path: root/docs/manual/mod/mod_cache.xml

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

<name>mod_cache</name>
<description>Content cache keyed to URIs.</description>
<status>Extension</status>
<sourcefile>mod_cache.c</sourcefile>
<identifier>cache_module</identifier>

<summary>
    <note type="warning">This module should be used with care and
    can be used to circumvent <directive 
    module="mod_authz_host">Allow</directive> and <directive 
    module="mod_authz_host">Deny</directive> directives. You 
    should not enable caching for any content to which you wish
    to limit access by client host name, address or environment
    variable.</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">CacheDirLevels</directive>
        <directive module="mod_disk_cache">CacheDirLength</directive>
        <directive module="mod_disk_cache">CacheMinFileSize</directive>
        <directive module="mod_disk_cache">CacheMaxFileSize</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 />
        # If you want to use mod_disk_cache instead of mod_mem_cache,<br />
        # uncomment the line above and comment out the LoadModule line below.<br />
        &lt;IfModule mod_disk_cache.c&gt;<br />
        <indent>
          CacheRoot c:/cacheroot<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 />
        <br />
        # When acting as a proxy, don't cache the list of security updates<br />
        CacheDisable http://security.update.server/update-list/<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>

    <p>When acting as a forward proxy server, <var>url-string</var> can
    also be used to specify remote sites and proxy protocols which 
    caching should be enabled for.</p>
 
    <example>
      # Cache proxied url's<br />
      CacheEnable  disk  /<br /><br />
      # Cache FTP-proxied url's<br />
      CacheEnable  disk  ftp://<br /><br />
      # Cache content from www.apache.org<br />
      CacheEnable  disk  http://www.apache.org/<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>CacheMinExpire</name>
<description>The minimum time in seconds to cache a document</description>
<syntax>CacheMinExpire <var>seconds</var></syntax>
<default>CacheMinExpire 0</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>

<usage>
    <p>The <directive>CacheMinExpire</directive> directive specifies the minimum number of
    seconds for which cachable 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>


    <example>
      CacheMinExpire 3600
    </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 request to not serve cached content to client</description>
<syntax>CacheIgnoreCacheControl On|Off</syntax>
<default>CacheIgnoreCacheControl Off</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>

<usage>
    <p>Ordinarily, requests containing a Cache-Control: no-cache or
    Pragma: no-cache header value will not be served from the cache.  The
    <directive>CacheIgnoreCacheControl</directive> directive allows this
    behavior to be overridden.  <directive>CacheIgnoreCacheControl</directive>
    On 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>

    <example>
      CacheIgnoreCacheControl On
    </example>

    <note type="warning"><title>Warning:</title>
       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.
    </note>
</usage>
<seealso><directive module="mod_cache">CacheStorePrivate</directive></seealso>
<seealso><directive module="mod_cache">CacheStoreNoStore</directive></seealso>
</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>CacheIgnoreHeaders</name>
<description>Do not store the given HTTP header(s) in the cache.
</description>
<syntax>CacheIgnoreHeaders <var>header-string</var> [<var>header-string</var>] ...</syntax>
<default>CacheIgnoreHeaders None</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>

<usage>
    <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 <directive>CacheIgnoreHeaders</directive>:</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><directive>CacheIgnoreHeaders</directive> 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><directive>CacheIgnoreHeaders</directive> 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), <directive>CacheIgnoreHeaders</directive> can be set to
    <code>None</code>.</p>

    <example><title>Example 1</title>
      CacheIgnoreHeaders Set-Cookie
    </example>

    <example><title>Example 2</title>
      CacheIgnoreHeaders None
    </example>

    <note type="warning"><title>Warning:</title>
      If headers like <code>Expires</code> which are needed for proper cache
      management are not stored due to a
      <directive>CacheIgnoreHeaders</directive> setting, the behaviour of
      mod_cache is undefined.
    </note>
</usage>
</directivesynopsis>

<directivesynopsis>
<name>CacheStorePrivate</name>
<description>Attempt to cache responses that the server has marked as private</description>
<syntax>CacheStorePrivate On|Off</syntax>
<default>CacheStorePrivate Off</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>

<usage>
    <p>Ordinarily, responses with Cache-Control: private header values will not
       be stored in the cache.  The <directive>CacheStorePrivate</directive>
       directive allows this behavior to be overridden.
       <directive>CacheStorePrivate</directive> 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>

    <example>
      CacheStorePrivate On
    </example>

    <note type="warning"><title>Warning:</title>
       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.
    </note>
</usage>
<seealso><directive module="mod_cache">CacheIgnoreCacheControl</directive></seealso>
<seealso><directive module="mod_cache">CacheStoreNoStore</directive></seealso>
</directivesynopsis>

<directivesynopsis>
<name>CacheStoreNoStore</name>
<description>Attempt to cache requests or responses that have been marked as no-store.</description>
<syntax>CacheStoreNoStore On|Off</syntax>
<default>CacheStoreNoStore Off</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>

<usage>
    <p>Ordinarily, requests or responses with Cache-Control: no-store header
       values will not be stored in the cache.  The
       <directive>CacheStoreNoCache</directive> directive allows this
       behavior to be overridden.  <directive>CacheStoreNoCache</directive> 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>

    <example>
      CacheStoreNoStore On
    </example>

    <note type="warning"><title>Warning:</title>
       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.
    </note>
</usage>
<seealso><directive module="mod_cache">CacheIgnoreCacheControl</directive></seealso>
<seealso><directive module="mod_cache">CacheStorePrivate</directive></seealso>
</directivesynopsis>
</modulesynopsis>