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

<name>mod_cache</name>

<description>Content cache keyed to URIs.</description>

<status>Experimental</status>

<sourcefile>mod_cache.c</sourcefile>

<identifier>cache_module</identifier>

<summary>

<note type="warning">

This module is experimental. Documentation is still under development...

</note>

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

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

content cache that can be used to cache either local or proxied content.

<module>mod_cache</module> requires the services of one or more storage

management modules. Two storage management modules are included in

the base Apache distribution:</p>

<dl>

<dt><module>mod_disk_cache</module></dt>

<dd>implements a disk based storage manager.</dd>

<dt><module>mod_mem_cache</module></dt>

<dd>implements a memory based storage manager.

<module>mod_mem_cache</module> can be configured to operate in two

modes: caching open file descriptors or caching objects in heap storage.

<module>mod_mem_cache</module> can be used to cache locally generated content

or to cache backend server content for <module>mod_proxy</module> when

configured using <directive module="mod_proxy">ProxyPass</directive>

(aka <dfn>reverse proxy</dfn>)</dd>

</dl>

<p>Content is stored in and retrieved from the cache using URI based keys. Content with

access protection is not cached.</p>

</summary>

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

<related>

<modulelist>

<module>mod_disk_cache</module>

<module>mod_mem_cache</module>

</modulelist>

<directivelist>

<directive module="mod_disk_cache">CacheRoot</directive>

<directive module="mod_disk_cache">CacheSize</directive>

<directive module="mod_disk_cache">CacheGcInterval</directive>

<directive module="mod_disk_cache">CacheDirLevels</directive>

<directive module="mod_disk_cache">CacheDirLength</directive>

<directive module="mod_disk_cache">CacheExpiryCheck</directive>

<directive module="mod_disk_cache">CacheMinFileSize</directive>

<directive module="mod_disk_cache">CacheMaxFileSize</directive>

<directive module="mod_disk_cache">CacheTimeMargin</directive>

<directive module="mod_disk_cache">CacheGcDaily</directive>

<directive module="mod_disk_cache">CacheGcUnused</directive>

<directive module="mod_disk_cache">CacheGcClean</directive>

<directive module="mod_disk_cache">CacheGcMemUsage</directive>

<directive module="mod_mem_cache">MCacheSize</directive>

<directive module="mod_mem_cache">MCacheMaxObjectCount</directive>

<directive module="mod_mem_cache">MCacheMinObjectSize</directive>

<directive module="mod_mem_cache">MCacheMaxObjectSize</directive>

<directive module="mod_mem_cache">MCacheRemovalAlgorithm</directive>

<directive module="mod_mem_cache">MCacheMaxStreamingBuffer</directive>

</directivelist>

</related>

</section>

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

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

#<br />

# Sample Cache Configuration<br />

#<br />

LoadModule cache_module modules/mod_cache.so<br />

<br />

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

<indent>

#LoadModule disk_cache_module modules/mod_disk_cache.so<br />

&lt;IfModule mod_disk_cache.c&gt;<br />

<indent>

CacheRoot c:/cacheroot<br />

CacheSize 256<br />

CacheEnable disk /<br />

CacheDirLevels 5<br />

CacheDirLength 3<br />

</indent>

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

<br />

LoadModule mem_cache_module modules/mod_mem_cache.so<br />

&lt;IfModule mod_mem_cache.c&gt;<br />

<indent>

CacheEnable mem /<br />

MCacheSize 4096<br />

MCacheMaxObjectCount 100<br />

MCacheMinObjectSize 1<br />

MCacheMaxObjectSize 2048<br />

</indent>

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

</indent>

&lt;/IfModule&gt;

</example>

</section>

<directivesynopsis>

<name>CacheEnable</name>

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

manager</description>

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

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

</contextlist>

<usage>

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

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

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

<var>cache_type</var> argument. <var>cache_type</var> <code> mem</code>

instructs <module>mod_cache</module> to use the memory based storage

manager implemented by <module>mod_mem_cache</module>.

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

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

implemented by <module>mod_disk_cache</module>.

