docs/manual/mod/mod_cache.xml

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<!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
<modulesynopsis>

<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>