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<div id="preamble"><h1>Apache Module mod_cache</h1>
<div class="toplang">
<p><span>Available Languages: </span><a href="../en/mod/mod_cache.html" title="English">&nbsp;en&nbsp;</a> |
<a href="../ja/mod/mod_cache.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
<a href="../ko/mod/mod_cache.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a></p>
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<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Content cache keyed to URIs.</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">Module Identifier:</a></th><td>cache_module</td></tr>
<tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_cache.c</td></tr></table>
<h3>Summary</h3>

    <div class="warning">This module should be used with care and
    can be used to circumvent <code class="directive"><a href="../mod/mod_authz_host.html#allow">Allow</a></code> and <code class="directive"><a href="../mod/mod_authz_host.html#deny">Deny</a></code> directives. You 
    should not enable caching for any content to which you wish
    to limit access by client host name, address or environment
    variable.</div>  

    <p><code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> implements an <a href="http://www.ietf.org/rfc/rfc2616.txt">RFC 2616</a> compliant HTTP
    content cache that can be used to cache either local or proxied content.
    <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> requires the services of one or more storage
    management modules. Two storage management modules are included in
    the base Apache distribution:</p>
    <dl>
    <dt><code class="module"><a href="../mod/mod_disk_cache.html">mod_disk_cache</a></code></dt>
    <dd>implements a disk based storage manager.</dd>

    <dt><code class="module"><a href="../mod/mod_mem_cache.html">mod_mem_cache</a></code></dt>
    <dd>implements a memory based storage manager. 
    <code class="module"><a href="../mod/mod_mem_cache.html">mod_mem_cache</a></code> can be configured to operate in two
    modes: caching open file descriptors or caching objects in heap storage.
    <code class="module"><a href="../mod/mod_mem_cache.html">mod_mem_cache</a></code> can be used to cache locally generated content
    or to cache backend server content for <code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code> when
    configured using <code class="directive"><a href="../mod/mod_proxy.html#proxypass">ProxyPass</a></code>
    (aka <dfn>reverse proxy</dfn>)</dd>
    </dl>

