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<div id="preamble"><h1>Apache Module mod_cache</h1>
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<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>RFC 2616 compliant 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">Module&nbsp;Identifier:</a></th><td>cache_module</td></tr>
<tr><th><a href="module-dict.html#SourceFile">Source&nbsp;File:</a></th><td>mod_cache.c</td></tr></table>
<h3>Summary</h3>

    <div class="warning">This module should be used with care, as when the
    <code class="directive"><a href="#cachequickhandler">CacheQuickHandler</a></code> directive is
    in its default value of <strong>on</strong>, the <code class="directive"><a href="../mod/mod_access_compat.html#allow">Allow</a></code> and <code class="directive"><a href="../mod/mod_access_compat.html#deny">Deny</a></code> directives will be circumvented.
    You should not enable quick handler 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="https://www.rfc-editor.org/rfc/rfc2616">RFC 2616</a> compliant
    <strong>HTTP content caching filter</strong>, with support for the caching
    of content negotiated responses containing the Vary header.</p>

    <p>RFC 2616 compliant caching provides a mechanism to verify whether
    stale or expired content is still fresh, and can represent a significant
    performance boost when the origin server supports <strong>conditional
    requests</strong> by honoring the
    If-None-Match (<a href="https://www.rfc-editor.org/rfc/rfc2616#section-14.26">RFC 2616</a>)
    HTTP request header. Content is only regenerated from scratch when the content
    has changed, and not when the cached entry expires.</p>

    <p>As a filter, <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> can be placed in front of
    content originating from any handler, including <strong>flat
    files</strong> (served from a slow disk cached on a fast disk), the output
    of a <strong>CGI script</strong> or <strong>dynamic content
    generator</strong>, or content <strong>proxied from another
    server</strong>.</p>

    <p>In the default configuration, <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> inserts the
    caching filter as far forward as possible within the filter stack,
    utilising the <strong>quick handler</strong> to bypass all per request
    processing when returning content to the client. In this mode of
    operation, <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> may be thought of as a caching
    proxy server bolted to the front of the webserver, while running within
    the webserver itself.</p>

    <p>When the quick handler is switched off using the
    <code class="directive"><a href="#cachequickhandler">CacheQuickHandler</a></code> directive,
    it becomes possible to insert the <strong>CACHE</strong> filter at a
    point in the filter stack chosen by the administrator. This provides the
    opportunity to cache content before that content is personalised by the
    <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> filter, or optionally compressed by the
    <code class="module"><a href="../mod/mod_deflate.html">mod_deflate</a></code> filter.</p>

    <p>Under normal operation, <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> will respond to
    and can be controlled by the
    Cache-Control (<a href="https://www.rfc-editor.org/rfc/rfc2616#section-14.9">RFC 2616</a>)
    and
    Pragma (<a href="https://www.rfc-editor.org/rfc/rfc2616#section-14.32">RFC 2616</a>)
    headers sent from a client in a request, or from a
    server within a response. Under exceptional circumstances,
    <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> can be configured to override these headers
    and force site specific behavior, however such behavior will be limited
    to this cache only, and will not affect the operation of other caches
    that may exist between the client and server, and as a result is not
    recommended unless strictly necessary.</p>

    <p>RFC 2616 allows for the cache to return stale data while the existing
    stale entry is refreshed from the origin server, and this is supported
    by <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> when the
    <code class="directive"><a href="#cachelock">CacheLock</a></code> directive is suitably
    configured. Such responses will contain a
    Warning (<a href="https://www.rfc-editor.org/rfc/rfc2616#section-14.46">RFC 2616</a>)
    HTTP header with a 110 response code. RFC 2616 also allows a cache to return
    stale data when the attempt made to refresh the stale data returns an
    error 500 or above, and this behavior is supported by default by
    <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code>. Such responses will contain a
    Warning (<a href="https://www.rfc-editor.org/rfc/rfc2616#section-14.46">RFC 2616</a>)
    HTTP header with a 111 response code.</p>

