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git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@99326 13f79535-47bb-0310-9956-ffa450edef68
318 lines
13 KiB
XML
318 lines
13 KiB
XML
<?xml version="1.0"?>
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<!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
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<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
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<modulesynopsis metafile="mod_cache.xml.meta">
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<name>mod_cache</name>
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<description>Content cache keyed to URIs.</description>
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<status>Experimental</status>
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<sourcefile>mod_cache.c</sourcefile>
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<identifier>cache_module</identifier>
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<summary>
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<note type="warning">
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This module is experimental. Documentation is still under development...
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</note>
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<p><module>mod_cache</module> implements an <a
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href="http://www.ietf.org/rfc/rfc2616.txt">RFC 2616</a> compliant HTTP
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content cache that can be used to cache either local or proxied content.
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<module>mod_cache</module> requires the services of one or more storage
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management modules. Two storage management modules are included in
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the base Apache distribution:</p>
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<dl>
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<dt><module>mod_disk_cache</module></dt>
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<dd>implements a disk based storage manager.</dd>
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<dt><module>mod_mem_cache</module></dt>
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<dd>implements a memory based storage manager.
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<module>mod_mem_cache</module> can be configured to operate in two
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modes: caching open file descriptors or caching objects in heap storage.
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<module>mod_mem_cache</module> can be used to cache locally generated content
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or to cache backend server content for <module>mod_proxy</module> when
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configured using <directive module="mod_proxy">ProxyPass</directive>
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(aka <dfn>reverse proxy</dfn>)</dd>
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</dl>
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<p>Content is stored in and retrieved from the cache using URI based keys. Content with
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access protection is not cached.</p>
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</summary>
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<section id="related"><title>Related Modules and Directives</title>
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<related>
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<modulelist>
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<module>mod_disk_cache</module>
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<module>mod_mem_cache</module>
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</modulelist>
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<directivelist>
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<directive module="mod_disk_cache">CacheRoot</directive>
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<directive module="mod_disk_cache">CacheSize</directive>
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<directive module="mod_disk_cache">CacheGcInterval</directive>
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<directive module="mod_disk_cache">CacheDirLevels</directive>
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<directive module="mod_disk_cache">CacheDirLength</directive>
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<directive module="mod_disk_cache">CacheExpiryCheck</directive>
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<directive module="mod_disk_cache">CacheMinFileSize</directive>
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<directive module="mod_disk_cache">CacheMaxFileSize</directive>
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<directive module="mod_disk_cache">CacheTimeMargin</directive>
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<directive module="mod_disk_cache">CacheGcDaily</directive>
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<directive module="mod_disk_cache">CacheGcUnused</directive>
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<directive module="mod_disk_cache">CacheGcClean</directive>
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<directive module="mod_disk_cache">CacheGcMemUsage</directive>
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<directive module="mod_mem_cache">MCacheSize</directive>
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<directive module="mod_mem_cache">MCacheMaxObjectCount</directive>
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<directive module="mod_mem_cache">MCacheMinObjectSize</directive>
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<directive module="mod_mem_cache">MCacheMaxObjectSize</directive>
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<directive module="mod_mem_cache">MCacheRemovalAlgorithm</directive>
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<directive module="mod_mem_cache">MCacheMaxStreamingBuffer</directive>
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</directivelist>
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</related>
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</section>
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<section id="sampleconf"><title>Sample Configuration</title>
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<example><title>Sample httpd.conf</title>
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#<br />
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# Sample Cache Configuration<br />
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#<br />
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LoadModule cache_module modules/mod_cache.so<br />
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<br />
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<IfModule mod_cache.c><br />
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<indent>
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#LoadModule disk_cache_module modules/mod_disk_cache.so<br />
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<IfModule mod_disk_cache.c><br />
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<indent>
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CacheRoot c:/cacheroot<br />
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CacheSize 256<br />
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CacheEnable disk /<br />
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CacheDirLevels 5<br />
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CacheDirLength 3<br />
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</indent>
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</IfModule> <br />
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<br />
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LoadModule mem_cache_module modules/mod_mem_cache.so<br />
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<IfModule mod_mem_cache.c><br />
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<indent>
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CacheEnable mem /<br />
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MCacheSize 4096<br />
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MCacheMaxObjectCount 100<br />
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MCacheMinObjectSize 1<br />
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MCacheMaxObjectSize 2048<br />
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</indent>
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</IfModule><br />
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</indent>
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</IfModule>
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</example>
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</section>
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<directivesynopsis>
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<name>CacheEnable</name>
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<description>Enable caching of specified URLs using a specified storage
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manager</description>
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<syntax>CacheEnable <var>cache_type</var> <var>url-string</var></syntax>
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<contextlist><context>server config</context><context>virtual host</context>
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</contextlist>
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<usage>
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<p>The <directive>CacheEnable</directive> directive instructs
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<module>mod_cache</module> to cache urls at or below
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<var>url-string</var>. The cache storage manager is specified with the
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<var>cache_type</var> argument. <var>cache_type</var> <code> mem</code>
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instructs <module>mod_cache</module> to use the memory based storage
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manager implemented by <module>mod_mem_cache</module>.