    <p>Content is stored in and retrieved from the cache using URI based keys. Content with
    access protection is not cached.</p>
    <p>Further details, discussion, and examples, are provided in the
    <a href="../caching.html">Caching Guide</a>.</p>
</div>
<div id="quickview"><h3 class="directives">Directives</h3>
<ul id="toc">
<li><img alt="" src="../images/down.gif" /> <a href="#cachedefaultexpire">CacheDefaultExpire</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#cachedisable">CacheDisable</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#cacheenable">CacheEnable</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#cacheignorecachecontrol">CacheIgnoreCacheControl</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#cacheignoreheaders">CacheIgnoreHeaders</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#cacheignorenolastmod">CacheIgnoreNoLastMod</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#cacheignorequerystring">CacheIgnoreQueryString</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#cacheignoreurlsessionidentifiers">CacheIgnoreURLSessionIdentifiers</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#cachelastmodifiedfactor">CacheLastModifiedFactor</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#cachelock">CacheLock</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#cachelockmaxage">CacheLockMaxAge</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#cachelockpath">CacheLockPath</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#cachemaxexpire">CacheMaxExpire</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#cachestorenostore">CacheStoreNoStore</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#cachestoreprivate">CacheStorePrivate</a></li>
</ul>
<h3>Topics</h3>
<ul id="topics">
<li><img alt="" src="../images/down.gif" /> <a href="#related">Related Modules and Directives</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#sampleconf">Sample Configuration</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#thunderingherd">Avoiding the Thundering Herd</a></li>
</ul><h3>See also</h3>
<ul class="seealso">
<li><a href="../caching.html">Caching Guide</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="related" id="related">Related Modules and Directives</a></h2>
    <table class="related"><tr><th>Related Modules</th><th>Related Directives</th></tr><tr><td><ul><li><code class="module"><a href="../mod/mod_disk_cache.html">mod_disk_cache</a></code></li><li><code class="module"><a href="../mod/mod_mem_cache.html">mod_mem_cache</a></code></li></ul></td><td><ul><li><code class="directive"><a href="../mod/mod_disk_cache.html#cacheroot">CacheRoot</a></code></li><li><code class="directive"><a href="../mod/mod_disk_cache.html#cachedirlevels">CacheDirLevels</a></code></li><li><code class="directive"><a href="../mod/mod_disk_cache.html#cachedirlength">CacheDirLength</a></code></li><li><code class="directive"><a href="../mod/mod_disk_cache.html#cacheminfilesize">CacheMinFileSize</a></code></li><li><code class="directive"><a href="../mod/mod_disk_cache.html#cachemaxfilesize">CacheMaxFileSize</a></code></li><li><code class="directive"><a href="../mod/mod_mem_cache.html#mcachesize">MCacheSize</a></code></li><li><code class="directive"><a href="../mod/mod_mem_cache.html#mcachemaxobjectcount">MCacheMaxObjectCount</a></code></li><li><code class="directive"><a href="../mod/mod_mem_cache.html#mcacheminobjectsize">MCacheMinObjectSize</a></code></li><li><code class="directive"><a href="../mod/mod_mem_cache.html#mcachemaxobjectsize">MCacheMaxObjectSize</a></code></li><li><code class="directive"><a href="../mod/mod_mem_cache.html#mcacheremovalalgorithm">MCacheRemovalAlgorithm</a></code></li><li><code class="directive"><a href="../mod/mod_mem_cache.html#mcachemaxstreamingbuffer">MCacheMaxStreamingBuffer</a></code></li></ul></td></tr></table>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="sampleconf" id="sampleconf">Sample Configuration</a></h2>
    <div class="example"><h3>Sample httpd.conf</h3><p><code>
      #<br />
      # Sample Cache Configuration<br />
      #<br />
      LoadModule cache_module modules/mod_cache.so<br />
      <br />
      &lt;IfModule mod_cache.c&gt;<br />
      <span class="indent">
        #LoadModule disk_cache_module modules/mod_disk_cache.so<br />
        # If you want to use mod_disk_cache instead of mod_mem_cache,<br />
        # uncomment the line above and comment out the LoadModule line below.<br />
        &lt;IfModule mod_disk_cache.c&gt;<br />
        <span class="indent">
          CacheRoot c:/cacheroot<br />
          CacheEnable disk  /<br />
          CacheDirLevels 5<br />
          CacheDirLength 3<br />
        </span>
        &lt;/IfModule&gt; <br />
        <br />
        LoadModule mem_cache_module modules/mod_mem_cache.so<br />
        &lt;IfModule mod_mem_cache.c&gt;<br />
        <span class="indent">
          CacheEnable mem  /<br />
          MCacheSize 4096<br />
          MCacheMaxObjectCount 100<br />
          MCacheMinObjectSize 1<br />
          MCacheMaxObjectSize 2048<br />
        </span>
        &lt;/IfModule&gt;<br />
        <br />
        # When acting as a proxy, don't cache the list of security updates<br />
        CacheDisable http://security.update.server/update-list/<br />
      </span>
      &lt;/IfModule&gt;
    </code></p></div>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="thunderingherd" id="thunderingherd">Avoiding the Thundering Herd</a></h2>
  <p>When a cached entry becomes stale, <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> will submit
  a conditional request to the backend, which is expected to confirm whether the
  cached entry is still fresh, and send an updated entity if not.</p>
  <p>A small but finite amount of time exists between the time the cached entity
  becomes stale, and the time the stale entity is fully refreshed. On a busy
  server, a significant number of requests might arrive during this time, and
  cause a <strong>thundering herd</strong> of requests to strike the backend
  suddenly and unpredicably.</p>
  <p>To keep the thundering herd at bay, the <code class="directive">CacheLock</code>
  directive can be used to define a directory in which locks are created for
  URLs <strong>in flight</strong>. The lock is used as a <strong>hint</strong>
  by other requests to either suppress an attempt to cache (someone else has
  gone to fetch the entity), or to indicate that a stale entry is being refreshed
  (stale content will be returned in the mean time).
  </p>
  <h3>Initial caching of an entry</h3>
    
    <p>When an entity is cached for the first time, a lock will be created for the
    entity until the response has been fully cached. During the lifetime of the
    lock, the cache will suppress the second and subsequent attempt to cache the
    same entity. While this doesn't hold back the thundering herd, it does stop
    the cache attempting to cache the same entity multiple times simultaneously.
    </p>
  
  <h3>Refreshment of a stale entry</h3>
    
    <p>When an entity reaches its freshness lifetime and becomes stale, a lock
    will be created for the entity until the response has either been confirmed as
    still fresh, or replaced by the backend. During the lifetime of the lock, the
    second and subsequent incoming request will cause stale data to be returned,
    and the thundering herd is kept at bay.</p>
  