    <p><code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> requires the services of one or more
    storage management modules. The following storage management modules are included in
    the base Apache distribution:</p>
    <dl>
    <dt><code class="module"><a href="../mod/mod_cache_disk.html">mod_cache_disk</a></code></dt>
    <dd>Implements a disk based storage manager. Headers and bodies are
    stored separately on disk, in a directory structure derived from the
    md5 hash of the cached URL. Multiple content negotiated responses can
    be stored concurrently, however the caching of partial content is not
    supported by this module. 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 inode limits.</dd>
    <dt><code class="module"><a href="../mod/mod_cache_socache.html">mod_cache_socache</a></code></dt>
    <dd>Implements a shared object cache based storage manager. Headers and
    bodies are stored together beneath a single key based on the URL of the
    response being cached. Multiple content negotiated responses can
    be stored concurrently, however the caching of partial content is not
    supported by this module.</dd>
    </dl>

    <p>Further details, discussion, and examples, are provided in the
    <a href="../caching.html">Caching Guide</a>.</p>
</div>
<div id="quickview"><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>
<li><img alt="" src="../images/down.gif"> <a href="#finecontrol">Fine Control with the CACHE Filter</a></li>
<li><img alt="" src="../images/down.gif"> <a href="#status">Cache Status and Logging</a></li>
</ul><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="#cachedetailheader">CacheDetailHeader</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="#cacheheader">CacheHeader</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="#cachekeybaseurl">CacheKeyBaseURL</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="#cacheminexpire">CacheMinExpire</a></li>
<li><img alt="" src="../images/down.gif"> <a href="#cachequickhandler">CacheQuickHandler</a></li>
<li><img alt="" src="../images/down.gif"> <a href="#cachestaleonerror">CacheStaleOnError</a></li>
<li><img alt="" src="../images/down.gif"> <a href="#cachestoreexpired">CacheStoreExpired</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>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">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2&amp;component=mod_cache">Report a bug</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 id="related">Related Modules and Directives <a title="Permanent link" href="#related" class="permalink">&para;</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_cache_disk.html">mod_cache_disk</a></code></li><li><code class="module"><a href="../mod/mod_cache_socache.html">mod_cache_socache</a></code></li></ul></td><td><ul><li><code class="directive"><a href="../mod/mod_cache_disk.html#cacheroot">CacheRoot</a></code></li><li><code class="directive"><a href="../mod/mod_cache_disk.html#cachedirlevels">CacheDirLevels</a></code></li><li><code class="directive"><a href="../mod/mod_cache_disk.html#cachedirlength">CacheDirLength</a></code></li><li><code class="directive"><a href="../mod/mod_cache_disk.html#cacheminfilesize">CacheMinFileSize</a></code></li><li><code class="directive"><a href="../mod/mod_cache_disk.html#cachemaxfilesize">CacheMaxFileSize</a></code></li><li><code class="directive"><a href="../mod/mod_cache_socache.html#cachesocache">CacheSocache</a></code></li><li><code class="directive"><a href="../mod/mod_cache_socache.html#cachesocachemaxtime">CacheSocacheMaxTime</a></code></li><li><code class="directive"><a href="../mod/mod_cache_socache.html#cachesocachemintime">CacheSocacheMinTime</a></code></li><li><code class="directive"><a href="../mod/mod_cache_socache.html#cachesocachemaxsize">CacheSocacheMaxSize</a></code></li><li><code class="directive"><a href="../mod/mod_cache_socache.html#cachesocachereadsize">CacheSocacheReadSize</a></code></li><li><code class="directive"><a href="../mod/mod_cache_socache.html#cachesocachereadtime">CacheSocacheReadTime</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 id="sampleconf">Sample Configuration <a title="Permanent link" href="#sampleconf" class="permalink">&para;</a></h2>
    <div class="example"><h3>Sample httpd.conf</h3><pre class="prettyprint lang-config">#
# Sample Cache Configuration
#
LoadModule cache_module modules/mod_cache.so
&lt;IfModule mod_cache.c&gt;
    LoadModule cache_disk_module modules/mod_cache_disk.so
    &lt;IfModule mod_cache_disk.c&gt;
        CacheRoot "c:/cacheroot"
        CacheEnable disk  "/"
        CacheDirLevels 5
        CacheDirLength 3
    &lt;/IfModule&gt;

