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| author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-08 19:09:22 +0000 |
|---|---|---|
| committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-08 19:09:22 +0000 |
| commit | 2faa747e2303ee774a4b4aace961188e950e185a (patch) | |
| tree | 604e79c7481956ce48f458e3546eaf1090b3ffff /docs/manual/mod/mod_cache.html.en | |
| parent | Initial commit. (diff) | |
| download | apache2-2faa747e2303ee774a4b4aace961188e950e185a.tar.xz apache2-2faa747e2303ee774a4b4aace961188e950e185a.zip | |
Adding upstream version 2.4.58.upstream/2.4.58
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'docs/manual/mod/mod_cache.html.en')
| -rw-r--r-- | docs/manual/mod/mod_cache.html.en | 1078 |
1 files changed, 1078 insertions, 0 deletions
diff --git a/docs/manual/mod/mod_cache.html.en b/docs/manual/mod/mod_cache.html.en new file mode 100644 index 0000000..d554c51 --- /dev/null +++ b/docs/manual/mod/mod_cache.html.en @@ -0,0 +1,1078 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head> +<meta content="text/html; charset=UTF-8" http-equiv="Content-Type" /> +<!-- + XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX + This file is generated from xml source: DO NOT EDIT + XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX + --> +<title>mod_cache - Apache HTTP Server Version 2.4</title> +<link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /> +<link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" /> +<link href="../style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /><link rel="stylesheet" type="text/css" href="../style/css/prettify.css" /> +<script src="../style/scripts/prettify.min.js" type="text/javascript"> +</script> + +<link href="../images/favicon.ico" rel="shortcut icon" /></head> +<body> +<div id="page-header"> +<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p> +<p class="apache">Apache HTTP Server Version 2.4</p> +<img alt="" src="../images/feather.png" /></div> +<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div> +<div id="path"> +<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.4</a> > <a href="./">Modules</a></div> +<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>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> +<h3>Summary</h3> + + <div class="warning">This module should be used with care, as when the + <code class="directive"><a href="#cachequickhandler">CacheQuickHandler</a></code> directive is + in its default value of <strong>on</strong>, the <code class="directive"><a href="../mod/mod_access_compat.html#allow">Allow</a></code> and <code class="directive"><a href="../mod/mod_access_compat.html#deny">Deny</a></code> directives will be circumvented. + You should not enable quick handler caching for any content to which you + wish to limit access by client host name, address or environment + variable.</div> + + <p><code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> implements an <a href="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_cache_disk.html">mod_cache_disk</a></code></dt> + <dd>Implements a disk based storage manager. Headers and bodies are + stored separately on disk, in a directory structure derived from the + md5 hash of the cached URL. Multiple content negotiated responses can + be stored concurrently, however the caching of partial content is not + supported by this module. The <code class="program"><a href="../programs/htcacheclean.html">htcacheclean</a></code> tool is + provided to list cached URLs, remove cached URLs, or to maintain the size + of the disk cache within size and inode limits.</dd> + <dt><code class="module"><a href="../mod/mod_cache_socache.html">mod_cache_socache</a></code></dt> + <dd>Implements a shared object cache based storage manager. Headers and + bodies are stored together beneath a single key based on the URL of the + response being cached. Multiple content negotiated responses can + be stored concurrently, however the caching of partial content is not + supported by this module.</dd> + </dl> + + <p>Further details, discussion, and examples, are provided in the + <a href="../caching.html">Caching Guide</a>.</p> +</div> +<div id="quickview"><a href="https://www.apache.org/foundation/contributing.html" class="badge"><img src="https://www.apache.org/images/SupportApache-small.png" alt="Support Apache!" /></a><h3>Topics</h3> +<ul id="topics"> +<li><img alt="" src="../images/down.gif" /> <a href="#related">Related Modules and Directives</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#sampleconf">Sample Configuration</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#thunderingherd">Avoiding the Thundering Herd</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#finecontrol">Fine Control with the CACHE Filter</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#status">Cache Status and Logging</a></li> +</ul><h3 class="directives">Directives</h3> +<ul id="toc"> +<li><img alt="" src="../images/down.gif" /> <a