  <h3>Locks and Cache-Control: no-cache</h3>
    
    <p>Locks are used as a <strong>hint only</strong> to enable the cache to be
    more gentle on backend servers, however the lock can be overridden if necessary.
    If the client sends a request with a Cache-Control header forcing a reload, any
    lock that may be present will be ignored, and the client's request will be
    honoured immediately and the cached entry refreshed.</p>
    <p>As a further safety mechanism, locks have a configurable maximum age.
    Once this age has been reached, the lock is removed, and a new request is
    given the opportunity to create a new lock. This maximum age can be set using
    the <code class="directive">CacheLockMaxAge</code> directive, and defaults to 5
    seconds.
    </p>
  
  <h3>Example configuration</h3>
    
    <div class="example"><h3>Enabling the cache lock</h3><p><code>
      #<br />
      # Enable the cache lock<br />
      #<br />
      &lt;IfModule mod_cache.c&gt;<br />
      <span class="indent">
        CacheLock on<br />
        CacheLockPath /tmp/mod_cache-lock<br />
        CacheLockMaxAge 5<br />
      </span>
      &lt;/IfModule&gt;
    </code></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="CacheDefaultExpire" id="CacheDefaultExpire">CacheDefaultExpire</a> <a name="cachedefaultexpire" id="cachedefaultexpire">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The default duration to cache a document when no expiry date is specified.</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheDefaultExpire <var>seconds</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheDefaultExpire 3600 (one hour)</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</td></tr>
</table>
    <p>The <code class="directive">CacheDefaultExpire</code> directive specifies a default time,
    in seconds, to cache a document if neither an expiry date nor last-modified date are provided
    with the document. The value specified with the <code class="directive">CacheMaxExpire</code>
    directive does <em>not</em> override this setting.</p>

    <div class="example"><p><code>
      CacheDefaultExpire 86400
    </code></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="CacheDisable" id="CacheDisable">CacheDisable</a> <a name="cachedisable" id="cachedisable">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Disable caching of specified URLs</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheDisable <var> url-string</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</td></tr>
</table>
    <p>The <code class="directive">CacheDisable</code> directive instructs
    <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to <em>not</em> cache urls at or below
    <var>url-string</var>.</p>

    <div class="example"><h3>Example</h3><p><code>
      CacheDisable /local_files
    </code></p></div>

    <p> The <code>no-cache</code> environment variable can be set to 
    disable caching on a finer grained set of resources in versions
    2.2.12 and later.</p>


<h3>See also</h3>
<ul>
<li><a href="../env.html">Environment Variables in Apache</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="CacheEnable" id="CacheEnable">CacheEnable</a> <a name="cacheenable" id="cacheenable">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Enable caching of specified URLs using a specified storage
manager</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheEnable <var>cache_type</var> <var>url-string</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</td></tr>
</table>
    <p>The <code class="directive">CacheEnable</code> directive instructs
    <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to cache urls at or below
    <var>url-string</var>. The cache storage manager is specified with the
    <var>cache_type</var> argument. <var>cache_type</var> <code> mem</code>
    instructs <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to use the memory based storage
    manager implemented by <code class="module"><a href="../mod/mod_mem_cache.html">mod_mem_cache</a></code>. 
    <var>cache_type</var> <code>disk</code> instructs
    <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to use the disk based storage manager
    implemented by <code class="module"><a href="../mod/mod_disk_cache.html">mod_disk_cache</a></code>.
    <var>cache_type</var> <code>fd</code> instructs
    <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to use the file descriptor cache implemented
    by <code class="module"><a href="../mod/mod_mem_cache.html">mod_mem_cache</a></code>.</p>
    <p>In the event that the URL space overlaps between different
    <code class="directive">CacheEnable</code> directives (as in the example below),
    each possible storage manager will be run until the first one that
    actually processes the request. The order in which the storage managers are
    run is determined by the order of the <code class="directive">CacheEnable</code>
    directives in the configuration file.</p>

    <div class="example"><p><code>
      CacheEnable  mem   /manual<br />
      CacheEnable  fd    /images<br />
      CacheEnable  disk  /<br />
    </code></p></div>

    <p>When acting as a forward proxy server, <var>url-string</var> can
    also be used to specify remote sites and proxy protocols which 
    caching should be enabled for.</p>
 
    <div class="example"><p><code>
      # Cache proxied url's<br />
      CacheEnable  disk  /<br /><br />
      # Cache FTP-proxied url's<br />
      CacheEnable  disk  ftp://<br /><br />
      # Cache content from www.apache.org<br />
      CacheEnable  disk  http://www.apache.org/<br />
    </code></p></div>