    # When acting as a proxy, don't cache the list of security updates
    CacheDisable "http://security.update.server/update-list/"
&lt;/IfModule&gt;</pre>
</div>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div>
<div class="section">
<h2 id="thunderingherd">Avoiding the Thundering Herd <a title="Permanent link" href="#thunderingherd" class="permalink">&para;</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 unpredictably.</p>
  <p>To keep the thundering herd at bay, the <code class="directive"><a href="#cachelock">CacheLock</a></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
    honored 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"><a href="#cachelockmaxage">CacheLockMaxAge</a></code> directive, and defaults
    to 5 seconds.
    </p>
  
  <h3>Example configuration</h3>
    
    <div class="example"><h3>Enabling the cache lock</h3><pre class="prettyprint lang-config">#
# Enable the cache lock
#
&lt;IfModule mod_cache.c&gt;
    CacheLock on
    CacheLockPath "/tmp/mod_cache-lock"
    CacheLockMaxAge 5
&lt;/IfModule&gt;</pre>
</div>
  
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div>
<div class="section">
<h2 id="finecontrol">Fine Control with the CACHE Filter <a title="Permanent link" href="#finecontrol" class="permalink">&para;</a></h2>
  <p>Under the default mode of cache operation, the cache runs as a quick handler,
  short circuiting the majority of server processing and offering the highest
  cache performance available.</p>

  <p>In this mode, the cache <strong>bolts onto</strong> the front of the server,
  acting as if a free standing RFC 2616 caching proxy had been placed in front of
  the server.</p>

  <p>While this mode offers the best performance, the administrator may find that
  under certain circumstances they may want to perform further processing on the
  request after the request is cached, such as to inject personalisation into the
  cached page, or to apply authorization restrictions to the content. Under these
  circumstances, an administrator is often forced to place independent reverse
  proxy servers either behind or in front of the caching server to achieve this.</p>

  <p>To solve this problem the <code class="directive"><a href="#cachequickhandler">CacheQuickHandler</a></code>
  directive can be set to <strong>off</strong>, and the server will
  process all phases normally handled by a non-cached request, including the
  <strong>authentication and authorization</strong> phases.</p>

  <p>In addition, the administrator may optionally specify the <strong>precise point
  within the filter chain</strong> where caching is to take place by adding the
  <strong>CACHE</strong> filter to the output filter chain.</p>

  <p>For example, to cache content before applying compression to the response,
  place the <strong>CACHE</strong> filter before the <strong>DEFLATE</strong>
  filter as in the example below:</p>

  <pre class="prettyprint lang-config"># Cache content before optional compression
CacheQuickHandler off
AddOutputFilterByType CACHE;DEFLATE text/plain</pre>


  <p>Another option is to have content cached before personalisation is applied
  by <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> (or another content processing filter). In this
  example templates containing tags understood by
  <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> are cached before being parsed:</p>

  <pre class="prettyprint lang-config"># Cache content before mod_include and mod_deflate
CacheQuickHandler off
AddOutputFilterByType CACHE;INCLUDES;DEFLATE text/html</pre>


  <p>You may place the <strong>CACHE</strong> filter anywhere you wish within the
  filter chain. In this example, content is cached after being parsed by
  <code class="module"><a href="../mod/mod_include.html">mod_include</a></code>, but before being processed by
  <code class="module"><a href="../mod/mod_deflate.html">mod_deflate</a></code>:</p>

  <pre class="prettyprint lang-config"># Cache content between mod_include and mod_deflate
CacheQuickHandler off
AddOutputFilterByType INCLUDES;CACHE;DEFLATE text/html</pre>