href="#cachedefaultexpire">CacheDefaultExpire</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#cachedetailheader">CacheDetailHeader</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#cachedisable">CacheDisable</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#cacheenable">CacheEnable</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#cacheheader">CacheHeader</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#cacheignorecachecontrol">CacheIgnoreCacheControl</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#cacheignoreheaders">CacheIgnoreHeaders</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#cacheignorenolastmod">CacheIgnoreNoLastMod</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#cacheignorequerystring">CacheIgnoreQueryString</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#cacheignoreurlsessionidentifiers">CacheIgnoreURLSessionIdentifiers</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#cachekeybaseurl">CacheKeyBaseURL</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#cachelastmodifiedfactor">CacheLastModifiedFactor</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#cachelock">CacheLock</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#cachelockmaxage">CacheLockMaxAge</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#cachelockpath">CacheLockPath</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#cachemaxexpire">CacheMaxExpire</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#cacheminexpire">CacheMinExpire</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#cachequickhandler">CacheQuickHandler</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#cachestaleonerror">CacheStaleOnError</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#cachestoreexpired">CacheStoreExpired</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#cachestorenostore">CacheStoreNoStore</a></li> +<li><img alt="" src="../images/down.gif" /> <a href="#cachestoreprivate">CacheStorePrivate</a></li> +</ul> +<h3>Bugfix checklist</h3><ul class="seealso"><li><a href="https://www.apache.org/dist/httpd/CHANGES_2.4">httpd changelog</a></li><li><a href="https://bz.apache.org/bugzilla/buglist.cgi?bug_status=__open__&list_id=144532&product=Apache%20httpd-2&query_format=specific&order=changeddate%20DESC%2Cpriority%2Cbug_severity&component=mod_cache">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2&component=mod_cache">Report a bug</a></li></ul><h3>See also</h3> +<ul class="seealso"> +<li><a href="../caching.html">Caching Guide</a></li> +<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_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><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> + <p>When a cached entry becomes stale, <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> will submit + a conditional request to the backend, which is expected to confirm whether the + cached entry is still fresh, and send an updated entity if not.</p> + <p>A small but finite amount of time exists between the time the cached entity + becomes stale, and the time the stale entity is fully refreshed. On a busy + server, a significant number of requests might arrive during this time, and + cause a <strong>thundering herd</strong> of requests to strike the backend + suddenly and unpredictably.</p> + <p>To keep the thundering herd at bay, the <code class="directive"><a href="#cachelock">CacheLock</a></code> + directive can be used to define a directory in which locks are created for + URLs <strong>in flight</strong>. The lock is used as a <strong>hint</strong> + by other requests to either suppress an attempt to cache (someone else has + gone to fetch the entity), or to indicate that a stale entry is being refreshed + (stale content will be returned in the mean time). + </p> + <h3>Initial caching of an entry</h3> + + <p>When an entity is cached for the first time, a lock will be created for the + entity until the response has been fully cached. During the lifetime of the + lock, the cache will suppress the second and subsequent attempt to cache the + same entity. While this doesn't hold back the thundering herd, it does stop + the cache attempting to cache the same entity multiple times simultaneously. + </p> + + <h3>Refreshment of a stale entry</h3> + + <p>When an entity reaches its freshness lifetime and becomes stale, a lock + will be created for the entity until the response has either been confirmed as + still fresh, or replaced by the backend. During the lifetime of the lock, the + second and subsequent incoming request will cause stale data to be returned, + and the thundering herd is kept at bay.</p> + + <h3>Locks and Cache-Control: no-cache</h3> + + <p>Locks are used as a <strong>hint only</strong> to enable the cache to be + more gentle on backend servers, however the lock can be overridden if necessary. + If the client sends a request with a Cache-Control header forcing a reload, any + lock that may be present will be ignored, and the client's request will be + honored immediately and the cached entry refreshed.</p> + <p>As a further safety mechanism, locks have a configurable maximum age. + Once this age has been reached, the lock is removed, and a new request is + given the opportunity to create a new lock. This maximum age can be set using + the <code class="directive"><a href="#cachelockmaxage">CacheLockMaxAge</a></code> directive, and defaults + to 5 seconds. + </p> + + <h3>Example configuration</h3> + + <div class="example"><h3>Enabling the cache lock</h3><pre class="prettyprint lang-config"># +# Enable the cache lock +# +<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"> +<h2><a name="finecontrol" id="finecontrol">Fine Control with the CACHE Filter</a></h2> + <p>Under the default mode of cache operation, the cache runs as a quick handler, + short circuiting the majority of server processing and offering the highest + cache performance available.