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<title>mod_cache_disk - Apache HTTP Server Version 2.4</title>
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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">&nbsp;en&nbsp;</a> |
<a href="../fr/mod/mod_cache_disk.html" hreflang="fr" rel="alternate" title="Franais">&nbsp;fr&nbsp;</a> |
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<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#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="module-dict.html#ModuleIdentifier">ModuleIdentifier:</a></th><td>cache_disk_module</td></tr>
<tr><th><a href="module-dict.html#SourceFile">SourceFile:</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
    manager for <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code>.</p>

    <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
    within size and/or inode limits. The tool can be run on demand, or
    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
      <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code>, which must be
      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"><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 class="directives">Directives</h3>
<ul id="toc">
<li><img alt="" src="../images/down.gif" /> <a href="#cachedirlength">CacheDirLength</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#cachedirlevels">CacheDirLevels</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#cachemaxfilesize">CacheMaxFileSize</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#cacheminfilesize">CacheMinFileSize</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#cachereadsize">CacheReadSize</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#cachereadtime">CacheReadTime</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#cacheroot">CacheRoot</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__&amp;list_id=144532&amp;product=Apache%20httpd-2&amp;query_format=specific&amp;order=changeddate%20DESC%2Cpriority%2Cbug_severity&amp;component=mod_cache_disk">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2&amp;component=mod_cache_disk">Report a bug</a></li></ul><h3>See also</h3>
<ul class="seealso">
<li><code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code></li>
<li><code class="module"><a href="../mod/mod_cache_socache.html">mod_cache_socache</a></code></li>
<li><a href="../caching.html">Caching Guide</a></li>
<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="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>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache_disk</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="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></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>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache_disk</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="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></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>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache_disk</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="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></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>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache_disk</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="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></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>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache_disk</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="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></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>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache_disk</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="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></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>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache_disk</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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