  <div class="warning"><h3>Warning:</h3>If the location of the
  <strong>CACHE</strong> filter in the filter chain is changed for any reason,
  you may need to <strong>flush your cache</strong> to ensure that your data
  served remains consistent. <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> is not in a position
  to enforce this for you.</div>

</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div>
<div class="section">
<h2 id="status">Cache Status and Logging <a title="Permanent link" href="#status" class="permalink">&para;</a></h2>
  <p>Once <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> has made a decision as to whether or not
  an entity is to be served from cache, the detailed reason for the decision
  is written to the subprocess environment within the request under the
  <strong>cache-status</strong> key. This reason can be logged by the
  <code class="directive"><a href="../mod/mod_log_config.html#logformat">LogFormat</a></code> directive as
  follows:</p>

  <pre class="prettyprint lang-config">LogFormat "%{cache-status}e ..."</pre>


  <p>Based on the caching decision made, the reason is also written to the
  subprocess environment under one the following four keys, as appropriate:</p>

  <dl>
    <dt>cache-hit</dt><dd>The response was served from cache.</dd>
    <dt>cache-revalidate</dt><dd>The response was stale and was successfully
      revalidated, then served from cache.</dd>
    <dt>cache-miss</dt><dd>The response was served from the upstream server.</dd>
    <dt>cache-invalidate</dt><dd>The cached entity was invalidated by a request
      method other than GET or HEAD.</dd>
  </dl>

  <p>This makes it possible to support conditional logging of cached requests
  as per the following example:</p>

  <pre class="prettyprint lang-config">CustomLog "cached-requests.log" common env=cache-hit
CustomLog "uncached-requests.log" common env=cache-miss
CustomLog "revalidated-requests.log" common env=cache-revalidate
CustomLog "invalidated-requests.log" common env=cache-invalidate</pre>


  <p>For module authors, a hook called <var>cache_status</var> is available,
  allowing modules to respond to the caching outcomes above in customized
  ways.</p>
</div>
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<div class="directive-section"><h2 id="cachedefaultexpire"><span id="CacheDefaultExpire">CacheDefaultExpire</span> Directive <a title="Permanent link" href="#cachedefaultexpire" class="permalink">&para;</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, 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</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"><a href="#cachemaxexpire">CacheMaxExpire</a></code>
    directive does <em>not</em> override this setting.</p>

    <pre class="prettyprint lang-config">CacheDefaultExpire 86400</pre>


</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div>
<div class="directive-section"><h2 id="cachedetailheader"><span id="CacheDetailHeader">CacheDetailHeader</span> Directive <a title="Permanent link" href="#cachedetailheader" class="permalink">&para;</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Add an X-Cache-Detail header to the response.</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheDetailHeader <var>on|off</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheDetailHeader off</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</td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 2.3.9 and later</td></tr>
</table>
  <p>When the <code class="directive">CacheDetailHeader</code> directive
  is switched on, an <strong>X-Cache-Detail</strong> header will be added to the response
  containing the detailed reason for a particular caching decision.</p>

  <p>It can be useful during development of cached RESTful services to have additional
  information about the caching decision written to the response headers, so as to
  confirm whether <code>Cache-Control</code> and other headers have been correctly
  used by the service and client.</p>

  <p>If the normal handler is used, this directive may appear within a
  <code class="directive"><a href="../mod/core.html#directory">&lt;Directory&gt;</a></code> or
  <code class="directive"><a href="../mod/core.html#location">&lt;Location&gt;</a></code> directive. If the quick handler
  is used, this directive must appear within a server or virtual host context, otherwise
  the setting will be ignored.</p>

  <pre class="prettyprint lang-config"># Enable the X-Cache-Detail header
CacheDetailHeader on</pre>