</p> + + <p>In this mode, the cache <strong>bolts onto</strong> the front of the server, + acting as if a free standing RFC 2616 caching proxy had been placed in front of + the server.</p> + + <p>While this mode offers the best performance, the administrator may find that + under certain circumstances they may want to perform further processing on the + request after the request is cached, such as to inject personalisation into the + cached page, or to apply authorization restrictions to the content. Under these + circumstances, an administrator is often forced to place independent reverse + proxy servers either behind or in front of the caching server to achieve this.</p> + + <p>To solve this problem the <code class="directive"><a href="#cachequickhandler">CacheQuickHandler</a></code> + directive can be set to <strong>off</strong>, and the server will + process all phases normally handled by a non-cached request, including the + <strong>authentication and authorization</strong> phases.</p> + + <p>In addition, the administrator may optionally specify the <strong>precise point + within the filter chain</strong> where caching is to take place by adding the + <strong>CACHE</strong> filter to the output filter chain.</p> + + <p>For example, to cache content before applying compression to the response, + place the <strong>CACHE</strong> filter before the <strong>DEFLATE</strong> + filter as in the example below:</p> + + <pre class="prettyprint lang-config"># Cache content before optional compression +CacheQuickHandler off +AddOutputFilterByType CACHE;DEFLATE text/plain</pre> + + + <p>Another option is to have content cached before personalisation is applied + by <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> (or another content processing filter). In this + example templates containing tags understood by + <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> are cached before being parsed:</p> + + <pre class="prettyprint lang-config"># Cache content before mod_include and mod_deflate +CacheQuickHandler off +AddOutputFilterByType CACHE;INCLUDES;DEFLATE text/html</pre> + + + <p>You may place the <strong>CACHE</strong> filter anywhere you wish within the + filter chain. In this example, content is cached after being parsed by + <code class="module"><a href="../mod/mod_include.html">mod_include</a></code>, but before being processed by + <code class="module"><a href="../mod/mod_deflate.html">mod_deflate</a></code>:</p> + + <pre class="prettyprint lang-config"># Cache content between mod_include and mod_deflate +CacheQuickHandler off +AddOutputFilterByType INCLUDES;CACHE;DEFLATE text/html</pre> + + + <div class="warning"><h3>Warning:</h3>If the location of the + <strong>CACHE</strong> filter in the filter chain is changed for any reason, + you may need to <strong>flush your cache</strong> to ensure that your data + served remains consistent. <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> is not in a position + to enforce this for you.</div> + +</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="section"> +<h2><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> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The default duration to cache a document when no expiry date is specified.</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheDefaultExpire <var>seconds</var></code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheDefaultExpire 3600 (one hour)</code></td></tr> +<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr> +<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> +<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> +</table> + <p>The <code class="directive">CacheDefaultExpire</code> directive specifies a default time, + in seconds, to cache a document if neither an expiry date nor last-modified date are provided + with the document. The value specified with the <code class="directive"><a href="#cachemaxexpire">CacheMaxExpire</a></code> + directive does <em>not</em> override this setting.</p> + + <pre class="prettyprint lang-config">CacheDefaultExpire 86400</pre> + + +</div> +<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="directive-section"><h2><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">CacheDetailHeader</code> directive + is switched on, an <strong>X-Cache-Detail</strong> header will be added to the response + containing the detailed reason for a particular caching decision.</p> + + <p>It can be useful during development of cached RESTful services to have additional + information about the caching decision written to the response headers, so as to + confirm whether <code>Cache-Control</code> and other headers have been correctly + used by the service and client.</p> + + <p>If the normal handler is used, this directive may appear within a + <code class="directive"><a href="../mod/core.html#directory"><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> | <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> + <p>The <code class="directive">CacheDisable</code> directive instructs + <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to <em>not</em> cache urls at or below + <var>url-string</var>.</p> + + <div class="example"><h3>Example</h3><pre class="prettyprint lang-config">CacheDisable "/local_files"</pre> +</div> + + <p>If used in a <code class="directive"><a href="../mod/core.html#location"><Location></a></code> directive, + the path needs to be specified below the Location, or if the word "on" + is used, caching for the whole location will be disabled.