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| <p class="apache">Apache HTTP Server Version 2.4</p> |
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| <div id="preamble"><h1>Apache Module mod_file_cache</h1> |
| <div class="toplang"> |
| <p><span>Available Languages: </span><a href="../en/mod/mod_file_cache.html" title="English"> en </a> | |
| <a href="../fr/mod/mod_file_cache.html" hreflang="fr" rel="alternate" title="Français"> fr </a> | |
| <a href="../ko/mod/mod_file_cache.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p> |
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| <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> |
| <tr><th><a href="module-dict.html#Status">Status:</a></th><td>Experimental</td></tr> |
| <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>file_cache_module</td></tr> |
| <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_file_cache.c</td></tr></table> |
| <h3>Summary</h3> |
| |
| |
| <div class="warning"> |
| This module should be used with care. You can easily create a broken |
| site using <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code>, so read this document |
| carefully. |
| </div> |
| |
| <p><em>Caching</em> frequently requested files that change very |
| infrequently is a technique for reducing server load. |
| <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> provides two techniques for caching |
| frequently requested <em>static</em> files. Through configuration |
| directives, you can direct <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> 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> |
| </div> |
| <div id="quickview"><a href="https://www.apache.org/foundation/contributing.html" class="badge"><img src="https://www.apache.org/images/SupportApache-small.png" alt="Support Apache!" /></a><h3>Topics</h3> |
| <ul id="topics"> |
| <li><img alt="" src="../images/down.gif" /> <a href="#using">Using mod_file_cache</a></li> |
| </ul><h3 class="directives">Directives</h3> |
| <ul id="toc"> |
| <li><img alt="" src="../images/down.gif" /> <a href="#cachefile">CacheFile</a></li> |
| <li><img alt="" src="../images/down.gif" /> <a href="#mmapfile">MMapFile</a></li> |
| </ul> |
| <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> |
| <ul class="seealso"> |
| <li><a href="#comments_section">Comments</a></li></ul></div> |
| <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> |
| <div class="section"> |
| <h2><a name="using" id="using">Using mod_file_cache</a></h2> |
| |
| <p><code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> caches a list of statically |
| 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> |
| |
| <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> |
| |
| <h3>MMapFile Directive</h3> |
| |
| <p>The <code class="directive"><a href="#mmapfile">MMapFile</a></code> |
| directive of <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> 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> |
| |
| |
| <h3>CacheFile Directive</h3> |
| |
| <p>The <code class="directive"><a href="#cachefile">CacheFile</a></code> |
| directive of <code class="module"><a href="../mod/mod_file_cache.html">mod_file_cache</a></code> 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> |
| |
| |
| |
| <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> |
| |
| |
| <div class="note"><h3>Note</h3> |
| <p>Don't bother asking for a directive which recursively |
| caches all the files in a directory. Try this instead... See the |
| <code class="directive"><a href="../mod/core.html#include">Include</a></code> directive, and consider |
| this command:</p> |
| |
| <div class="example"><p><code> |
| find /www/htdocs -type f -print \<br /> |
| | sed -e 's/.*/mmapfile &/' > /www/conf/mmap.conf |
| </code></p></div> |
| </div> |
| </div> |
| <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> |
| <div class="directive-section"><h2><a name="CacheFile" id="CacheFile">CacheFile</a> <a name="cachefile" id="cachefile">Directive</a></h2> |
| <table class="directive"> |
| <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Cache a list of file handles at startup time</td></tr> |
| <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> |
| <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr> |
| <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Experimental</td></tr> |
| <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_file_cache</td></tr> |
| </table> |
| <p>The <code class="directive">CacheFile</code> 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 <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> or |
| <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.</p> |
| |
| <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">CacheFile /usr/local/apache/htdocs/index.html</pre> |
| </div> |
| |
| </div> |
| <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> |
| <div class="directive-section"><h2><a name="MMapFile" id="MMapFile">MMapFile</a> <a name="mmapfile" id="mmapfile">Directive</a></h2> |
| <table class="directive"> |
| <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Map a list of files into memory at startup time</td></tr> |
| <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> |
| <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config</td></tr> |
| <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Experimental</td></tr> |
| <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_file_cache</td></tr> |
| </table> |
| <p>The <code class="directive">MMapFile</code> 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 <code class="module"><a href="../mod/mod_alias.html">mod_alias</a></code> or |
| <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>.</p> |
| |
| <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">MMapFile /usr/local/apache/htdocs/index.html</pre> |
| </div> |
| |
| </div> |
| </div> |
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| <a href="../ko/mod/mod_file_cache.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p> |
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