  <div class="example"><p><code>
    X-Cache-Detail: "conditional cache hit: entity refreshed" from localhost<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 id="cachedisable"><span id="CacheDisable">CacheDisable</span> Directive <a title="Permanent link" href="#cachedisable" class="permalink">&para;</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> | <var>on</var></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</td></tr>
</table>
    <div class="note"><p>This directive is only valid in
    <code class="directive"><a href="../mod/core.html#location">&lt;Location&gt;</a></code> and
    <code class="directive"><a href="../mod/mod_proxy.html#proxy">&lt;Proxy&gt;</a></code> sections
    among the per-directory contexts. It is not supported in
    <code class="directive"><a href="../mod/core.html#directory">&lt;Directory&gt;</a></code>,
    <code class="directive"><a href="../mod/core.html#files">&lt;Files&gt;</a></code>, or
    <code class="directive"><a href="../mod/core.html#if">&lt;If&gt;</a></code> sections.</p></div>

    <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><pre class="prettyprint lang-config">CacheDisable "/local_files"</pre>
</div>

    <p>If used in a <code class="directive"><a href="../mod/core.html#location">&lt;Location&gt;</a></code> directive,
    the path needs to be specified below the Location, or if the word "on"
    is used, caching for the whole location will be disabled.</p>

    <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">&lt;Location "/foo"&gt;
    CacheDisable on
&lt;/Location&gt;</pre>
</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 id="cacheenable"><span id="CacheEnable">CacheEnable</span> Directive <a title="Permanent link" href="#cacheenable" class="permalink">&para;</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, directory</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>A url-string of '/' applied to forward proxy content in 2.2 and
 earlier.</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. The <code class="directive">CacheEnable</code>
    directive can alternatively be placed inside either
    <code class="directive"><a href="../mod/core.html#location">&lt;Location&gt;</a></code> or
    <code class="directive"><a href="../mod/core.html#locationmatch">&lt;LocationMatch&gt;</a></code> sections to indicate
    the content is cacheable.
    <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_cache_disk.html">mod_cache_disk</a></code>. <var>cache_type</var>
    <code>socache</code> instructs <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to use the
    shared object cache based storage manager implemented by
    <code class="module"><a href="../mod/mod_cache_socache.html">mod_cache_socache</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. <code class="directive">CacheEnable</code>
    directives within <code class="directive"><a href="../mod/core.html#location">&lt;Location&gt;</a></code> or
    <code class="directive"><a href="../mod/core.html#locationmatch">&lt;LocationMatch&gt;</a></code> sections are processed
    before globally defined <code class="directive">CacheEnable</code> directives.</p>

    <p>When acting as a forward proxy server, <var>url-string</var> must
    minimally begin with a protocol for which caching should be enabled.</p>

    <pre class="prettyprint lang-config"># Cache content (normal handler only)
CacheQuickHandler off
&lt;Location "/foo"&gt;
    CacheEnable disk
&lt;/Location&gt;

# Cache regex (normal handler only)
CacheQuickHandler off
&lt;LocationMatch "foo$"&gt;
    CacheEnable disk
&lt;/LocationMatch&gt;

# Cache all but forward proxy url's (normal or quick handler)
CacheEnable  disk  /

# Cache FTP-proxied url's (normal or quick handler)
CacheEnable  disk  ftp://

# Cache forward proxy content from www.example.org (normal or quick handler)
CacheEnable  disk  http://www.example.org/</pre>


    <p>A hostname starting with a <strong>"*"</strong> matches all hostnames with
    that suffix. A hostname starting with <strong>"."</strong> matches all
    hostnames containing the domain components that follow.</p>

    <pre class="prettyprint lang-config"># Match www.example.org, and fooexample.org
CacheEnable  disk  "http://*example.org/"
# Match www.example.org, but not fooexample.org
CacheEnable  disk  "http://.example.org/"</pre>