</p> + + <div class="example"><h3>Example</h3><pre class="prettyprint lang-config"><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> + + +<h3>See also</h3> +<ul> +<li><a href="../env.html">Environment Variables in Apache</a></li> +</ul> +</div> +<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="directive-section"><h2><a name="CacheEnable" id="CacheEnable">CacheEnable</a> <a name="cacheenable" id="cacheenable">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Enable caching of specified URLs using a specified storage +manager</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheEnable <var>cache_type</var> [<var>url-string</var>]</code></td></tr> +<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory</td></tr> +<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> +<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> +<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>A url-string of '/' applied to forward proxy content in 2.2 and + earlier.</td></tr> +</table> + <p>The <code class="directive">CacheEnable</code> directive instructs + <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to cache urls at or below + <var>url-string</var>. The cache storage manager is specified with the + <var>cache_type</var> argument. The <code class="directive">CacheEnable</code> + directive can alternatively be placed inside either + <code class="directive"><a href="../mod/core.html#location"><Location></a></code> or + <code class="directive"><a href="../mod/core.html#locationmatch"><LocationMatch></a></code> sections to indicate + the content is cacheable. + <var>cache_type</var> <code>disk</code> instructs + <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to use the disk based storage manager + implemented by <code class="module"><a href="../mod/mod_cache_disk.html">mod_cache_disk</a></code>. <var>cache_type</var> + <code>socache</code> instructs <code class="module"><a href="../mod/mod_cache.html">mod_cache</a></code> to use the + shared object cache based storage manager implemented by + <code class="module"><a href="../mod/mod_cache_socache.html">mod_cache_socache</a></code>.</p> + <p>In the event that the URL space overlaps between different + <code class="directive">CacheEnable</code> directives (as in the example below), + each possible storage manager will be run until the first one that + actually processes the request. The order in which the storage managers are + run is determined by the order of the <code class="directive">CacheEnable</code> + directives in the configuration file. <code class="directive">CacheEnable</code> + directives within <code class="directive"><a href="../mod/core.html#location"><Location></a></code> or + <code class="directive"><a href="../mod/core.html#locationmatch"><LocationMatch></a></code> sections are processed + before globally defined <code class="directive">CacheEnable</code> directives.</p> + + <p>When acting as a forward proxy server, <var>url-string</var> must + minimally begin with a protocol for which caching should be enabled.</p> + + <pre class="prettyprint lang-config"># Cache content (normal handler only) +CacheQuickHandler off +<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> + + +<h3>See also</h3> +<ul> +<li><a href="../env.html">Environment Variables in Apache</a></li> +</ul> +</div> +<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="directive-section"><h2><a name="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">CacheHeader</code> directive + is switched on, an <strong>X-Cache</strong> header will be added to the response + with the cache status of this response. If the normal handler is used, this + directive may appear within a <code class="directive"><a href="../mod/core.html#directory"><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> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore request to not serve cached content to client</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreCacheControl On|Off</code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreCacheControl Off</code></td></tr> +<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> +<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> +<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> +</table> + <p>Ordinarily, requests containing a <code>Cache-Control: no-cache</code> or + Pragma: no-cache header value will not be served from the cache. The + <code class="directive">CacheIgnoreCacheControl</code> directive allows this + behavior to be overridden. <code class="directive">CacheIgnoreCacheControl On</code> + tells the server to attempt to serve the resource from the cache even + if the request contains no-cache header values. Resources requiring + authorization will <em>never</em> be cached.</p> + + <pre class="prettyprint lang-config">CacheIgnoreCacheControl On</pre> + + + <div class="warning"><h3>Warning:</h3> + This directive will allow serving from the cache even if the client has + requested that the document not be served from the cache. This might + result in stale content being served. + </div> + +<h3>See also</h3> +<ul> +<li><code class="directive"><a href="#cachestoreprivate">CacheStorePrivate</a></code></li> +<li><code class="directive"><a href="#cachestorenostore">CacheStoreNoStore</a></code></li> +</ul> +</div> +<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="directive-section"><h2><a name="CacheIgnoreHeaders" id="CacheIgnoreHeaders">CacheIgnoreHeaders</a> <a name="cacheignoreheaders" id="cacheignoreheaders">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Do not store the given HTTP header(s) in the cache. +</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreHeaders <var>header-string</var> [<var>header-string</var>] ...