721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard<?xml version="1.0"?>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard<!DOCTYPE modulesynopsis SYSTEM "/style/modulesynopsis.dtd">

e942c741056732f50da2074b36fe59805d370650slive<?xml-stylesheet type="text/xsl" href="/style/manual.en.xsl"?>

d5d794fc2f4cc9ca6d6da17cfa2cdcd8d244bacdnd

d5d794fc2f4cc9ca6d6da17cfa2cdcd8d244bacdnd

7db9f691a00ead175b03335457ca296a33ddf31bnd<modulesynopsis metafile="mod_cache.xml.meta">

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard<name>mod_cache</name>

1e5b300cc68389a18fe3762b1b980b0c86712ba1stoddard<description>RFC 2616 compliant HTTP caching filter.</description>

2f2ba5fb35129a32c3add3a797fa47e28ce3224cnd<status>Extension</status>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard<sourcefile>mod_cache.c</sourcefile>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard<identifier>cache_module</identifier>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard<summary>

b77f6f03c0b6bbc6ecd6e87358f568024733d680colm <note type="warning">This module should be used with care, as when the

b77f6f03c0b6bbc6ecd6e87358f568024733d680colm <directive module="mod_cache">CacheQuickHandler</directive> directive is

b77f6f03c0b6bbc6ecd6e87358f568024733d680colm in its default value of <strong>on</strong>, the <directive

b77f6f03c0b6bbc6ecd6e87358f568024733d680colm module="mod_authz_host">Allow</directive> and <directive

b77f6f03c0b6bbc6ecd6e87358f568024733d680colm module="mod_authz_host">Deny</directive> directives will be circumvented.

b77f6f03c0b6bbc6ecd6e87358f568024733d680colm You should not enable quick handler caching for any content to which you

b77f6f03c0b6bbc6ecd6e87358f568024733d680colm wish to limit access by client host name, address or environment

b77f6f03c0b6bbc6ecd6e87358f568024733d680colm variable.</note>

15f37a157fbbf107658ed82ec30c348a9b6e518end

15f37a157fbbf107658ed82ec30c348a9b6e518end <p><module>mod_cache</module> implements an <a

15f37a157fbbf107658ed82ec30c348a9b6e518end href="http://www.ietf.org/rfc/rfc2616.txt">RFC 2616</a> compliant

15f37a157fbbf107658ed82ec30c348a9b6e518end <strong>HTTP content caching filter</strong>, with support for the caching

1a2bc936a6b4aaf5713c98a230a449fd878d1f06takashi of content negotiated responses containing the Vary header.</p>

3e5f26422e7931e8838f3c844adc4282ef269cdfstoddard

3ec4de296cf8eb31d8a59811b58720efafccf109patrikj <p>RFC 2616 compliant caching provides a mechanism to verify whether

97a9a944b5887e91042b019776c41d5dd74557aferikabele stale or expired content is still fresh, and can represent a significant

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj performance boost when the origin server supports <strong>conditional

3ec4de296cf8eb31d8a59811b58720efafccf109patrikj requests</strong> by honouring the

15f37a157fbbf107658ed82ec30c348a9b6e518end <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.26">If-None-Match</a>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj HTTP request header. Content is only regenerated from scratch when the content

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj has changed, and not when the cached entry expires.</p>

b536777217c919cacb1a6f18eaeff001f3b3f13crbowen

b536777217c919cacb1a6f18eaeff001f3b3f13crbowen <p>As a filter, <module>mod_cache</module> can be placed in front of

88c775368960b64afcdfd93a812f466a109746baerikabele content originating from any handler, including <strong>flat

b536777217c919cacb1a6f18eaeff001f3b3f13crbowen files</strong> (served from a slow disk cached on a fast disk), the output

1e5b300cc68389a18fe3762b1b980b0c86712ba1stoddard of a <strong>CGI script</strong> or <strong>dynamic content

88c775368960b64afcdfd93a812f466a109746baerikabele generator</strong>, or content <strong>proxied from another

1e5b300cc68389a18fe3762b1b980b0c86712ba1stoddard server</strong>.</p>

1e5b300cc68389a18fe3762b1b980b0c86712ba1stoddard

1e5b300cc68389a18fe3762b1b980b0c86712ba1stoddard <p>In the default configuration, <module>mod_cache</module> inserts the

1e5b300cc68389a18fe3762b1b980b0c86712ba1stoddard caching filter as far forward as possible within the filter stack,

1e5b300cc68389a18fe3762b1b980b0c86712ba1stoddard utilising the <strong>quick handler</strong> to bypass all per request

1e5b300cc68389a18fe3762b1b980b0c86712ba1stoddard processing when returning content to the client. In this mode of

1e5b300cc68389a18fe3762b1b980b0c86712ba1stoddard operation, <module>mod_cache</module> may be thought of as a caching

1e5b300cc68389a18fe3762b1b980b0c86712ba1stoddard proxy server bolted to the front of the webserver, while running within

1e5b300cc68389a18fe3762b1b980b0c86712ba1stoddard the webserver itself.</p>

1e5b300cc68389a18fe3762b1b980b0c86712ba1stoddard

1e5b300cc68389a18fe3762b1b980b0c86712ba1stoddard <p>When the quick handler is switched off using the