    <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 id="cacheheader"><span id="CacheHeader">CacheHeader</span> Directive <a title="Permanent link" href="#cacheheader" class="permalink">&para;</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Add an X-Cache header to the response.</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheHeader <var>on|off</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheHeader off</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</td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 2.3.9 and later</td></tr>
</table>
  <p>When the <code class="directive">CacheHeader</code> directive
  is switched on, an <strong>X-Cache</strong> header will be added to the response
  with the cache status of this response. If the normal handler is used, this
  directive may appear within a <code class="directive"><a href="../mod/core.html#directory">&lt;Directory&gt;</a></code>
  or <code class="directive"><a href="../mod/core.html#location">&lt;Location&gt;</a></code> directive. If the quick
  handler is used, this directive must appear within a server or virtual host
  context, otherwise the setting will be ignored.</p>

  <dl>
    <dt><strong>HIT</strong></dt><dd>The entity was fresh, and was served from
    cache.</dd>
    <dt><strong>REVALIDATE</strong></dt><dd>The entity was stale, was successfully
    revalidated and was served from cache.</dd>
    <dt><strong>MISS</strong></dt><dd>The entity was fetched from the upstream
      server and was not served from cache.</dd>
  </dl>

  <pre class="prettyprint lang-config"># Enable the X-Cache header
CacheHeader on</pre>


  <pre class="prettyprint lang-config">X-Cache: HIT from localhost</pre>



</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div>
<div class="directive-section"><h2 id="cacheignorecachecontrol"><span id="CacheIgnoreCacheControl">CacheIgnoreCacheControl</span> Directive <a title="Permanent link" href="#cacheignorecachecontrol" class="permalink">&para;</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 <code>Cache-Control: no-cache</code> 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 On</code>
    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>

    <pre class="prettyprint lang-config">CacheIgnoreCacheControl On</pre>


    <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 id="cacheignoreheaders"><span id="CacheIgnoreHeaders">CacheIgnoreHeaders</span> Directive <a title="Permanent link" href="#cacheignoreheaders" class="permalink">&para;</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
    behavior), <code class="directive">CacheIgnoreHeaders</code> can be set to
    <code>None</code>.</p>

    <div class="example"><h3>Example 1</h3><pre class="prettyprint lang-config">CacheIgnoreHeaders Set-Cookie</pre>
</div>

    <div class="example"><h3>Example 2</h3><pre class="prettyprint lang-config">CacheIgnoreHeaders None</pre>
</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 behavior 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 id="cacheignorenolastmod"><span id="CacheIgnoreNoLastMod">CacheIgnoreNoLastMod</span> Directive <a title="Permanent link" href="#cacheignorenolastmod" class="permalink">&para;</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, 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</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"><a href="#cachedefaultexpire">CacheDefaultExpire</a></code> directive will be used to
    generate an expiration date.</p>

    <div class="note">More precisely, a 200 OK response is only cached if it includes
    at least one of the <code>Last-Modified</code>, <code>ETag</code>,
    or <code>Expires</code> headers, or a <code>Cache-Control: max-age</code>
    or <code>s-maxage</code> directive. This directive bypasses that
    requirement entirely. When any of those headers are already present,
    this directive has no effect.</div>

    <pre class="prettyprint lang-config">CacheIgnoreNoLastMod On</pre>


</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div>
<div class="directive-section"><h2 id="cacheignorequerystring"><span id="CacheIgnoreQueryString">CacheIgnoreQueryString</span> Directive <a title="Permanent link" href="#cacheignorequerystring" class="permalink">&para;</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>
</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>

    <pre class="prettyprint lang-config">CacheIgnoreQueryString On</pre>



</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div>
<div class="directive-section"><h2 id="cacheignoreurlsessionidentifiers"><span id="CacheIgnoreURLSessionIdentifiers">CacheIgnoreURLSessionIdentifiers</span> Directive <a title="Permanent link" href="#cacheignoreurlsessionidentifiers" class="permalink">&para;</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 cacheable 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 cacheable 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><pre class="prettyprint lang-config">CacheIgnoreURLSessionIdentifiers jsessionid</pre>
</div>

    <div class="example"><h3>Example 2</h3><pre class="prettyprint lang-config">CacheIgnoreURLSessionIdentifiers None</pre>
</div>