</code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreHeaders None</code></td></tr> +<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> +<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> +<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> +</table> + <p>According to RFC 2616, hop-by-hop HTTP headers are not stored in + the cache. The following HTTP headers are hop-by-hop headers and thus + do not get stored in the cache in <em>any</em> case regardless of the + setting of <code class="directive">CacheIgnoreHeaders</code>:</p> + + <ul> + <li><code>Connection</code></li> + <li><code>Keep-Alive</code></li> + <li><code>Proxy-Authenticate</code></li> + <li><code>Proxy-Authorization</code></li> + <li><code>TE</code></li> + <li><code>Trailers</code></li> + <li><code>Transfer-Encoding</code></li> + <li><code>Upgrade</code></li> + </ul> + + <p><code class="directive">CacheIgnoreHeaders</code> specifies additional HTTP + headers that should not to be stored in the cache. For example, it makes + sense in some cases to prevent cookies from being stored in the cache.</p> + + <p><code class="directive">CacheIgnoreHeaders</code> takes a space separated list + of HTTP headers that should not be stored in the cache. If only hop-by-hop + headers not should be stored in the cache (the RFC 2616 compliant + behaviour), <code class="directive">CacheIgnoreHeaders</code> can be set to + <code>None</code>.</p> + + <div class="example"><h3>Example 1</h3><pre class="prettyprint lang-config">CacheIgnoreHeaders Set-Cookie</pre> +</div> + + <div class="example"><h3>Example 2</h3><pre class="prettyprint lang-config">CacheIgnoreHeaders None</pre> +</div> + + <div class="warning"><h3>Warning:</h3> + If headers like <code>Expires</code> which are needed for proper cache + management are not stored due to a + <code class="directive">CacheIgnoreHeaders</code> setting, the behaviour of + mod_cache is undefined. + </div> + +</div> +<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="directive-section"><h2><a name="CacheIgnoreNoLastMod" id="CacheIgnoreNoLastMod">CacheIgnoreNoLastMod</a> <a name="cacheignorenolastmod" id="cacheignorenolastmod">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore the fact that a response has no Last Modified +header.</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreNoLastMod On|Off</code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreNoLastMod Off</code></td></tr> +<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr> +<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> +<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> +</table> + <p>Ordinarily, documents without a last-modified date are not cached. + Under some circumstances the last-modified date is removed (during + <code class="module"><a href="../mod/mod_include.html">mod_include</a></code> processing for example) or not provided + at all. The <code class="directive">CacheIgnoreNoLastMod</code> directive + provides a way to specify that documents without last-modified dates + should be considered for caching, even without a last-modified date. + If neither a last-modified date nor an expiry date are provided with + the document then the value specified by the + <code class="directive"><a href="#cachedefaultexpire">CacheDefaultExpire</a></code> directive will be used to + generate an expiration date.</p> + + <pre class="prettyprint lang-config">CacheIgnoreNoLastMod On</pre> + + +</div> +<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="directive-section"><h2><a name="CacheIgnoreQueryString" id="CacheIgnoreQueryString">CacheIgnoreQueryString</a> <a name="cacheignorequerystring" id="cacheignorequerystring">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore query string when caching</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreQueryString On|Off</code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreQueryString Off</code></td></tr> +<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> +<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> +<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> +</table> + <p>Ordinarily, requests with query string parameters are cached separately + for each unique query string. This is according to RFC 2616/13.9 done only + if an expiration time is specified. The + <code class="directive">CacheIgnoreQueryString</code> directive tells the cache to + cache requests even if no expiration time is specified, and to reply with + a cached reply even if the query string differs. From a caching point of + view the request is treated as if having no query string when this + directive is enabled.</p> + + <pre class="prettyprint lang-config">CacheIgnoreQueryString On</pre> + + + +</div> +<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="directive-section"><h2><a name="CacheIgnoreURLSessionIdentifiers" id="CacheIgnoreURLSessionIdentifiers">CacheIgnoreURLSessionIdentifiers</a> <a name="cacheignoreurlsessionidentifiers" id="cacheignoreurlsessionidentifiers">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Ignore defined session identifiers encoded in the URL when caching +</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheIgnoreURLSessionIdentifiers <var>identifier</var> [<var>identifier</var>] ...