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<div id="page-content">
<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"> en </a> |
+<a href="../fr/mod/mod_cache.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
<a href="../ja/mod/mod_cache.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
<a href="../ko/mod/mod_cache.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
</div>
-<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Content cache keyed to URIs.</td></tr>
+<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 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>
<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_authz_host.html#allow">Allow</a></code> and <code class="directive"><a href="../mod/mod_authz_host.html#deny">Deny</a></code> directives will be circumvented.
+ 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="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. One storage management module is included in
+ 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
+ <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 honouring the
+ <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.26">If-None-Match</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
+ <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9">Cache-Control</a>
+ and
+ <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.32">Pragma</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 behaviour, however such behaviour 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
+ <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.46">Warning</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 behaviour is supported by default by
+ <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code>. Such responses will contain a
+ <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.46">Warning</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_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_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>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="#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="#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>
<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>See also</h3>
<ul class="seealso">
<li><a href="../caching.html">Caching Guide</a></li>
-</ul></div>
+</ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<h2><a name="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></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></ul></td></tr></table>
+ <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><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 />
- <IfModule mod_cache.c><br />
- <span class="indent">
- LoadModule disk_cache_module modules/mod_disk_cache.so<br />
- <IfModule mod_disk_cache.c><br />
- <span class="indent">
- CacheRoot c:/cacheroot<br />
- CacheEnable disk /<br />
- CacheDirLevels 5<br />
- CacheDirLength 3<br />
- </span>
- </IfModule> <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>
- </IfModule>
- </code></p></div>
+ <div class="example"><h3>Sample httpd.conf</h3><pre class="prettyprint lang-config">#
+# Sample Cache Configuration
+#
+LoadModule cache_module modules/mod_cache.so
+<IfModule mod_cache.c>
+ LoadModule cache_disk_module modules/mod_cache_disk.so
+ <IfModule mod_cache_disk.c>
+ CacheRoot c:/cacheroot
+ CacheEnable disk /
+ CacheDirLevels 5
+ CacheDirLength 3
+ </IfModule>
+
+ # When acting as a proxy, don't cache the list of security updates
+ CacheDisable http://security.update.server/update-list/
+</IfModule></pre>
+</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>
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>
+ suddenly and unpredictably.</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>
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>
+ 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
<h3>Example configuration</h3>
- <div class="example"><h3>Enabling the cache lock</h3><p><code>
- #<br />
- # Enable the cache lock<br />
- #<br />
- <IfModule mod_cache.c><br />
- <span class="indent">
- CacheLock on<br />
- CacheLockPath /tmp/mod_cache-lock<br />
- CacheLockMaxAge 5<br />
- </span>
- </IfModule>
- </code></p></div>
+ <div class="example"><h3>Enabling the cache lock</h3><pre class="prettyprint lang-config">#
+# Enable the cache lock
+#
+<IfModule mod_cache.c>
+ CacheLock on
+ CacheLockPath /tmp/mod_cache-lock
+ CacheLockMaxAge 5
+</IfModule></pre>
+</div>
</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="section">
<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 RFC2616 caching proxy had been placed in front of
+ 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 authorisation restrictions to the content. Under these
+ 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
+ <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 authorisation</strong> phases.</p>
+ 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
place the <strong>CACHE</strong> filter before the <strong>DEFLATE</strong>
filter as in the example below:</p>
- <div class="example"><p><code>
- # Cache content before optional compression<br />
- CacheQuickHandler off<br />
- AddOutputFilterByType CACHE;DEFLATE text/plain<br /><br />
- </code></p></div>
+ <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>
- <div class="example"><p><code>
- # Cache content before mod_include and mod_deflate<br />
- CacheQuickHandler off<br />
- AddOutputFilterByType CACHE;INCLUDES;DEFLATE text/html<br /><br />
- </code></p></div>
+ <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>
- <div class="example"><p><code>
- # Cache content between mod_include and mod_deflate<br />
- CacheQuickHandler off<br />
- AddOutputFilterByType INCLUDES;CACHE;DEFLATE text/html<br /><br />
- </code></p></div>
+ <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,
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><a name="status" id="status">Cache Status and Logging</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 customised
+ ways.</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="CacheDefaultExpire" id="CacheDefaultExpire">CacheDefaultExpire</a> <a name="cachedefaultexpire" id="cachedefaultexpire">Directive</a></h2>
<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#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>
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>
+ <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><a name="CacheDetailHeader" id="CacheDetailHeader">CacheDetailHeader</a> <a name="cachedetailheader" id="cachedetailheader">Directive</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"><a href="#cachedetailheader">CacheDetailHeader</a></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"><Directory></a></code> or
+ <code class="directive"><a href="../mod/core.html#location"><Location></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><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#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>
<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>
+ <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">CacheDisable /local_files</pre>
+</div>
+
+ <p>If used in a <code class="directive"><Location></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>
- <p> The <code>no-cache</code> environment variable can be set to
+ <div class="example"><h3>Example</h3><pre class="prettyprint lang-config"><Location /foo>
+ CacheDisable on
+</Location></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>
<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#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.
