the base Apache distribution:</p>
<dl>
<dt><module>mod_disk_cache</module></dt>
- <dd>implements a disk based storage manager for use with
- <module>mod_proxy</module></dd>
+ <dd>implements a disk based storage manager.</dd>
<dt><module>mod_mem_cache</module></dt>
- <dd>implements an in-memory based storage manager.
+ <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> is most useful when used to cache
- locally generated content or to cache backend server content for
- <module>mod_proxy</module> configured for <directive module="mod_proxy"
- >ProxyPass</directive> (aka <dfn>reverse proxy</dfn>)</dd>
+ <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 stored and retrived keyed to the URL. Content with
- access protections is not cached.</p>
+ <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>
LoadModule mem_cache_module modules/mod_mem_cache.so<br />
<IfModule mod_mem_cache.c><br />
<indent>
- MCacheEnable mem /<br />
+ CacheEnable mem /<br />
MCacheSize 4096<br />
MCacheMaxObjectCount 100<br />
MCacheMinObjectSize 1<br />
<directivesynopsis>
<name>CacheEnable</name>
-<description>Enable caching specified URLs in a specified storage
+<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>
<usage>
<p>The <directive>CacheEnable</directive> directive instructs
<module>mod_cache</module> to cache urls at or below
- <var>url-string</var>. The cache store is specified with the
- <var>cache_type</var> argument. <var>cache_type</var> <code>mem</code>
- instructs <module>mod_cache</module> to use the in-memory cache storage
- manager implemented by <module>mod_mem_cache</module>.
+ <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 cache storage manager implemented
- by <module>mod_disk_cache</module>.</p>
+ <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 disk /<br />
CacheEnable mem /manual<br />
CacheEnable fd /images<br />
+ CacheEnable disk /<br />
</example>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>CacheDisable</name>
-<description>Disable caching of specified URLs by specified storage
-manager</description>
-<syntax>CacheDisable <var>cache_type</var> <var>url-string</var></syntax>
+<description>Disable caching of specified URLs</description>
+<syntax>CacheDisable <var> url-string</var></syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<var>url-string</var>.</p>
<example><title>Example</title>
- CacheDisable disk /local_files
+ CacheDisable /local_files
</example>
</usage>
</contextlist>
<usage>
- <p>The maximum time in seconds to cache a document. The
- <directive>CacheMaxExpire</directive> takes precedence over the
- <code>Expires</code> field from the header.</p>
+ <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
<directivesynopsis>
<name>CacheDefaultExpire</name>
-<description>The default time in seconds to cache a document</description>
+<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 default time in seconds to cache a document if the page does not have
- an expiry date in the <code>Expires</code> field.</p>
+ <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
<directivesynopsis>
<name>CacheIgnoreNoLastMod</name>
-<description>Ignore responses where there is no Last Modified
-Header</description>
+<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>Ignore responses where there is no Last Modified Header.</p>
+ <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
<directivesynopsis>
<name>CacheIgnoreCacheControl</name>
-<description>Ignore requests from the client for uncached
-content</description>
+<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>Ignore requests from the client for uncached content</p>
+ <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
<directivesynopsis>
<name>CacheLastModifiedFactor</name>
-<description>The factor used to estimate the Expires date from the
-LastModified date</description>
+<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>The factor used to estimate the Expires date from the LastModified date.</p>
+ <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
<directivesynopsis>
<name>CacheForceCompletion</name>
-<description>Percentage of download to arrive for the cache to force
-complete transfer</description>
+<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>Percentage of download to arrive for the cache to force complete transfer.</p>
+ <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">
+ <note type="warning"><title>Note:</title>
This feature is currently <em>not</em> implemented.
</note>
</usage>
</contextlist>
<usage>
- <p>Maximum number of bytes of a streamed response (<em>i.e.</em>, a
- response where the entire content is not available all at once, such
- as a proxy or CGI response) to buffer before deciding if the response
- is cacheable. By default, a streamed response will <em>not</em> be
- cached unless it has a <code>Content-Length</code> header. The reason
- for this is to avoid using a large amount of memory to buffer a partial
- response that might end up being too large to fit in the cache anyway.
- To enable caching of streamed responses, use <directive
- >CacheMaxStreamingBuffer</directive> to specify the maximum amount of
- buffer space to use per request.</p>
+ <p>The <directive>CacheMaxStreamingBuffer</directive> directive
+ specifies the maximum number of bytes of a streamed response to
+ buffer before deciding that the response is too big to cache.
+ A streamed response is one in which the entire content is not
+ immediately available and in which the <code>Content-Length</code>
+ may not be known. Sources of streaming responses include proxied
+ responses and the output of CGI scripts. By default, a streamed
+ response will <em>not</em> be cached unless it has a
+ <code>Content-Length</code> header. The reason for this is to
+ avoid using a large amount of memory to buffer a partial response
+ that might end up being too large to fit in the cache.
+ The <directive>CacheMaxStreamingBuffer</directive> directive allows
+ buffering of streamed responses that don't contain a
+ <code>Content-Length</code> up to the specified maximum amount of
+ space. If the maximum buffer space is reached, the buffered
+ content is discarded and the attempt to cache is abandoned.</p>
<note><title>Note:</title>
<p>Using a nonzero value for <directive
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