</code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheIgnoreURLSessionIdentifiers None</code></td></tr> +<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> +<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> +<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> +</table> + <p>Sometimes applications encode the session identifier into the URL like in the following + Examples: + </p> + <ul> + <li><code>/someapplication/image.gif;jsessionid=123456789</code></li> + <li><code>/someapplication/image.gif?PHPSESSIONID=12345678</code></li> + </ul> + <p>This causes cacheable resources to be stored separately for each session, which + is often not desired. <code class="directive">CacheIgnoreURLSessionIdentifiers</code> lets + define a list of identifiers that are removed from the key that is used to identify + an entity in the cache, such that cacheable resources are not stored separately for + each session. + </p> + <p><code>CacheIgnoreURLSessionIdentifiers None</code> clears the list of ignored + identifiers. Otherwise, each identifier is added to the list.</p> + + <div class="example"><h3>Example 1</h3><pre class="prettyprint lang-config">CacheIgnoreURLSessionIdentifiers jsessionid</pre> +</div> + + <div class="example"><h3>Example 2</h3><pre class="prettyprint lang-config">CacheIgnoreURLSessionIdentifiers None</pre> +</div> + + +</div> +<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="directive-section"><h2><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#Context">Context:</a></th><td>server config, virtual host</td></tr> +<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> +<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> +<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 2.3.9 and later</td></tr> +</table> + <p>When the <code class="directive">CacheKeyBaseURL</code> directive + is specified, the URL provided will be used as the base URL to calculate + the URL of the cache keys in the reverse proxy configuration. When not specified, + the scheme, hostname and port of the current virtual host is used to construct + the cache key. When a cluster of machines is present, and all cached entries + should be cached beneath the same cache key, a new base URL can be specified + with this directive.</p> + + <pre class="prettyprint lang-config"># Override the base URL of the cache key. +CacheKeyBaseURL "http://www.example.com/"</pre> + + + <div class="warning">Take care when setting this directive. If two separate virtual + hosts are accidentally given the same base URL, entries from one virtual host + will be served to the other.</div> + + +</div> +<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="directive-section"><h2><a name="CacheLastModifiedFactor" id="CacheLastModifiedFactor">CacheLastModifiedFactor</a> <a name="cachelastmodifiedfactor" id="cachelastmodifiedfactor">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The factor used to compute an expiry date based on the +LastModified date.</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLastModifiedFactor <var>float</var></code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLastModifiedFactor 0.1</code></td></tr> +<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr> +<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> +<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> +</table> + <p>In the event that a document does not provide an expiry date but does + provide a last-modified date, an expiry date can be calculated based on + the time since the document was last modified. The + <code class="directive">CacheLastModifiedFactor</code> directive specifies a + <var>factor</var> to be used in the generation of this expiry date + according to the following formula: + + <code>expiry-period = time-since-last-modified-date * <var>factor</var> + expiry-date = current-date + expiry-period</code> + + For example, if the document was last modified 10 hours ago, and + <var>factor</var> is 0.1 then the expiry-period will be set to + 10*0.1 = 1 hour. If the current time was 3:00pm then the computed + expiry-date would be 3:00pm + 1hour = 4:00pm. + + If the expiry-period would be longer than that set by + <code class="directive"><a href="#cachemaxexpire">CacheMaxExpire</a></code>, then the latter takes + precedence.</p> + + <pre class="prettyprint lang-config">CacheLastModifiedFactor 0.5</pre> + + +</div> +<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="directive-section"><h2><a name="CacheLock" id="CacheLock">CacheLock</a> <a name="cachelock" id="cachelock">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Enable the thundering herd lock.</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLock <var>on|off</var></code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLock off</code></td></tr> +<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> +<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> +<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> +<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Available in Apache 2.2.15 and later</td></tr> +</table> + <p>The <code class="directive">CacheLock</code> directive enables the thundering herd lock + for the given URL space.