1e5b300cc68389a18fe3762b1b980b0c86712ba1stoddard <directive module="mod_cache">CacheQuickHandler</directive> directive,

88c775368960b64afcdfd93a812f466a109746baerikabele it becomes possible to insert the <strong>CACHE</strong> filter at a

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard point in the filter stack chosen by the administrator. This provides the

15f37a157fbbf107658ed82ec30c348a9b6e518end opportunity to cache content before that content is personalised by the

15f37a157fbbf107658ed82ec30c348a9b6e518end <module>mod_include</module> filter, or optionally compressed by the

15f37a157fbbf107658ed82ec30c348a9b6e518end <module>mod_deflate</module> filter.</p>

15f37a157fbbf107658ed82ec30c348a9b6e518end

15f37a157fbbf107658ed82ec30c348a9b6e518end <p>Under normal operation, <module>mod_cache</module> will respond to

15f37a157fbbf107658ed82ec30c348a9b6e518end and can be controlled by the

15f37a157fbbf107658ed82ec30c348a9b6e518end <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9">Cache-Control</a>

15f37a157fbbf107658ed82ec30c348a9b6e518end and

15f37a157fbbf107658ed82ec30c348a9b6e518end <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.32">Pragma</a>

1a2bc936a6b4aaf5713c98a230a449fd878d1f06takashi headers sent from a client in a request, or from a

15f37a157fbbf107658ed82ec30c348a9b6e518end server within a response. Under exceptional circumstances,

15f37a157fbbf107658ed82ec30c348a9b6e518end <module>mod_cache</module> can be configured to override these headers

15f37a157fbbf107658ed82ec30c348a9b6e518end and force site specific behaviour, however such behaviour will be limited

15f37a157fbbf107658ed82ec30c348a9b6e518end to this cache only, and will not affect the operation of other caches

15f37a157fbbf107658ed82ec30c348a9b6e518end that may exist between the client and server, and as a result is not

15f37a157fbbf107658ed82ec30c348a9b6e518end recommended unless strictly necessary.</p>

15f37a157fbbf107658ed82ec30c348a9b6e518end

15f37a157fbbf107658ed82ec30c348a9b6e518end <p>RFC 2616 allows for the cache to return stale data while the existing

15f37a157fbbf107658ed82ec30c348a9b6e518end stale entry is refreshed from the origin server, and this is supported

89ebbccde2b87b469b9d6fdb606eeb943c12a824colm by <module>mod_cache</module> when the

89ebbccde2b87b469b9d6fdb606eeb943c12a824colm <directive module="mod_cache">CacheLock</directive> directive is suitably

15f37a157fbbf107658ed82ec30c348a9b6e518end configured. Such responses will contain a

15f37a157fbbf107658ed82ec30c348a9b6e518end <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.46">Warning</a>

15f37a157fbbf107658ed82ec30c348a9b6e518end HTTP header with a 110 response code. RFC 2616 also allows a cache to return

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard stale data when the attempt made to refresh the stale data returns an

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard error 500 or above, and this behaviour is supported by default by

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <module>mod_cache</module>. Such responses will contain a

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.46">Warning</a>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj HTTP header with a 111 response code.</p>

15f37a157fbbf107658ed82ec30c348a9b6e518end

15f37a157fbbf107658ed82ec30c348a9b6e518end <p><module>mod_cache</module> requires the services of one or more

15f37a157fbbf107658ed82ec30c348a9b6e518end storage management modules. One storage management module is included in

15f37a157fbbf107658ed82ec30c348a9b6e518end the base Apache distribution:</p>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <dl>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <dt><module>mod_cache_disk</module></dt>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <dd>Implements a disk based storage manager. Headers and bodies are

15f37a157fbbf107658ed82ec30c348a9b6e518end stored separately on disk, in a directory structure derived from the

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj md5 hash of the cached URL. Multiple content negotiated responses can

1a2bc936a6b4aaf5713c98a230a449fd878d1f06takashi be stored concurrently, however the caching of partial content is not

15f37a157fbbf107658ed82ec30c348a9b6e518end supported by this module. The <program>htcacheclean</program> tool is

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj provided to list cached URLs, remove cached URLs, or to maintain the size

1a2bc936a6b4aaf5713c98a230a449fd878d1f06takashi of the disk cache within size and inode limits.</dd>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj </dl>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj <p>Further details, discussion, and examples, are provided in the

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj <a href="/caching.html">Caching Guide</a>.</p>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj</summary>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj<seealso><a href="/caching.html">Caching Guide</a></seealso>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard

89ebbccde2b87b469b9d6fdb606eeb943c12a824colm<section id="related"><title>Related Modules and Directives</title>

89ebbccde2b87b469b9d6fdb606eeb943c12a824colm <related>

89ebbccde2b87b469b9d6fdb606eeb943c12a824colm <modulelist>

89ebbccde2b87b469b9d6fdb606eeb943c12a824colm <module>mod_cache_disk</module>

89ebbccde2b87b469b9d6fdb606eeb943c12a824colm </modulelist>

89ebbccde2b87b469b9d6fdb606eeb943c12a824colm <directivelist>

89ebbccde2b87b469b9d6fdb606eeb943c12a824colm <directive module="mod_cache_disk">CacheRoot</directive>