</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div>
<div class="directive-section"><h2 id="cachekeybaseurl"><span id="CacheKeyBaseURL">CacheKeyBaseURL</span> Directive <a title="Permanent link" href="#cachekeybaseurl" class="permalink">&para;</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Override the base URL of reverse proxied cache keys.</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheKeyBaseURL <var>URL</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>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 2.3.9 and later</td></tr>
</table>
  <p>When the <code class="directive">CacheKeyBaseURL</code> directive
  is specified, the URL provided will be used as the base URL to calculate
  the URL of the cache keys in the reverse proxy configuration. When not specified,
  the scheme, hostname and port of the current virtual host is used to construct
  the cache key. When a cluster of machines is present, and all cached entries
  should be cached beneath the same cache key, a new base URL can be specified
  with this directive.</p>

  <pre class="prettyprint lang-config"># Override the base URL of the cache key.
CacheKeyBaseURL "http://www.example.com/"</pre>


  <div class="warning">Take care when setting this directive. If two separate virtual
  hosts are accidentally given the same base URL, entries from one virtual host
  will be served to the other.</div>


</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div>
<div class="directive-section"><h2 id="cachelastmodifiedfactor"><span id="CacheLastModifiedFactor">CacheLastModifiedFactor</span> Directive <a title="Permanent link" href="#cachelastmodifiedfactor" class="permalink">&para;</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, 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</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"><a href="#cachemaxexpire">CacheMaxExpire</a></code>, then the latter takes
    precedence.</p>

    <pre class="prettyprint lang-config">CacheLastModifiedFactor 0.5</pre>


</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div>
<div class="directive-section"><h2 id="cachelock"><span id="CacheLock">CacheLock</span> Directive <a title="Permanent link" href="#cachelock" class="permalink">&para;</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>

  <pre class="prettyprint lang-config"># Enable cache lock
CacheLock on</pre>



</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div>
<div class="directive-section"><h2 id="cachelockmaxage"><span id="CacheLockMaxAge">CacheLockMaxAge</span> Directive <a title="Permanent link" href="#cachelockmaxage" class="permalink">&para;</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 id="cachelockpath"><span id="CacheLockPath">CacheLockPath</span> Directive <a title="Permanent link" href="#cachelockpath" class="permalink">&para;</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 id="cachemaxexpire"><span id="CacheMaxExpire">CacheMaxExpire</span> Directive <a title="Permanent link" href="#cachemaxexpire" class="permalink">&para;</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, 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</td></tr>
</table>
    <p>The <code class="directive">CacheMaxExpire</code> directive specifies the maximum number of
    seconds for which cacheable 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>

    <pre class="prettyprint lang-config">CacheMaxExpire 604800</pre>


</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div>
<div class="directive-section"><h2 id="cacheminexpire"><span id="CacheMinExpire">CacheMinExpire</span> Directive <a title="Permanent link" href="#cacheminexpire" class="permalink">&para;</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The minimum time in seconds to cache a document</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheMinExpire <var>seconds</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheMinExpire 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</td></tr>
</table>
    <p>The <code class="directive">CacheMinExpire</code> directive specifies the minimum number of
    seconds for which cacheable HTTP documents will be retained without checking the origin
    server. This is only used if no valid expire time was supplied with the document.</p>


    <pre class="prettyprint lang-config">CacheMinExpire 3600</pre>


</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div>
<div class="directive-section"><h2 id="cachequickhandler"><span id="CacheQuickHandler">CacheQuickHandler</span> Directive <a title="Permanent link" href="#cachequickhandler" class="permalink">&para;</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Run the cache from the quick handler.</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheQuickHandler <var>on|off</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheQuickHandler on</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>Apache HTTP Server 2.3.3 and later</td></tr>
</table>
    <p>The <code class="directive">CacheQuickHandler</code> directive
    controls the phase in which the cache is handled.</p>

