stuff to match paths through symbolic links <em>etc.</em>
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because that again would cost extra <code>stat()</code> system
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calls which is not acceptable. This module may or may not work
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with filenames rewritten by <code><a href="../mod/mod_alias.html">mod_alias</a></code> or
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<code><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.</p>
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<blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><p align="center"><strong>Example</strong></p><code>
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MMapFile /usr/local/apache/htdocs/index.html
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</code></td></tr></table></blockquote>
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<hr/></blockquote><h3 align="center">Apache HTTP Server Version 2.0</h3><a href="./"><img src="../images/index.gif" alt="Index"/></a><a href="../"><img src="../images/home.gif" alt="Home"/></a></body></html> |