89ebbccde2b87b469b9d6fdb606eeb943c12a824colm <directive module="mod_cache_disk">CacheDirLevels</directive>

89ebbccde2b87b469b9d6fdb606eeb943c12a824colm <directive module="mod_cache_disk">CacheDirLength</directive>

89ebbccde2b87b469b9d6fdb606eeb943c12a824colm <directive module="mod_cache_disk">CacheMinFileSize</directive>

89ebbccde2b87b469b9d6fdb606eeb943c12a824colm <directive module="mod_cache_disk">CacheMaxFileSize</directive>

89ebbccde2b87b469b9d6fdb606eeb943c12a824colm </directivelist>

89ebbccde2b87b469b9d6fdb606eeb943c12a824colm </related>

8d36abdf61277cb8ffcecc763c8a86c28f11f8e9covener</section>

8d36abdf61277cb8ffcecc763c8a86c28f11f8e9covener

8d36abdf61277cb8ffcecc763c8a86c28f11f8e9covener<section id="sampleconf"><title>Sample Configuration</title>

15f37a157fbbf107658ed82ec30c348a9b6e518end <example><title>Sample httpd.conf</title>

8d36abdf61277cb8ffcecc763c8a86c28f11f8e9covener #<br />

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard # Sample Cache Configuration<br />

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard #<br />

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard LoadModule cache_module modules/mod_cache.so<br />

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <br />

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj &lt;IfModule mod_cache.c&gt;<br />

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj <indent>

15f37a157fbbf107658ed82ec30c348a9b6e518end LoadModule cache_disk_module modules/mod_cache_disk.so<br />

15f37a157fbbf107658ed82ec30c348a9b6e518end &lt;IfModule mod_cache_disk.c&gt;<br />

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <indent>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard CacheRoot c:/cacheroot<br />

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard CacheEnable disk /<br />

15f37a157fbbf107658ed82ec30c348a9b6e518end CacheDirLevels 5<br />

15f37a157fbbf107658ed82ec30c348a9b6e518end CacheDirLength 3<br />

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard </indent>

15f37a157fbbf107658ed82ec30c348a9b6e518end &lt;/IfModule&gt; <br />

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj <br />

15f37a157fbbf107658ed82ec30c348a9b6e518end # When acting as a proxy, don't cache the list of security updates<br />

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard CacheDisable http://security.update.server/update-list/<br />

8d36abdf61277cb8ffcecc763c8a86c28f11f8e9covener </indent>

8d36abdf61277cb8ffcecc763c8a86c28f11f8e9covener &lt;/IfModule&gt;

8d36abdf61277cb8ffcecc763c8a86c28f11f8e9covener </example>

8d36abdf61277cb8ffcecc763c8a86c28f11f8e9covener</section>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard<section id="thunderingherd"><title>Avoiding the Thundering Herd</title>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <p>When a cached entry becomes stale, <module>mod_cache</module> will submit

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard a conditional request to the backend, which is expected to confirm whether the

15f37a157fbbf107658ed82ec30c348a9b6e518end cached entry is still fresh, and send an updated entity if not.</p>

88c775368960b64afcdfd93a812f466a109746baerikabele <p>A small but finite amount of time exists between the time the cached entity

15f37a157fbbf107658ed82ec30c348a9b6e518end becomes stale, and the time the stale entity is fully refreshed. On a busy

15f37a157fbbf107658ed82ec30c348a9b6e518end server, a significant number of requests might arrive during this time, and

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard cause a <strong>thundering herd</strong> of requests to strike the backend

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard suddenly and unpredicably.</p>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj <p>To keep the thundering herd at bay, the <directive>CacheLock</directive>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj directive can be used to define a directory in which locks are created for

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj URLs <strong>in flight</strong>. The lock is used as a <strong>hint</strong>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj by other requests to either suppress an attempt to cache (someone else has

15f37a157fbbf107658ed82ec30c348a9b6e518end gone to fetch the entity), or to indicate that a stale entry is being refreshed

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard (stale content will be returned in the mean time).

15f37a157fbbf107658ed82ec30c348a9b6e518end </p>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <section>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <title>Initial caching of an entry</title>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <p>When an entity is cached for the first time, a lock will be created for the

15f37a157fbbf107658ed82ec30c348a9b6e518end entity until the response has been fully cached. During the lifetime of the

1b0dce86d7fc8a5aa4c89b05255be26e508c615crpluem lock, the cache will suppress the second and subsequent attempt to cache the

1b0dce86d7fc8a5aa4c89b05255be26e508c615crpluem same entity. While this doesn't hold back the thundering herd, it does stop

1b0dce86d7fc8a5aa4c89b05255be26e508c615crpluem the cache attempting to cache the same entity multiple times simultaneously.