</p> + + <p>In a minimal configuration the following directive is all that is needed to + enable the thundering herd lock in the default system temp directory.</p> + + <pre class="prettyprint lang-config"># Enable cache lock +CacheLock on</pre> + + + +</div> +<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="directive-section"><h2><a name="CacheLockMaxAge" id="CacheLockMaxAge">CacheLockMaxAge</a> <a name="cachelockmaxage" id="cachelockmaxage">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Set the maximum possible age of a cache lock.</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLockMaxAge <var>integer</var></code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLockMaxAge 5</code></td></tr> +<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> +<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> +<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> +</table> + <p>The <code class="directive">CacheLockMaxAge</code> directive specifies the maximum + age of any cache lock.</p> + + <p>A lock older than this value in seconds will be ignored, and the next + incoming request will be given the opportunity to re-establish the lock. + This mechanism prevents a slow client taking an excessively long time to refresh + an entity.</p> + + +</div> +<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="directive-section"><h2><a name="CacheLockPath" id="CacheLockPath">CacheLockPath</a> <a name="cachelockpath" id="cachelockpath">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Set the lock path directory.</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheLockPath <var>directory</var></code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheLockPath /tmp/mod_cache-lock</code></td></tr> +<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> +<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> +<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> +</table> + <p>The <code class="directive">CacheLockPath</code> directive allows you to specify the + directory in which the locks are created. By default, the system's temporary + folder is used. Locks consist of empty files that only exist for stale URLs + in flight, so is significantly less resource intensive than the traditional + disk cache.</p> + + +</div> +<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="directive-section"><h2><a name="CacheMaxExpire" id="CacheMaxExpire">CacheMaxExpire</a> <a name="cachemaxexpire" id="cachemaxexpire">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The maximum time in seconds to cache a document</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheMaxExpire <var>seconds</var></code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheMaxExpire 86400 (one day)</code></td></tr> +<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr> +<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> +<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> +</table> + <p>The <code class="directive">CacheMaxExpire</code> directive specifies the maximum number of + seconds for which cacheable HTTP documents will be retained without checking the origin + server. Thus, documents will be out of date at most this number of seconds. This maximum + value is enforced even if an expiry date was supplied with the document.</p> + + <pre class="prettyprint lang-config">CacheMaxExpire 604800</pre> + + +</div> +<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="directive-section"><h2><a name="CacheMinExpire" id="CacheMinExpire">CacheMinExpire</a> <a name="cacheminexpire" id="cacheminexpire">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>The minimum time in seconds to cache a document</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheMinExpire <var>seconds</var></code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheMinExpire 0</code></td></tr> +<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr> +<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> +<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> +</table> + <p>The <code class="directive">CacheMinExpire</code> directive specifies the minimum number of + seconds for which cacheable HTTP documents will be retained without checking the origin + server. This is only used if no valid expire time was supplied with the document.</p> + + + <pre class="prettyprint lang-config">CacheMinExpire 3600</pre> + + +</div> +<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="directive-section"><h2><a name="CacheQuickHandler" id="CacheQuickHandler">CacheQuickHandler</a> <a name="cachequickhandler" id="cachequickhandler">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Run the cache from the quick handler.</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheQuickHandler <var>on|off</var></code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheQuickHandler on</code></td></tr> +<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host</td></tr> +<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> +<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> +<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>Apache HTTP Server 2.3.3 and later</td></tr> +</table> + <p>The <code class="directive">CacheQuickHandler</code> directive + controls the phase in which the cache is handled.