    <p> The <code>no-cache</code> environment variable can be set to 
    disable caching on a finer grained set of resources in versions
    2.2.12 and later.</p>


<h3>See also</h3>
<ul>
<li><a href="../env.html">Environment Variables in Apache</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="CacheIgnoreCacheControl" id="CacheIgnoreCacheControl">CacheIgnoreCacheControl</a> <a name="cacheignorecachecontrol" id="cacheignorecachecontrol">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore request to not serve cached content to client</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreCacheControl On|Off</code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreCacheControl Off</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</td></tr>
</table>
    <p>Ordinarily, requests containing a Cache-Control: no-cache or
    Pragma: no-cache header value will not be served from the cache.  The
    <code class="directive">CacheIgnoreCacheControl</code> directive allows this
    behavior to be overridden.  <code class="directive">CacheIgnoreCacheControl</code>
    On tells the server to attempt to serve the resource from the cache even
    if the request contains no-cache header values.  Resources requiring
    authorization will <em>never</em> be cached.</p>

    <div class="example"><p><code>
      CacheIgnoreCacheControl On
    </code></p></div>

    <div class="warning"><h3>Warning:</h3>
       This directive will allow serving from the cache even if the client has
       requested that the document not be served from the cache.  This might
       result in stale content being served.
    </div>

<h3>See also</h3>
<ul>
<li><code class="directive"><a href="#cachestoreprivate">CacheStorePrivate</a></code></li>
<li><code class="directive"><a href="#cachestorenostore">CacheStoreNoStore</a></code></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="CacheIgnoreHeaders" id="CacheIgnoreHeaders">CacheIgnoreHeaders</a> <a name="cacheignoreheaders" id="cacheignoreheaders">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Do not store the given HTTP header(s) in the cache.
</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreHeaders <var>header-string</var> [<var>header-string</var>] ...</code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreHeaders None</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</td></tr>
</table>
    <p>According to RFC 2616, hop-by-hop HTTP headers are not stored in
    the cache.  The following HTTP headers are hop-by-hop headers and thus
    do not get stored in the cache in <em>any</em> case regardless of the
    setting of <code class="directive">CacheIgnoreHeaders</code>:</p>

    <ul>
      <li><code>Connection</code></li>
      <li><code>Keep-Alive</code></li>
      <li><code>Proxy-Authenticate</code></li>
      <li><code>Proxy-Authorization</code></li>
      <li><code>TE</code></li>
      <li><code>Trailers</code></li>
      <li><code>Transfer-Encoding</code></li>
      <li><code>Upgrade</code></li>
    </ul>

    <p><code class="directive">CacheIgnoreHeaders</code> specifies additional HTTP
    headers that should not to be stored in the cache.  For example, it makes
    sense in some cases to prevent cookies from being stored in the cache.</p>

    <p><code class="directive">CacheIgnoreHeaders</code> takes a space separated list
    of HTTP headers that should not be stored in the cache. If only hop-by-hop
    headers not should be stored in the cache (the RFC 2616 compliant
    behaviour), <code class="directive">CacheIgnoreHeaders</code> can be set to
    <code>None</code>.</p>

    <div class="example"><h3>Example 1</h3><p><code>
      CacheIgnoreHeaders Set-Cookie
    </code></p></div>

    <div class="example"><h3>Example 2</h3><p><code>
      CacheIgnoreHeaders None
    </code></p></div>

    <div class="warning"><h3>Warning:</h3>
      If headers like <code>Expires</code> which are needed for proper cache
      management are not stored due to a
      <code class="directive">CacheIgnoreHeaders</code> setting, the behaviour of
      mod_cache is undefined.
    </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="CacheIgnoreNoLastMod" id="CacheIgnoreNoLastMod">CacheIgnoreNoLastMod</a> <a name="cacheignorenolastmod" id="cacheignorenolastmod">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore the fact that a response has no Last Modified
header.</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreNoLastMod On|Off</code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreNoLastMod Off</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</td></tr>
</table>
    <p>Ordinarily, documents without a last-modified date are not cached.
    Under some circumstances the last-modified date is removed (during
    <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> processing for example) or not provided
    at all. The <code class="directive">CacheIgnoreNoLastMod</code> directive
    provides a way to specify that documents without last-modified dates
    should be considered for caching, even without a last-modified date.
    If neither a last-modified date nor an expiry date are provided with
    the document then the value specified by the
    <code class="directive">CacheDefaultExpire</code> directive will be used to
    generate an expiration date.</p>