1b0dce86d7fc8a5aa4c89b05255be26e508c615crpluem </p>

1b0dce86d7fc8a5aa4c89b05255be26e508c615crpluem </section>

1b0dce86d7fc8a5aa4c89b05255be26e508c615crpluem <section>

1b0dce86d7fc8a5aa4c89b05255be26e508c615crpluem <title>Refreshment of a stale entry</title>

1b0dce86d7fc8a5aa4c89b05255be26e508c615crpluem <p>When an entity reaches its freshness lifetime and becomes stale, a lock

1b0dce86d7fc8a5aa4c89b05255be26e508c615crpluem will be created for the entity until the response has either been confirmed as

1b0dce86d7fc8a5aa4c89b05255be26e508c615crpluem still fresh, or replaced by the backend. During the lifetime of the lock, the

1b0dce86d7fc8a5aa4c89b05255be26e508c615crpluem second and subsequent incoming request will cause stale data to be returned,

1b0dce86d7fc8a5aa4c89b05255be26e508c615crpluem and the thundering herd is kept at bay.</p>

1b0dce86d7fc8a5aa4c89b05255be26e508c615crpluem </section>

1b0dce86d7fc8a5aa4c89b05255be26e508c615crpluem <section>

1b0dce86d7fc8a5aa4c89b05255be26e508c615crpluem <title>Locks and Cache-Control: no-cache</title>

1b0dce86d7fc8a5aa4c89b05255be26e508c615crpluem <p>Locks are used as a <strong>hint only</strong> to enable the cache to be

1b0dce86d7fc8a5aa4c89b05255be26e508c615crpluem more gentle on backend servers, however the lock can be overridden if necessary.

1b0dce86d7fc8a5aa4c89b05255be26e508c615crpluem If the client sends a request with a Cache-Control header forcing a reload, any

1b0dce86d7fc8a5aa4c89b05255be26e508c615crpluem lock that may be present will be ignored, and the client's request will be

1b0dce86d7fc8a5aa4c89b05255be26e508c615crpluem honored immediately and the cached entry refreshed.</p>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <p>As a further safety mechanism, locks have a configurable maximum age.

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard Once this age has been reached, the lock is removed, and a new request is

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj given the opportunity to create a new lock. This maximum age can be set using

15f37a157fbbf107658ed82ec30c348a9b6e518end the <directive>CacheLockMaxAge</directive> directive, and defaults to 5

88c775368960b64afcdfd93a812f466a109746baerikabele seconds.

15f37a157fbbf107658ed82ec30c348a9b6e518end </p>

15f37a157fbbf107658ed82ec30c348a9b6e518end </section>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <section>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <title>Example configuration</title>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj <example><title>Enabling the cache lock</title>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj #<br />

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj # Enable the cache lock<br />

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj #<br />

15f37a157fbbf107658ed82ec30c348a9b6e518end &lt;IfModule mod_cache.c&gt;<br />

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <indent>

15f37a157fbbf107658ed82ec30c348a9b6e518end CacheLock on<br />

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard CacheLockPath /tmp/mod_cache-lock<br />

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard CacheLockMaxAge 5<br />

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard </indent>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard &lt;/IfModule&gt;

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard </example>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard </section>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj</section>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj

15f37a157fbbf107658ed82ec30c348a9b6e518end<section id="finecontrol"><title>Fine Control with the CACHE Filter</title>

15f37a157fbbf107658ed82ec30c348a9b6e518end <p>Under the default mode of cache operation, the cache runs as a quick handler,

15f37a157fbbf107658ed82ec30c348a9b6e518end short circuiting the majority of server processing and offering the highest

15f37a157fbbf107658ed82ec30c348a9b6e518end cache performance available.</p>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <p>In this mode, the cache <strong>bolts onto</strong> the front of the server,

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj acting as if a free standing RFC 2616 caching proxy had been placed in front of

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj the server.</p>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj <p>While this mode offers the best performance, the administrator may find that

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj under certain circumstances they may want to perform further processing on the

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj request after the request is cached, such as to inject personalisation into the

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj cached page, or to apply authorisation restrictions to the content. Under these

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj circumstances, an administrator is often forced to place independent reverse

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj proxy servers either behind or in front of the caching server to achieve this.</p>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <p>To solve this problem the <directive module="mod_cache">CacheQuickHandler

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard </directive> directive can be set to <strong>off</strong>, and the server will

15f37a157fbbf107658ed82ec30c348a9b6e518end process all phases normally handled by a non-cached request, including the

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <strong>authentication and authorisation</strong> phases.</p>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <p>In addition, the administrator may optionally specify the <strong>precise point

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard within the filter chain</strong> where caching is to take place by adding the

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <strong>CACHE</strong> filter to the output filter chain.</p>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz <p>For example, to cache content before applying compression to the response,

15f37a157fbbf107658ed82ec30c348a9b6e518end place the <strong>CACHE</strong> filter before the <strong>DEFLATE</strong>

15f37a157fbbf107658ed82ec30c348a9b6e518end filter as in the example below:</p>

15f37a157fbbf107658ed82ec30c348a9b6e518end

15f37a157fbbf107658ed82ec30c348a9b6e518end <example>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard # Cache content before optional compression<br />

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard CacheQuickHandler off<br />

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz AddOutputFilterByType CACHE;DEFLATE text/plain<br /><br />

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz </example>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz <p>Another option is to have content cached before personalisation is applied

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz by <module>mod_include</module> (or another content processing filter). In this

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz example templates containing tags understood by

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz <module>mod_include</module> are cached before being parsed:</p>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <example>

15f37a157fbbf107658ed82ec30c348a9b6e518end # Cache content before mod_include and mod_deflate<br />

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard CacheQuickHandler off<br />