<var>cache_type</var> <code>fd</code> instructs

<module>mod_cache</module> to use the file descriptor cache implemented

by <module>mod_mem_cache</module>.</p>

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

<directive>CacheEnable</directive> 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 <directive>CacheEnable</directive>

directives in the configuration file.</p>

<example>

CacheEnable mem /manual<br />

CacheEnable fd /images<br />

CacheEnable disk /<br />

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>CacheDisable</name>

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

<syntax>CacheDisable <var> url-string</var></syntax>

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

</contextlist>

<usage>

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

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

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

<example><title>Example</title>

CacheDisable /local_files

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>CacheMaxExpire</name>

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

<syntax>CacheMaxExpire <var>seconds</var></syntax>

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

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

</contextlist>

<usage>

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

seconds for which cachable 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>

<example>

CacheMaxExpire 604800

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>CacheDefaultExpire</name>

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

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

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

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

</contextlist>

<usage>

<p>The <directive>CacheDefaultExpire</directive> directive specifies a default time,

in seconds, to cache a document if neither an expiry date nor last-modified date are provided

with the document. The value specified with the <directive>CacheMaxExpire</directive>

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

<example>

CacheDefaultExpire 86400

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>CacheIgnoreNoLastMod</name>

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

header.</description>

<syntax>CacheIgnoreNoLastMod On|Off</syntax>

<default>CacheIgnoreNoLastMod Off</default>

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

</contextlist>

<usage>

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

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

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

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

provides a way to specify that documents without last-modified dates

should be considered for caching, even without a last-modified date.

If neither a last-modified date nor an expiry date are provided with

the document then the value specified by the

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

generate an expiration date.</p>

<example>

CacheIgnoreNoLastMod On

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>CacheIgnoreCacheControl</name>

<description>Ignore the fact that the client requested the content not be

cached.</description>

<syntax>CacheIgnoreCacheControl On|Off</syntax>

<default>CacheIgnoreCacheControl Off</default>

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

</contextlist>

<usage>

<p>Ordinarily, documents with no-cache or no-store header values will not be stored in the cache.

The <directive>CacheIgnoreCacheControl</directive> directive allows this behavior to be overridden.

<directive>CacheIgnoreCacheControl</directive> On tells the server to attempt to cache the document

even if it contains no-cache or no-store header values. Documents requiring authorization will

<em>never</em> be cached.</p>

<example>

CacheIgnoreCacheControl On

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>CacheLastModifiedFactor</name>

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

LastModified date.</description>

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

<default>CacheLastModifiedFactor 0.1</default>

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

</contextlist>

<usage>

<p>In the event that a document does not provide an expiry date but does

provide a last-modified date, an expiry date can be calculated based on

the time since the document was last modified. The

<directive>CacheLastModifiedFactor</directive> directive specifies a

<var>factor</var> to be used in the generation of this expiry date

according to the following formula:

<code>expiry-period = time-since-last-modified-date * <var>factor</var>

expiry-date = current-date + expiry-period</code>

For example, if the document was last modified 10 hours ago, and

<var>factor</var> is 0.1 then the expiry-period will be set to

10*0.1 = 1 hour. If the current time was 3:00pm then the computed

expiry-date would be 3:00pm + 1hour = 4:00pm.

If the expiry-period would be longer than that set by

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

precedence.</p>

<example>

CacheLastModifiedFactor 0.5

</example>

</usage>

</directivesynopsis>

<directivesynopsis>

<name>CacheForceCompletion</name>

<description>Percentage of document served, after which the server

will complete caching the file even if the request is cancelled.</description>

<syntax>CacheForceCompletion <var>Percentage</var></syntax>

<default>CacheForceCompletion 60</default>

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

</contextlist>

<usage>

<p>Ordinarily, if a request is cancelled while the response is being

cached and delivered to the client the processing of the response will

stop and the cache entry will be removed. The

<directive>CacheForceCompletion</directive> directive specifies a

threshold beyond which the document will continue to be cached to

completion, even if the request is cancelled.</p>

<p>The threshold is a percentage specified as a value between

<code>1</code> and <code>100</code>. A value of <code>0</code>

specifies that the default be used. A value of <code>100</code>

will only cache documents that are served in their entirety. A value

between 60 and 90 is recommended.</p>

<example>

CacheForceCompletion 80

</example>

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

This feature is currently <em>not</em> implemented.

</note>

</usage>

</directivesynopsis>

</modulesynopsis>