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<title>mod_cache_disk - Apache HTTP Server Version 2.5</title>
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<p class="apache">Apache HTTP Server Version 2.5</p>
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<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.5</a> > <a href="./">Modules</a></div>
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<div id="preamble"><h1>Apache Module mod_cache_disk</h1>
<div class="toplang">
<p><span>Available Languages: </span><a href="/en/mod/mod_cache_disk.html" title="English"> en </a> |
<a href="/fr/mod/mod_cache_disk.html" hreflang="fr" rel="alternate" title="Fran�ais"> fr </a> |
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<a href="/ko/mod/mod_cache_disk.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
</div>
<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Disk based storage module for the HTTP caching filter.</td></tr>
<tr><th><a href="module-dict.html#ModuleIdentifier">Module�Identifier:</a></th><td>cache_disk_module</td></tr>
<tr><th><a href="module-dict.html#SourceFile">Source�File:</a></th><td>mod_cache_disk.c</td></tr></table>
<h3>Summary</h3>
<p><code class="module"><a href="/mod/mod_cache_disk.html">mod_cache_disk</a></code> implements a disk based storage
<p>The headers and bodies of cached responses are stored separately on
disk, in a directory structure derived from the md5 hash of the cached
URL.</p>
<p>Multiple content negotiated responses can be stored concurrently,
however the caching of partial content is not yet supported by this
module.</p>
<p>Atomic cache updates to both header and body files are achieved
without the need for locking by storing the device and inode numbers of
the body file within the header file. This has the side effect that
cache entries manually moved into the cache will be ignored.</p>
<p>The <code class="program"><a href="/programs/htcacheclean.html">htcacheclean</a></code> tool is provided to list cached
URLs, remove cached URLs, or to maintain the size of the disk cache
can be daemonized to offer continuous monitoring of directory sizes.</p>
<div class="note"><h3>Note:</h3>
<p><code class="module"><a href="/mod/mod_cache_disk.html">mod_cache_disk</a></code> requires the services of
loaded before mod_cache_disk.</p>
</div>
<div class="note"><h3>Note:</h3>
<p><code class="module"><a href="/mod/mod_cache_disk.html">mod_cache_disk</a></code> uses the sendfile feature to
serve files from the cache when supported by the platform, and
when enabled with <code class="directive"><a href="/mod/core.html#enablesendfile">EnableSendfile</a></code>.
However, per-directory and .htaccess configuration of
<code class="directive"><a href="/mod/core.html#enablesendfile">EnableSendfile</a></code> are ignored by
<code class="module"><a href="/mod/mod_cache_disk.html">mod_cache_disk</a></code> as the corresponding settings are not
available to the module when a request is being served from the
cache.</p>
</div>
</div>
<div id="quickview"><h3 class="directives">Directives</h3>
<ul id="toc">
</ul>
<h3>See also</h3>
<ul class="seealso">
</ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
<div class="directive-section"><h2><a name="CacheDirLength" id="CacheDirLength">CacheDirLength</a> <a name="cachedirlength" id="cachedirlength">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The number of characters in subdirectory names</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheDirLength <var>length</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheDirLength 2</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
</table>
<p>The <code class="directive">CacheDirLength</code> directive sets the number
of characters for each subdirectory name in the cache hierarchy. It can
be used in conjunction with <code class="directive">CacheDirLevels</code> to
determine the approximate structure of your cache hierarchy.</p>
<p>A high value for <code class="directive">CacheDirLength</code> combined
with a low value for <code class="directive">CacheDirLevels</code> will result in
a relatively flat hierarchy, with a large number of subdirectories at each
level.</p>
<div class="note">
<p>The result of <code class="directive"><a href="#cachedirlevels">CacheDirLevels</a></code>* <code class="directive">CacheDirLength</code>
must not be higher than 20.</p>
</div>
</div>
<div class="directive-section"><h2><a name="CacheDirLevels" id="CacheDirLevels">CacheDirLevels</a> <a name="cachedirlevels" id="cachedirlevels">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The number of levels of subdirectories in the
cache.</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheDirLevels <var>levels</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheDirLevels 2</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
</table>
<p>The <code class="directive">CacheDirLevels</code> directive sets the number
of subdirectory levels in the cache. Cached data will be saved this
many directory levels below the <code class="directive"><a href="#cacheroot">CacheRoot</a></code> directory.</p>
<p>A high value for <code class="directive">CacheDirLevels</code> combined
with a low value for <code class="directive">CacheDirLength</code> will result in
a relatively deep hierarchy, with a small number of subdirectories at each
level.</p>
<div class="note">
<p>The result of <code class="directive">CacheDirLevels</code>*
<code class="directive"><a href="#cachedirlength">CacheDirLength</a></code> must