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz AddOutputFilterByType CACHE;INCLUDES;DEFLATE text/html<br /><br />

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz </example>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz <p>You may place the <strong>CACHE</strong> filter anywhere you wish within the

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz filter chain. In this example, content is cached after being parsed by

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz <module>mod_include</module>, but before being processed by

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <module>mod_deflate</module>:</p>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz <example>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard # Cache content between mod_include and mod_deflate<br />

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard CacheQuickHandler off<br />

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem AddOutputFilterByType INCLUDES;CACHE;DEFLATE text/html<br /><br />

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem </example>

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem <note type="warning"><title>Warning:</title>If the location of the

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem <strong>CACHE</strong> filter in the filter chain is changed for any reason,

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem you may need to <strong>flush your cache</strong> to ensure that your data

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem served remains consistent. <module>mod_cache</module> is not in a position

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem to enforce this for you.</note>

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem</section>

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem<section id="status"><title>Cache Status and Logging</title>

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem <p>Once <module>mod_cache</module> has made a decision as to whether or not

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem an entity is to be served from cache, the detailed reason for the decision

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem is written to the subprocess environment within the request under the

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem <strong>cache-status</strong> key. This reason can be logged by the

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem <directive module="mod_log_config">LogFormat</directive> directive as

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem follows:</p>

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem <example>

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem LogFormat "%{cache-status}e ..."

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem </example>

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem <p>Based on the caching decision made, the reason is also written to the

fc3182e72cf0679cbf14a95213fbb9a98c3cf597rpluem subprocess environment under one the following three keys, as appropriate:</p>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <dl>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj <dt>cache-hit</dt><dd>The response was served from cache.</dd>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj <dt>cache-revalidate</dt><dd>The response was stale and was successfully

15f37a157fbbf107658ed82ec30c348a9b6e518end revalidated, then served from cache.</dd>

1e5b300cc68389a18fe3762b1b980b0c86712ba1stoddard <dt>cache-miss</dt><dd>The response was served from the upstream server.</dd>

15f37a157fbbf107658ed82ec30c348a9b6e518end </dl>

15f37a157fbbf107658ed82ec30c348a9b6e518end

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <p>This makes it possible to support conditional logging of cached requests

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard as per the following example:</p>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj <example>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj CustomLog cached-requests.log common env=cache-hit<br />

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj CustomLog uncached-requests.log common env=cache-miss<br />

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj CustomLog revalidated-requests.log common env=cache-revalidate<br />

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj </example>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj</section>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj<directivesynopsis>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj<name>CacheEnable</name>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj<description>Enable caching of specified URLs using a specified storage

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpjmanager</description>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj<syntax>CacheEnable <var>cache_type</var> <var>url-string</var></syntax>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj<contextlist><context>server config</context><context>virtual host</context>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj</contextlist>

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj

62e52789bfc10a5fd0a433af77e77c8ebbbed6c2rederpj<usage>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <p>The <directive>CacheEnable</directive> directive instructs

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <module>mod_cache</module> to cache urls at or below

15f37a157fbbf107658ed82ec30c348a9b6e518end <var>url-string</var>. The cache storage manager is specified with the

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <var>cache_type</var> argument. If the <directive>CacheEnable</directive>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard directive is placed inside a <directive type="section">Location</directive>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard directive, the <var>url-string</var> becomes optional.

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard <var>cache_type</var> <code>disk</code> instructs

1e5b300cc68389a18fe3762b1b980b0c86712ba1stoddard <module>mod_cache</module> to use the disk based storage manager

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz implemented by <module>mod_cache_disk</module>.</p>

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz <p>In the event that the URL space overlaps between different

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz <directive>CacheEnable</directive> directives (as in the example below),

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz each possible storage manager will be run until the first one that

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz actually processes the request. The order in which the storage managers are

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz run is determined by the order of the <directive>CacheEnable</directive>

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz directives in the configuration file.</p>

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz <p>When acting as a forward proxy server, <var>url-string</var> can

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz also be used to specify remote sites and proxy protocols which

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz caching should be enabled for.</p>

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz <example>

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz # Cache proxied url's<br />

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz CacheEnable disk /<br /><br />

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz # Cache FTP-proxied url's<br />

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz CacheEnable disk ftp://<br /><br />

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz # Cache content from www.apache.org<br />

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz CacheEnable disk http://www.apache.org/<br />

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz </example>

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz <p>A hostname starting with a <strong>"*"</strong> matches all hostnames with

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz that suffix. A hostname starting with <strong>"."</strong> matches all

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz hostnames containing the domain components that follow.</p>

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz <example>

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz # Match www.apache.org, and fooapache.org<br />

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz CacheEnable disk http://*apache.org/<br />

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz # Match www.apache.org, but not fooapache.org<br />

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz CacheEnable disk http://.apache.org/<br />

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz </example>

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz <p> The <code>no-cache</code> environment variable can be set to

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz disable caching on a finer grained set of resources in versions

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz 2.2.12 and later.</p>

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz</usage>

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz<seealso><a href="/env.html">Environment Variables in Apache</a></seealso>

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz</directivesynopsis>

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz<directivesynopsis>

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz<name>CacheDisable</name>

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz<description>Disable caching of specified URLs</description>