+ <var>cache_type</var> argument. The <code class="directive">CacheEnable</code>
+ directive can alternatively be placed inside either
+ <code class="directive"><Location></code> or
+ <code class="directive"><LocationMatch></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_disk_cache.html">mod_disk_cache</a></code>.</p>
+ 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.</p>
-
- <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
+ directives in the configuration file. <code class="directive">CacheEnable</code>
+ directives within <code class="directive"><Location></code> or
+ <code class="directive"><LocationMatch></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
+<Location /foo>
+ CacheEnable disk
+</Location>
+
+# Cache regex (normal handler only)
+CacheQuickHandler off
+<LocationMatch foo$>
+ CacheEnable disk
+</LocationMatch>
+
+# 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>
<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="CacheHeader" id="CacheHeader">CacheHeader</a> <a name="cacheheader" id="cacheheader">Directive</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"><a href="#cacheheader">CacheHeader</a></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"><Directory></a></code>
+ or <code class="directive"><a href="../mod/core.html#location"><Location></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><a name="CacheIgnoreCacheControl" id="CacheIgnoreCacheControl">CacheIgnoreCacheControl</a> <a name="cacheignorecachecontrol" id="cacheignorecachecontrol">Directive</a></h2>
<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>
+ if the request contains no-cache header values.</p>
+
+ <pre class="prettyprint lang-config">CacheIgnoreCacheControl On</pre>
- <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
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 1</h3><pre class="prettyprint lang-config">CacheIgnoreHeaders Set-Cookie</pre>
+</div>
- <div class="example"><h3>Example 2</h3><p><code>
- CacheIgnoreHeaders None
- </code></p></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
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#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>
<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>
+ <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>
</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
+ 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
+ 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
+ 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>
+ <pre class="prettyprint lang-config">CacheIgnoreQueryString On</pre>
+
</div>
<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 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><a name="CacheKeyBaseURL" id="CacheKeyBaseURL">CacheKeyBaseURL</a> <a name="cachekeybaseurl" id="cachekeybaseurl">Directive</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#Default">Default:</a></th><td><code>CacheKeyBaseURL http://example.com</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"><a href="#cachekeybaseurl">CacheKeyBaseURL</a></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="example"><h3>Example 2</h3><p><code>
- CacheIgnoreURLSessionIdentifiers None
- </code></p></div>
+ <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>
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#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>
<code class="directive">CacheMaxExpire</code>, then the latter takes
precedence.</p>
- <div class="example"><p><code>
- CacheLastModifiedFactor 0.5
- </code></p></div>
+ <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>
</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>
+ enable the thundering herd lock in the default run-time file directory.</p>
- <div class="example"><p><code>
- # Enable cache lock<br />
- CacheLock on<br /><br />
- </code></p></div>
+ <pre class="prettyprint lang-config"># Enable cache lock
+CacheLock on</pre>
+ <p>Locks consist of empty files that only exist for stale URLs in flight, so this
+ 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="CacheLockMaxAge" id="CacheLockMaxAge">CacheLockMaxAge</a> <a name="cachelockmaxage" id="cachelockmaxage">Directive</a></h2>
</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>
<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#Default">Default:</a></th><td><code>CacheLockPath 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>
-
+ directory in which the locks are created. If <var>directory</var> is not an absolute
+ path, the location specified will be relative to the value of
+ <code class="directive"><a href="../mod/core.html#defaultruntimedir">DefaultRuntimeDir</a></code>.</p>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<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#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>
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>
+ <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>
<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</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>
server. This is only used if no valid expire time was supplied with the document.</p>
- <div class="example"><p><code>
- CacheMinExpire 3600
- </code></p></div>
+ <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>
<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"><a href="#cachequickhandler">CacheQuickHandler</a></code> directive
controls the phase in which the cache is handled.</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 authorisation.</p>
+ 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>
- <div class="example"><p><code>
- # Run cache as a normal handler<br />
- CacheQuickHandler off<br /><br />
- </code></p></div>
<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>
- <div class="example"><p><code>
- # Cache content before mod_include and mod_deflate<br />
- CacheQuickHandler off<br />
- AddOutputFilterByType CACHE;INCLUDES;DEFLATE text/html<br /><br />
- </code></p></div>
+ <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><a name="CacheStaleOnError" id="CacheStaleOnError">CacheStaleOnError</a> <a name="cachestaleonerror" id="cachestaleonerror">Directive</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"><a href="#cachestaleonerror">CacheStaleOnError</a></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>
+<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
+<div class="directive-section"><h2><a name="CacheStoreExpired" id="CacheStoreExpired">CacheStoreExpired</a> <a name="cachestoreexpired" id="cachestoreexpired">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 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><a name="CacheStoreNoStore" id="CacheStoreNoStore">CacheStoreNoStore</a> <a name="cachestorenostore" id="cachestorenostore">Directive</a></h2>
<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#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 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
+ <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>
+ no-store header values.</p>
+
+ <pre class="prettyprint lang-config">CacheStoreNoStore On</pre>
- <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
<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#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>
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>
+ private header values.</p>
+
+ <pre class="prettyprint lang-config">CacheStorePrivate On</pre>
- <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
</div>
<div class="bottomlang">
<p><span>Available Languages: </span><a href="../en/mod/mod_cache.html" title="English"> en </a> |
+<a href="../fr/mod/mod_cache.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
<a href="../ja/mod/mod_cache.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
<a href="../ko/mod/mod_cache.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
-</div><div id="footer">
-<p class="apache">Copyright 2009 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
-<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p></div>
+</div><div class="top"><a href="#page-header"><img src="../images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our <a href="http://httpd.apache.org/lists.html">mailing lists</a>.</div>
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projects / apache / blobdiff