    <div class="example"><p><code>
      CacheIgnoreNoLastMod On
    </code></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="CacheIgnoreQueryString" id="CacheIgnoreQueryString">CacheIgnoreQueryString</a> <a name="cacheignorequerystring" id="cacheignorequerystring">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore query string when caching</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreQueryString On|Off</code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreQueryString Off</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</td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 2.2.6 and later</td></tr>
</table>
    <p>Ordinarily, requests with query string parameters are cached separately
    for each unique query string. This is according to RFC 2616/13.9 done only
    if an expiration time is specified. The 
    <code class="directive">CacheIgnoreQueryString</code> directive tells the cache to
    cache requests even if no expiration time is specified, and to reply with 
    a cached reply even if the query string differs. From a caching point of
    view the request is treated as if having no query string when this 
    directive is enabled.</p>

    <div class="example"><p><code>
      CacheIgnoreQueryString On
    </code></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="CacheIgnoreURLSessionIdentifiers" id="CacheIgnoreURLSessionIdentifiers">CacheIgnoreURLSessionIdentifiers</a> <a name="cacheignoreurlsessionidentifiers" id="cacheignoreurlsessionidentifiers">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore defined session identifiers encoded in the URL when caching
</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreURLSessionIdentifiers <var>identifier</var> [<var>identifier</var>] ...</code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreURLSessionIdentifiers None</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</td></tr>
</table>
    <p>Sometimes applications encode the session identifier into the URL like in the following
    Examples:
    </p>
    <ul>
      <li><code>/someapplication/image.gif;jsessionid=123456789</code></li>
      <li><code>/someapplication/image.gif?PHPSESSIONID=12345678</code></li>
    </ul>
    <p>This causes cachable resources to be stored separately for each session, which
    is often not desired. <code class="directive">CacheIgnoreURLSessionIdentifiers</code> lets
    define a list of identifiers that are removed from the key that is used to identify
    an entity in the cache, such that cachable resources are not stored separately for
    each session.
    </p>
    <p><code>CacheIgnoreURLSessionIdentifiers None</code> clears the list of ignored
    identifiers. Otherwise, each identifier is added to the list.</p>

    <div class="example"><h3>Example 1</h3><p><code>
      CacheIgnoreURLSessionIdentifiers jsessionid
    </code></p></div>

    <div class="example"><h3>Example 2</h3><p><code>
      CacheIgnoreURLSessionIdentifiers None
    </code></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="CacheLastModifiedFactor" id="CacheLastModifiedFactor">CacheLastModifiedFactor</a> <a name="cachelastmodifiedfactor" id="cachelastmodifiedfactor">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The factor used to compute an expiry date based on the
LastModified date.</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLastModifiedFactor <var>float</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLastModifiedFactor 0.1</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</td></tr>
</table>
    <p>In the event that a document does not provide an expiry date but does
    provide a last-modified date, an expiry date can be calculated based on
    the time since the document was last modified. The
    <code class="directive">CacheLastModifiedFactor</code> directive specifies a
    <var>factor</var> to be used in the generation of this expiry date
    according to the following formula:

    <code>expiry-period = time-since-last-modified-date * <var>factor</var>
    expiry-date = current-date + expiry-period</code>

    For example, if the document was last modified 10 hours ago, and
    <var>factor</var> is 0.1 then the expiry-period will be set to
    10*0.1 = 1 hour. If the current time was 3:00pm then the computed
    expiry-date would be 3:00pm + 1hour = 4:00pm.

    If the expiry-period would be longer than that set by
    <code class="directive">CacheMaxExpire</code>, then the latter takes
    precedence.</p>

    <div class="example"><p><code>
      CacheLastModifiedFactor 0.5
    </code></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="CacheLock" id="CacheLock">CacheLock</a> <a name="cachelock" id="cachelock">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Enable the thundering herd lock.</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLock <var>on|off</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLock off</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</td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 2.2.15 and later</td></tr>
</table>
  <p>The <code class="directive">CacheLock</code> directive enables the thundering herd lock
  for the given URL space.</p>
  
  <p>In a minimal configuration the following directive is all that is needed to
  enable the thundering herd lock in the default system temp directory.</p>