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<var>cache_type</var> <code>disk</code> instructs
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<module>mod_cache</module> to use the disk based storage manager
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implemented by <module>mod_disk_cache</module>.
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<var>cache_type</var> <code>fd</code> instructs
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<module>mod_cache</module> to use the file descriptor cache implemented
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by <module>mod_mem_cache</module>.</p>
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<p>In the event that the URL space overlaps between different
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<directive>CacheEnable</directive> directives (as in the example below),
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each possible storage manager will be run until the first one that
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actually processes the request. The order in which the storage managers are
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run is determined by the order of the <directive>CacheEnable</directive>
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directives in the configuration file.</p>
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<example>
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CacheEnable mem /manual<br />
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CacheEnable fd /images<br />
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CacheEnable disk /<br />
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</example>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>CacheDisable</name>
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<description>Disable caching of specified URLs</description>
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<syntax>CacheDisable <var> url-string</var></syntax>
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<contextlist><context>server config</context><context>virtual host</context>
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</contextlist>
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<usage>
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<p>The <directive>CacheDisable</directive> directive instructs
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<module>mod_cache</module> to <em>not</em> cache urls at or below
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<var>url-string</var>.</p>
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<example><title>Example</title>
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CacheDisable /local_files
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</example>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>CacheMaxExpire</name>
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<description>The maximum time in seconds to cache a document</description>
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<syntax>CacheMaxExpire <var>seconds</var></syntax>
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<default>CacheMaxExpire 86400 (one day)</default>
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<contextlist><context>server config</context><context>virtual host</context>
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</contextlist>
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<usage>
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<p>The <directive>CacheMaxExpire</directive> directive specifies the maximum number of
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seconds for which cachable HTTP documents will be retained without checking the origin
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server. Thus, documents will be out of date at most this number of seconds. This maximum
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value is enforced even if an expiry date was supplied with the document.</p>
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<example>
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CacheMaxExpire 604800
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</example>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>CacheDefaultExpire</name>
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<description>The default duration to cache a document when no expiry date is specified.</description>
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<syntax>CacheDefaultExpire <var>seconds</var></syntax>
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<default>CacheDefaultExpire 3600 (one hour)</default>
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<contextlist><context>server config</context><context>virtual host</context>
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</contextlist>
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<usage>
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<p>The <directive>CacheDefaultExpire</directive> directive specifies a default time,
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in seconds, to cache a document if neither an expiry date nor last-modified date are provided
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with the document. The value specified with the <directive>CacheMaxExpire</directive>
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directive does <em>not</em> override this setting.</p>
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<example>
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CacheDefaultExpire 86400
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</example>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>CacheIgnoreNoLastMod</name>
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<description>Ignore the fact that a response has no Last Modified
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header.</description>
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<syntax>CacheIgnoreNoLastMod On|Off</syntax>
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<default>CacheIgnoreNoLastMod Off</default>
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<contextlist><context>server config</context><context>virtual host</context>
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</contextlist>
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<usage>
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<p>Ordinarily, documents without a last-modified date are not cached.