not be higher than 20.</p>
</div>
</div>
<div class="directive-section"><h2><a name="CacheMaxFileSize" id="CacheMaxFileSize">CacheMaxFileSize</a> <a name="cachemaxfilesize" id="cachemaxfilesize">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The maximum size (in bytes) of a document to be placed in the
cache</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheMaxFileSize <var>bytes</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheMaxFileSize 1000000</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
</table>
<p>The <code class="directive">CacheMaxFileSize</code> directive sets the
maximum size, in bytes, for a document to be considered for storage in
the cache.</p>
<pre class="prettyprint lang-config">CacheMaxFileSize 64000</pre>
</div>
<div class="directive-section"><h2><a name="CacheMinFileSize" id="CacheMinFileSize">CacheMinFileSize</a> <a name="cacheminfilesize" id="cacheminfilesize">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The minimum size (in bytes) of a document to be placed in the
cache</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheMinFileSize <var>bytes</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheMinFileSize 1</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
</table>
<p>The <code class="directive">CacheMinFileSize</code> directive sets the
minimum size, in bytes, for a document to be considered for storage
in the cache.</p>
<pre class="prettyprint lang-config">CacheMinFileSize 64</pre>
</div>
<div class="directive-section"><h2><a name="CacheReadSize" id="CacheReadSize">CacheReadSize</a> <a name="cachereadsize" id="cachereadsize">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The minimum size (in bytes) of the document to read and be cached
before sending the data downstream</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheReadSize <var>bytes</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheReadSize 0</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
</table>
<p>The <code class="directive">CacheReadSize</code> directive sets the
minimum amount of data, in bytes, to be read from the backend before the
data is sent to the client. The default of zero causes all data read of
any size to be passed downstream to the client immediately as it arrives.
Setting this to a higher value causes the disk cache to buffer at least
this amount before sending the result to the client. This can improve
performance when caching content from a reverse proxy.</p>
<p>This directive only takes effect when the data is being saved to the
cache, as opposed to data being served from the cache.</p>
<pre class="prettyprint lang-config">CacheReadSize 102400</pre>
</div>
<div class="directive-section"><h2><a name="CacheReadTime" id="CacheReadTime">CacheReadTime</a> <a name="cachereadtime" id="cachereadtime">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The minimum time (in milliseconds) that should elapse while reading
before data is sent downstream</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheReadTime <var>milliseconds</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheReadTime 0</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
</table>
<p>The <code class="directive">CacheReadTime</code> directive sets the minimum amount
of elapsed time that should pass before making an attempt to send data
downstream to the client. During the time period, data will be buffered
before sending the result to the client. This can improve performance when
caching content from a reverse proxy.</p>
<p>The default of zero disables this option.</p>
<p>This directive only takes effect when the data is being saved to the
cache, as opposed to data being served from the cache. It is recommended
that this option be used alongside the
<code class="directive"><a href="#cachereadsize">CacheReadSize</a></code> directive to
ensure that the server does not buffer excessively should data arrive faster
than expected.</p>
<pre class="prettyprint lang-config">CacheReadTime 1000</pre>
</div>
<div class="directive-section"><h2><a name="CacheRoot" id="CacheRoot">CacheRoot</a> <a name="cacheroot" id="cacheroot">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The directory root under which cache files are
stored</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheRoot <var>directory</var></code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr>
</table>
<p>The <code class="directive">CacheRoot</code> directive defines the name of
the directory on the disk to contain cache files. If the <code class="module"><a href="/mod/mod_cache_disk.html">mod_cache_disk</a></code> module has been loaded or compiled in to the
Apache server, this directive <em>must</em> be defined. Failing to
provide a value for <code class="directive">CacheRoot</code> will result in
a configuration file processing error. The <code class="directive"><a href="#cachedirlevels">CacheDirLevels</a></code> and <code class="directive"><a href="#cachedirlength">CacheDirLength</a></code> directives define
the structure of the directories under the specified root directory.</p>
<pre class="prettyprint lang-config">CacheRoot c:/cacheroot</pre>
</div>
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<p><span>Available Languages: </span><a href="/en/mod/mod_cache_disk.html" title="English"> en </a> |
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<a href="/ko/mod/mod_cache_disk.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
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