  <div class="example"><p><code>
    # Enable chache lock<br />
    CacheLock on<br /><br />
  </code></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="CacheLockMaxAge" id="CacheLockMaxAge">CacheLockMaxAge</a> <a name="cachelockmaxage" id="cachelockmaxage">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Set the maximum possible age of a cache lock.</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLockMaxAge <var>integer</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLockMaxAge 5</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</td></tr>
</table>
  <p>The <code class="directive">CacheLockMaxAge</code> directive specifies the maximum
  age of any cache lock.</p>
  
  <p>A lock older than this value in seconds will be ignored, and the next
  incoming request will be given the opportunity to re-establish the lock.
  This mechanism prevents a slow client taking an excessively long time to refresh
  an entity.</p>
  

</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="CacheLockPath" id="CacheLockPath">CacheLockPath</a> <a name="cachelockpath" id="cachelockpath">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Set the lock path directory.</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLockPath <var>directory</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLockPath /tmp/mod_cache-lock</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</td></tr>
</table>
  <p>The <code class="directive">CacheLockPath</code> directive allows you to specify the
  directory in which the locks are created. By default, the system's temporary
  folder is used. Locks consist of empty files that only exist for stale URLs
  in flight, so is significantly less resource intensive than the traditional
  disk cache.</p>


</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="CacheMaxExpire" id="CacheMaxExpire">CacheMaxExpire</a> <a name="cachemaxexpire" id="cachemaxexpire">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The maximum time in seconds to cache a document</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheMaxExpire <var>seconds</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheMaxExpire 86400 (one day)</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</td></tr>
</table>
    <p>The <code class="directive">CacheMaxExpire</code> directive specifies the maximum number of
    seconds for which cachable HTTP documents will be retained without checking the origin
    server. Thus, documents will be out of date at most this number of seconds. This maximum
    value is enforced even if an expiry date was supplied with the document.</p>

    <div class="example"><p><code>
      CacheMaxExpire 604800
    </code></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="CacheStoreNoStore" id="CacheStoreNoStore">CacheStoreNoStore</a> <a name="cachestorenostore" id="cachestorenostore">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Attempt to cache requests or responses that have been marked as no-store.</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheStoreNoStore On|Off</code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheStoreNoStore Off</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</td></tr>
</table>
    <p>Ordinarily, requests or responses with Cache-Control: no-store header
       values will not be stored in the cache.  The
       <code class="directive">CacheStoreNoCache</code> directive allows this
       behavior to be overridden.  <code class="directive">CacheStoreNoCache</code> On
       tells the server to attempt to cache the resource even if it contains
       no-store header values.  Resources requiring authorization will
       <em>never</em> be cached.</p>

    <div class="example"><p><code>
      CacheStoreNoStore On
    </code></p></div>

    <div class="warning"><h3>Warning:</h3>
       As described in RFC 2616, the no-store directive is intended to
       "prevent the inadvertent release or retention of sensitive information
       (for example, on backup tapes)."  Enabling this option could store
       sensitive information in the cache.  You are hereby warned.
    </div>

<h3>See also</h3>
<ul>
<li><code class="directive"><a href="#cacheignorecachecontrol">CacheIgnoreCacheControl</a></code></li>
<li><code class="directive"><a href="#cachestoreprivate">CacheStorePrivate</a></code></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="CacheStorePrivate" id="CacheStorePrivate">CacheStorePrivate</a> <a name="cachestoreprivate" id="cachestoreprivate">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Attempt to cache responses that the server has marked as private</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheStorePrivate On|Off</code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheStorePrivate Off</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</td></tr>
</table>
    <p>Ordinarily, responses with Cache-Control: private header values will not
       be stored in the cache.  The <code class="directive">CacheStorePrivate</code>
       directive allows this behavior to be overridden.
       <code class="directive">CacheStorePrivate</code> On
       tells the server to attempt to cache the resource even if it contains
       private header values.  Resources requiring authorization will
       <em>never</em> be cached.</p>

    <div class="example"><p><code>
      CacheStorePrivate On
    </code></p></div>

    <div class="warning"><h3>Warning:</h3>
       This directive will allow caching even if the upstream server has
       requested that the resource not be cached.  This directive is only
       ideal for a 'private' cache.
    </div>

<h3>See also</h3>
<ul>
<li><code class="directive"><a href="#cacheignorecachecontrol">CacheIgnoreCacheControl</a></code></li>
<li><code class="directive"><a href="#cachestorenostore">CacheStoreNoStore</a></code></li>
</ul>
</div>
</div>
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