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Under some circumstances the last-modified date is removed (during
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<module>mod_include</module> processing for example) or not provided
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at all. The <directive>CacheIgnoreNoLastMod</directive> directive
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provides a way to specify that documents without last-modified dates
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should be considered for caching, even without a last-modified date.
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If neither a last-modified date nor an expiry date are provided with
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the document then the value specified by the
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<directive>CacheDefaultExpire</directive> directive will be used to
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generate an expiration date.</p>
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<example>
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CacheIgnoreNoLastMod On
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</example>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>CacheIgnoreCacheControl</name>
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<description>Ignore the fact that the client requested the content not be
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cached.</description>
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<syntax>CacheIgnoreCacheControl On|Off</syntax>
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<default>CacheIgnoreCacheControl Off</default>
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<contextlist><context>server config</context><context>virtual host</context>
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</contextlist>
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<usage>
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<p>Ordinarily, documents with no-cache or no-store header values will not be stored in the cache.
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The <directive>CacheIgnoreCacheControl</directive> directive allows this behavior to be overridden.
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<directive>CacheIgnoreCacheControl</directive> On tells the server to attempt to cache the document
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even if it contains no-cache or no-store header values. Documents requiring authorization will
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<em>never</em> be cached.</p>
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<example>
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CacheIgnoreCacheControl On
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</example>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>CacheLastModifiedFactor</name>
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<description>The factor used to compute an expiry date based on the
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LastModified date.</description>
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<syntax>CacheLastModifiedFactor <var>float</var></syntax>
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<default>CacheLastModifiedFactor 0.1</default>
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<contextlist><context>server config</context><context>virtual host</context>
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</contextlist>
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<usage>
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<p>In the event that a document does not provide an expiry date but does
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provide a last-modified date, an expiry date can be calculated based on
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the time since the document was last modified. The
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<directive>CacheLastModifiedFactor</directive> directive specifies a
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<var>factor</var> to be used in the generation of this expiry date
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according to the following formula:
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<code>expiry-period = time-since-last-modified-date * <var>factor</var>
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expiry-date = current-date + expiry-period</code>
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For example, if the document was last modified 10 hours ago, and
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<var>factor</var> is 0.1 then the expiry-period will be set to
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10*0.1 = 1 hour. If the current time was 3:00pm then the computed
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expiry-date would be 3:00pm + 1hour = 4:00pm.
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If the expiry-period would be longer than that set by
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<directive>CacheMaxExpire</directive>, then the latter takes
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precedence.</p>
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<example>
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CacheLastModifiedFactor 0.5
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</example>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>CacheForceCompletion</name>
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<description>Percentage of document served, after which the server
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will complete caching the file even if the request is cancelled.</description>
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<syntax>CacheForceCompletion <var>Percentage</var></syntax>
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<default>CacheForceCompletion 60</default>
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<contextlist><context>server config</context><context>virtual host</context>
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</contextlist>
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<usage>
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<p>Ordinarily, if a request is cancelled while the response is being
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cached and delivered to the client the processing of the response will
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stop and the cache entry will be removed. The
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<directive>CacheForceCompletion</directive> directive specifies a
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threshold beyond which the document will continue to be cached to
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completion, even if the request is cancelled.</p>
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<p>The threshold is a percentage specified as a value between
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<code>1</code> and <code>100</code>. A value of <code>0</code>
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specifies that the default be used. A value of <code>100</code>
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will only cache documents that are served in their entirety. A value
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between 60 and 90 is recommended.</p>
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<example>
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CacheForceCompletion 80
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</example>
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<note type="warning"><title>Note:</title>
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This feature is currently <em>not</em> implemented.
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</note>
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</usage>
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</directivesynopsis>
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</modulesynopsis>
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