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz<syntax>CacheDisable <var>url-string</var> | <var>on</var></syntax>

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz<contextlist><context>server config</context><context>virtual host</context>

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz</contextlist>

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz<usage>

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz <p>The <directive>CacheDisable</directive> directive instructs

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz <module>mod_cache</module> to <em>not</em> cache urls at or below

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz <var>url-string</var>.</p>

a80dd6ffd7a1484e7f45e4665689bdd84fc97153jerenkrantz

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz <example><title>Example</title>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz CacheDisable /local_files

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz </example>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz <p>If used in a <directive type="section">Location</directive> directive,

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz the path needs to be specified below the Location, or if the word "on"

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz is used, caching for the whole location will be disabled.</p>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz <example><title>Example</title>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz &lt;Location /foo&gt;<br />

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz CacheDisable on<br />

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz &lt;/Location&gt;<br />

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz </example>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz <p> The <code>no-cache</code> environment variable can be set to

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz disable caching on a finer grained set of resources in versions

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz 2.2.12 and later.</p>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz</usage>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz<seealso><a href="/env.html">Environment Variables in Apache</a></seealso>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz</directivesynopsis>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz<directivesynopsis>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz<name>CacheMaxExpire</name>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz<description>The maximum time in seconds to cache a document</description>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz<syntax>CacheMaxExpire <var>seconds</var></syntax>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz<default>CacheMaxExpire 86400 (one day)</default>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz<contextlist><context>server config</context>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz <context>virtual host</context>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz <context>directory</context>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz <context>.htaccess</context>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz</contextlist>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz<usage>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz <p>The <directive>CacheMaxExpire</directive> directive specifies the maximum number of

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz seconds for which cachable HTTP documents will be retained without checking the origin

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz server. Thus, documents will be out of date at most this number of seconds. This maximum

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz value is enforced even if an expiry date was supplied with the document.</p>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz <example>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz CacheMaxExpire 604800

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz </example>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz</usage>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz</directivesynopsis>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz<directivesynopsis>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz<name>CacheMinExpire</name>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz<description>The minimum time in seconds to cache a document</description>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz<syntax>CacheMinExpire <var>seconds</var></syntax>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz<default>CacheMinExpire 0</default>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz<contextlist><context>server config</context>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz <context>virtual host</context>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz <context>directory</context>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz <context>.htaccess</context>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz</contextlist>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz<usage>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz <p>The <directive>CacheMinExpire</directive> directive specifies the minimum number of

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz seconds for which cachable HTTP documents will be retained without checking the origin

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz server. This is only used if no valid expire time was supplied with the document.</p>

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz

5c6cb72bfeee541644cea8177aefce1157571d3bjerenkrantz <example>

721fdd19e2abef2e8dc46eb5c022ef14efe3367estoddard CacheMinExpire 3600

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>CacheDefaultExpire</name>

<description>The default duration to cache a document when no expiry date is specified.</description>

<syntax>CacheDefaultExpire <var>seconds</var></syntax>

<default>CacheDefaultExpire 3600 (one hour)</default>

<contextlist><context>server config</context>

<context>virtual host</context>

<context>directory</context>

<context>.htaccess</context>

</contextlist>

<usage>

<p>The <directive>CacheDefaultExpire</directive> 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 <directive>CacheMaxExpire</directive>

directive does <em>not</em> override this setting.</p>

<example>

CacheDefaultExpire 86400

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>CacheIgnoreNoLastMod</name>

<description>Ignore the fact that a response has no Last Modified

header.</description>

<syntax>CacheIgnoreNoLastMod On|Off</syntax>

<default>CacheIgnoreNoLastMod Off</default>

<contextlist><context>server config</context>

<context>virtual host</context>

<context>directory</context>

<context>.htaccess</context>

</contextlist>

<usage>

<p>Ordinarily, documents without a last-modified date are not cached.

Under some circumstances the last-modified date is removed (during

<module>mod_include</module> processing for example) or not provided

at all. The <directive>CacheIgnoreNoLastMod</directive> 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

<directive>CacheDefaultExpire</directive> directive will be used to

generate an expiration date.</p>

<example>

CacheIgnoreNoLastMod On

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>CacheIgnoreCacheControl</name>

<description>Ignore request to not serve cached content to client</description>

<syntax>CacheIgnoreCacheControl On|Off</syntax>

<default>CacheIgnoreCacheControl Off</default>

<contextlist><context>server config</context><context>virtual host</context>

</contextlist>

<usage>

<p>Ordinarily, requests containing a Cache-Control: no-cache or

Pragma: no-cache header value will not be served from the cache. The

<directive>CacheIgnoreCacheControl</directive> directive allows this

behavior to be overridden. <directive>CacheIgnoreCacheControl On</directive>

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>

<example>

CacheIgnoreCacheControl On

</example>

<note type="warning"><title>Warning:</title>

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.