    <p>In the default enabled configuration, the cache operates within the quick
    handler phase. This phase short circuits the majority of server processing,
    and represents the most performant mode of operation for a typical server.
    The cache <strong>bolts onto</strong> the front of the server, and the
    majority of server processing is avoided.</p>

    <p>When disabled, the cache operates as a normal handler, and is subject to
    the full set of phases when handling a server request. While this mode is
    slower than the default, it allows the cache to be used in cases where full
    processing is required, such as when content is subject to authorization.</p>

    <pre class="prettyprint lang-config"># Run cache as a normal handler
CacheQuickHandler off</pre>


    <p>It is also possible, when the quick handler is disabled, for the
    administrator to choose the precise location within the filter chain where
    caching is to be performed, by adding the <strong>CACHE</strong> filter to
    the chain.</p>

    <pre class="prettyprint lang-config"># Cache content before mod_include and mod_deflate
CacheQuickHandler off
AddOutputFilterByType CACHE;INCLUDES;DEFLATE text/html</pre>


    <p>If the CACHE filter is specified more than once, the last instance will
    apply.</p>

  
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div>
<div class="directive-section"><h2 id="cachestaleonerror"><span id="CacheStaleOnError">CacheStaleOnError</span> Directive <a title="Permanent link" href="#cachestaleonerror" class="permalink">&para;</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Serve stale content in place of 5xx responses.</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheStaleOnError <var>on|off</var></code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheStaleOnError on</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</td></tr>
<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 2.3.9 and later</td></tr>
</table>
  <p>When the <code class="directive">CacheStaleOnError</code> directive
  is switched on, and when stale data is available in the cache, the cache will
  respond to 5xx responses from the backend by returning the stale data instead of
  the 5xx response. While the Cache-Control headers sent by clients will be respected,
  and the raw 5xx responses returned to the client on request, the 5xx response so
  returned to the client will not invalidate the content in the cache.</p>

  <pre class="prettyprint lang-config"># Serve stale data on error.
CacheStaleOnError on</pre>



</div>
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<div class="directive-section"><h2 id="cachestoreexpired"><span id="CacheStoreExpired">CacheStoreExpired</span> Directive <a title="Permanent link" href="#cachestoreexpired" class="permalink">&para;</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Attempt to cache responses that the server reports as expired</td></tr>
<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheStoreExpired On|Off</code></td></tr>
<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheStoreExpired Off</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</td></tr>
</table>
    <p>Since httpd 2.2.4, responses which have already expired are not
       stored in the cache.  The <code class="directive">CacheStoreExpired</code>
       directive allows this behavior to be overridden.
       <code class="directive">CacheStoreExpired</code> On
       tells the server to attempt to cache the resource if it is stale.
       Subsequent requests would trigger an If-Modified-Since request of
       the origin server, and the response may be fulfilled from cache
       if the backend resource has not changed.</p>

    <pre class="prettyprint lang-config">CacheStoreExpired On</pre>


</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div>
<div class="directive-section"><h2 id="cachestorenostore"><span id="CacheStoreNoStore">CacheStoreNoStore</span> Directive <a title="Permanent link" href="#cachestorenostore" class="permalink">&para;</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, 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</td></tr>
</table>
    <p>Ordinarily, requests or responses with <code>Cache-Control: no-store</code> header
       values will not be stored in the cache.  The
       <code class="directive">CacheStoreNoStore</code> directive allows this
       behavior to be overridden.  <code class="directive">CacheStoreNoStore</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>

    <pre class="prettyprint lang-config">CacheStoreNoStore On</pre>


    <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 id="cachestoreprivate"><span id="CacheStorePrivate">CacheStorePrivate</span> Directive <a title="Permanent link" href="#cachestoreprivate" class="permalink">&para;</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, 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</td></tr>
</table>
    <p>Ordinarily, responses with <code>Cache-Control: private</code> 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>

    <pre class="prettyprint lang-config">CacheStorePrivate On</pre>


    <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>
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