</p> + + <p>In the default enabled configuration, the cache operates within the quick + handler phase. This phase short circuits the majority of server processing, + and represents the most performant mode of operation for a typical server. + The cache <strong>bolts onto</strong> the front of the server, and the + majority of server processing is avoided.</p> + + <p>When disabled, the cache operates as a normal handler, and is subject to + the full set of phases when handling a server request. While this mode is + slower than the default, it allows the cache to be used in cases where full + processing is required, such as when content is subject to authorization.</p> + + <pre class="prettyprint lang-config"># Run cache as a normal handler +CacheQuickHandler off</pre> + + + <p>It is also possible, when the quick handler is disabled, for the + administrator to choose the precise location within the filter chain where + caching is to be performed, by adding the <strong>CACHE</strong> filter to + the chain.</p> + + <pre class="prettyprint lang-config"># Cache content before mod_include and mod_deflate +CacheQuickHandler off +AddOutputFilterByType CACHE;INCLUDES;DEFLATE text/html</pre> + + + <p>If the CACHE filter is specified more than once, the last instance will + apply.</p> + + +</div> +<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="directive-section"><h2><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">CacheStaleOnError</code> directive + is switched on, and when stale data is available in the cache, the cache will + respond to 5xx responses from the backend by returning the stale data instead of + the 5xx response. While the Cache-Control headers sent by clients will be respected, + and the raw 5xx responses returned to the client on request, the 5xx response so + returned to the client will not invalidate the content in the cache.</p> + + <pre class="prettyprint lang-config"># Serve stale data on error. +CacheStaleOnError on</pre> + + + +</div> +<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> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Attempt to cache requests or responses that have been marked as no-store.</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheStoreNoStore On|Off</code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheStoreNoStore Off</code></td></tr> +<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr> +<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> +<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> +</table> + <p>Ordinarily, requests or responses with <code>Cache-Control: no-store</code> header + values will not be stored in the cache. The + <code class="directive">CacheStoreNoStore</code> directive allows this + behavior to be overridden. <code class="directive">CacheStoreNoStore</code> On + tells the server to attempt to cache the resource even if it contains + no-store header values. Resources requiring authorization will + <em>never</em> be cached.</p> + + <pre class="prettyprint lang-config">CacheStoreNoStore On</pre> + + + <div class="warning"><h3>Warning:</h3> + As described in RFC 2616, the no-store directive is intended to + "prevent the inadvertent release or retention of sensitive information + (for example, on backup tapes)." Enabling this option could store + sensitive information in the cache. You are hereby warned. + </div> + +<h3>See also</h3> +<ul> +<li><code class="directive"><a href="#cacheignorecachecontrol">CacheIgnoreCacheControl</a></code></li> +<li><code class="directive"><a href="#cachestoreprivate">CacheStorePrivate</a></code></li> +</ul> +</div> +<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> +<div class="directive-section"><h2><a name="CacheStorePrivate" id="CacheStorePrivate">CacheStorePrivate</a> <a name="cachestoreprivate" id="cachestoreprivate">Directive</a></h2> +<table class="directive"> +<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Attempt to cache responses that the server has marked as private</td></tr> +<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>CacheStorePrivate On|Off</code></td></tr> +<tr><th><a href="directive-dict.html#Default">Default:</a></th><td><code>CacheStorePrivate Off</code></td></tr> +<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr> +<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr> +<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_cache</td></tr> +</table> + <p>Ordinarily, responses with <code>Cache-Control: private</code> header values will not + be stored in the cache. The <code class="directive">CacheStorePrivate</code> + directive allows this behavior to be overridden. + <code class="directive">CacheStorePrivate</code> On + tells the server to attempt to cache the resource even if it contains + private header values. Resources requiring authorization will + <em>never</em> be cached.</p> + + <pre class="prettyprint lang-config">CacheStorePrivate On</pre> + + + <div class="warning"><h3>Warning:</h3> + This directive will allow caching even if the upstream server has + requested that the resource not be cached. This directive is only + ideal for a 'private' cache. + </div> + +<h3>See also</h3> +<ul> +<li><code class="directive"><a href="#cacheignorecachecontrol">CacheIgnoreCacheControl</a></code></li> +<li><code class="directive"><a href="#cachestorenostore">CacheStoreNoStore</a></code></li> +</ul> +</div> +</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 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. 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