</note>

</usage>

<seealso><directive module="mod_cache">CacheStorePrivate</directive></seealso>

<seealso><directive module="mod_cache">CacheStoreNoStore</directive></seealso>

</directivesynopsis>

<directivesynopsis>

<name>CacheIgnoreQueryString</name>

<description>Ignore query string when caching</description>

<syntax>CacheIgnoreQueryString On|Off</syntax>

<default>CacheIgnoreQueryString Off</default>

<contextlist><context>server config</context><context>virtual host</context>

</contextlist>

<usage>

<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

<directive>CacheIgnoreQueryString</directive> 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>

<example>

CacheIgnoreQueryString On

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>CacheLastModifiedFactor</name>

<description>The factor used to compute an expiry date based on the

LastModified date.</description>

<syntax>CacheLastModifiedFactor <var>float</var></syntax>

<default>CacheLastModifiedFactor 0.1</default>

<contextlist><context>server config</context>

<context>virtual host</context>

<context>directory</context>

<context>.htaccess</context>

</contextlist>

<usage>

<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

<directive>CacheLastModifiedFactor</directive> 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

<directive>CacheMaxExpire</directive>, then the latter takes

precedence.</p>

<example>

CacheLastModifiedFactor 0.5

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>CacheIgnoreHeaders</name>

<description>Do not store the given HTTP header(s) in the cache.

</description>

<syntax>CacheIgnoreHeaders <var>header-string</var> [<var>header-string</var>] ...</syntax>

<default>CacheIgnoreHeaders None</default>

<contextlist><context>server config</context><context>virtual host</context>

</contextlist>

<usage>

<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 <directive>CacheIgnoreHeaders</directive>:</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><directive>CacheIgnoreHeaders</directive> 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><directive>CacheIgnoreHeaders</directive> takes a space separated list

of HTTP headers that should not be stored in the cache. If only hop-by-hop

headers not should be stored in the cache (the RFC 2616 compliant

behaviour), <directive>CacheIgnoreHeaders</directive> can be set to

<code>None</code>.</p>

<example><title>Example 1</title>

CacheIgnoreHeaders Set-Cookie

</example>

<example><title>Example 2</title>

CacheIgnoreHeaders None

</example>

<note type="warning"><title>Warning:</title>

If headers like <code>Expires</code> which are needed for proper cache

management are not stored due to a

<directive>CacheIgnoreHeaders</directive> setting, the behaviour of

mod_cache is undefined.

</note>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>CacheIgnoreURLSessionIdentifiers</name>

<description>Ignore defined session identifiers encoded in the URL when caching

</description>

<syntax>CacheIgnoreURLSessionIdentifiers <var>identifier</var> [<var>identifier</var>] ...</syntax>

<default>CacheIgnoreURLSessionIdentifiers None</default>

<contextlist><context>server config</context><context>virtual host</context>

</contextlist>

<usage>

<p>Sometimes applications encode the session identifier into the URL like in the following

Examples:

</p>

<ul>

<li><code>/someapplication/image.gif;jsessionid=123456789</code></li>

<li><code>/someapplication/image.gif?PHPSESSIONID=12345678</code></li>

</ul>

<p>This causes cachable resources to be stored separately for each session, which

is often not desired. <directive>CacheIgnoreURLSessionIdentifiers</directive> lets

define a list of identifiers that are removed from the key that is used to identify

an entity in the cache, such that cachable resources are not stored separately for

each session.

</p>

<p><code>CacheIgnoreURLSessionIdentifiers None</code> clears the list of ignored

identifiers. Otherwise, each identifier is added to the list.</p>

<example><title>Example 1</title>

CacheIgnoreURLSessionIdentifiers jsessionid

</example>

<example><title>Example 2</title>

CacheIgnoreURLSessionIdentifiers None

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>CacheStoreExpired</name>

<description>Attempt to cache responses that the server reports as expired</description>

<syntax>CacheStoreExpired On|Off</syntax>

<default>CacheStoreExpired Off</default>

<contextlist><context>server config</context>

<context>virtual host</context>

<context>directory</context>

<context>.htaccess</context>

</contextlist>

<usage>

<p>Since httpd 2.2.4, responses which have already expired are not

stored in the cache. The <directive>CacheStoreExpired</directive>

directive allows this behavior to be overridden.

<directive>CacheStoreExpired</directive> 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>

<example>

CacheStoreExpired On

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>CacheStorePrivate</name>

<description>Attempt to cache responses that the server has marked as private</description>

<syntax>CacheStorePrivate On|Off</syntax>

<default>CacheStorePrivate Off</default>

<contextlist><context>server config</context>

<context>virtual host</context>

<context>directory</context>

<context>.htaccess</context>

</contextlist>

<usage>

<p>Ordinarily, responses with Cache-Control: private header values will not

be stored in the cache. The <directive>CacheStorePrivate</directive>

directive allows this behavior to be overridden.

<directive>CacheStorePrivate</directive> 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>

<example>

CacheStorePrivate On

</example>

<note type="warning"><title>Warning:</title>

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.

</note>

</usage>

<seealso><directive module="mod_cache">CacheIgnoreCacheControl</directive></seealso>

<seealso><directive module="mod_cache">CacheStoreNoStore</directive></seealso>

</directivesynopsis>

<directivesynopsis>

<name>CacheStoreNoStore</name>

<description>Attempt to cache requests or responses that have been marked as no-store.</description>

<syntax>CacheStoreNoStore On|Off</syntax>

<default>CacheStoreNoStore Off</default>

<contextlist><context>server config</context>

<context>virtual host</context>

<context>directory</context>

<context>.htaccess</context>

</contextlist>

<usage>

<p>Ordinarily, requests or responses with Cache-Control: no-store header

values will not be stored in the cache. The

<directive>CacheStoreNoCache</directive> directive allows this

behavior to be overridden. <directive>CacheStoreNoCache</directive> 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>

<example>

CacheStoreNoStore On

</example>

<note type="warning"><title>Warning:</title>

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.

</note>

</usage>

<seealso><directive module="mod_cache">CacheIgnoreCacheControl</directive></seealso>

<seealso><directive module="mod_cache">CacheStorePrivate</directive></seealso>

</directivesynopsis>

<directivesynopsis>

<name>CacheLock</name>

<description>Enable the thundering herd lock.</description>

<syntax>CacheLock <var>on|off</var></syntax>

<default>CacheLock off</default>

<contextlist><context>server config</context><context>virtual host</context>

</contextlist>

<compatibility>Available in Apache 2.2.15 and later</compatibility>

<usage>

<p>The <directive>CacheLock</directive> 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>

<example>

# Enable cache lock<br />

CacheLock on<br /><br />

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>CacheLockPath</name>

<description>Set the lock path directory.</description>

<syntax>CacheLockPath <var>directory</var></syntax>

<default>CacheLockPath /tmp/mod_cache-lock</default>

<contextlist><context>server config</context><context>virtual host</context>

</contextlist>

<usage>

<p>The <directive>CacheLockPath</directive> 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>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>CacheLockMaxAge</name>

<description>Set the maximum possible age of a cache lock.</description>

<syntax>CacheLockMaxAge <var>integer</var></syntax>

<default>CacheLockMaxAge 5</default>

<contextlist><context>server config</context><context>virtual host</context>

</contextlist>

<usage>

<p>The <directive>CacheLockMaxAge</directive> 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>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>CacheQuickHandler</name>

<description>Run the cache from the quick handler.</description>

<syntax>CacheQuickHandler <var>on|off</var></syntax>

<default>CacheQuickHandler on</default>

<contextlist><context>server config</context><context>virtual host</context>

</contextlist>

<usage>

<p>The <directive module="mod_cache">CacheQuickHandler</directive> 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 authorisation.</p>

<example>

# Run cache as a normal handler<br />

CacheQuickHandler off<br /><br />

</example>

<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>

<example>

# Cache content before mod_include and mod_deflate<br />

CacheQuickHandler off<br />

AddOutputFilterByType CACHE;INCLUDES;DEFLATE text/html<br /><br />

</example>

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

apply.</p>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>CacheHeader</name>

<description>Add an X-Cache header to the response.</description>

<syntax>CacheHeader <var>on|off</var></syntax>

<default>CacheHeader off</default>

<contextlist><context>server config</context>

<context>virtual host</context>

<context>directory</context>

<context>.htaccess</context>

</contextlist>

<compatibility>Available in Apache 2.3.9 and later</compatibility>

<usage>

<p>When the <directive module="mod_cache">CacheHeader</directive> 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 <directive module="core">&lt;Directory&gt;</directive>

or <directive module="core">&lt;Location&gt;</directive> 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>

<example>

# Enable the X-Cache header<br />

CacheHeader on<br />

</example>

<example>

X-Cache: HIT from localhost<br />

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>CacheDetailHeader</name>

<description>Add an X-Cache-Detail header to the response.</description>

<syntax>CacheDetailHeader <var>on|off</var></syntax>

<default>CacheDetailHeader off</default>

<contextlist><context>server config</context>

<context>virtual host</context>

<context>directory</context>

<context>.htaccess</context>

</contextlist>

<compatibility>Available in Apache 2.3.9 and later</compatibility>

<usage>

<p>When the <directive module="mod_cache">CacheDetailHeader</directive> 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

<directive module="core">&lt;Directory&gt;</directive> or

<directive module="core">&lt;Location&gt;</directive> 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>

<example>

# Enable the X-Cache-Detail header<br />

CacheDetailHeader on<br />

</example>

<example>

X-Cache-Detail: "conditional cache hit: entity refreshed" from localhost<br />

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>CacheKeyBaseURL</name>

<description>Override the base URL of reverse proxied cache keys.</description>

<syntax>CacheKeyBaseURL <var>URL</var></syntax>

<default>CacheKeyBaseURL http://example.com</default>

<contextlist><context>server config</context>

<context>virtual host</context>

</contextlist>

<compatibility>Available in Apache 2.3.9 and later</compatibility>

<usage>

<p>When the <directive module="mod_cache">CacheKeyBaseURL</directive> 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>

<example>

# Override the base URL of the cache key.<br />

CacheKeyBaseURL http://www.example.com/<br />

</example>

<note type="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.</note>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>CacheStaleOnError</name>

<description>Serve stale content in place of 5xx responses.</description>

<syntax>CacheStaleOnError <var>on|off</var></syntax>

<default>CacheStaleOnError on</default>

<contextlist><context>server config</context>

<context>virtual host</context>

<context>directory</context>

<context>.htaccess</context>

</contextlist>

<compatibility>Available in Apache 2.3.9 and later</compatibility>

<usage>

<p>When the <directive module="mod_cache">CacheStaleOnError</directive> 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>

<example>

# Serve stale data on error.<br />

CacheStaleOnError on<br />

</example>

</usage>

</directivesynopsis>

</modulesynopsis>