repo_zf1/documentation/manual/en/module_specs/Zend_Cache-Backends.xml

<?xml version="1.0" encoding="UTF-8"?>
<!-- Reviewed: no -->
<sect1 id="zend.cache.backends">
    <title>Zend_Cache Backends</title>
    <para>
        There are two kinds of backends: standard ones and extended ones. Of course, extended
        backends offer more features.
    </para>
    <sect2 id="zend.cache.backends.file">
        <title>Zend_Cache_Backend_File</title>
        <para>
            This (extended) backends stores cache records into files (in a choosen directory).
        </para>
        <para>
            Available options are :
        </para>
        <table id="zend.cache.backends.file.table">
            <title>File Backend Options</title>
            <tgroup cols="4">
                 <thead>
                      <row>
                        <entry>Option</entry>
                        <entry>Data Type</entry>
                        <entry>Default Value</entry>
                        <entry>Description</entry>
                    </row>
                 </thead>
                 <tbody>
                      <row>
                          <entry><emphasis>cache_dir</emphasis></entry>
                          <entry><type>String</type></entry>
                          <entry>'<filename>/tmp/</filename>'</entry>
                          <entry>
                              Directory where to store cache files
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>file_locking</emphasis></entry>
                          <entry><type>Boolean</type></entry>
                          <entry><constant>TRUE</constant></entry>
                          <entry>
                            Enable or disable file_locking : Can avoid cache corruption under
                            bad circumstances but it doesn't help on multithread webservers
                            or on <acronym>NFS</acronym> filesystems...
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>read_control</emphasis></entry>
                          <entry><type>Boolean</type></entry>
                          <entry><constant>TRUE</constant></entry>
                          <entry>
                            Enable / disable read control : if enabled, a control key is
                            embedded in the cache file and this key is compared with the
                            one calculated after the reading.
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>read_control_type</emphasis></entry>
                          <entry><type>String</type></entry>
                          <entry>'crc32'</entry>
                          <entry>
                            Type of read control (only if read control is enabled). Available values
                            are : 'md5' (best but slowest), 'crc32' (lightly less safe but faster,
                            better choice), 'adler32' (new choice, faster than crc32),
                            'strlen' for a length only test (fastest).
                        </entry>
                      </row>
                      <row>
                          <entry><emphasis>hashed_directory_level</emphasis></entry>
                          <entry><type>Integer</type></entry>
                          <entry>0</entry>
                          <entry>
                            Hashed directory structure level : 0 means "no hashed directory
                             structure", 1 means "one level of directory", 2 means "two levels"...
                             This option can speed up the cache only when you have many thousands of
                             cache files. Only specific benchs can help you to choose the perfect
                             value for you. Maybe, 1 or 2 is a good start.
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>hashed_directory_umask</emphasis></entry>
                          <entry><type>Integer</type></entry>
                          <entry>0700</entry>
                          <entry>
                              Umask for the hashed directory structure
                        </entry>
                      </row>
                      <row>
                          <entry><emphasis>file_name_prefix</emphasis></entry>
                          <entry><type>String</type></entry>
                          <entry>'zend_cache'</entry>
                          <entry>
                              prefix for cache files ; be really careful with this option because
                              a too generic value in a system cache dir
                              (like <filename>/tmp</filename>) can cause disasters when cleaning
                              the cache
                        </entry>
                      </row>
                      <row>
                          <entry><emphasis>cache_file_umask</emphasis></entry>
                          <entry><type>Integer</type></entry>
                          <entry>0700</entry>
                          <entry>
                              umask for cache files
                          </entry>
                      </row>
                       <row>
                          <entry><emphasis>metatadatas_array_max_size</emphasis></entry>
                          <entry><type>Integer</type></entry>
                          <entry>100</entry>
                          <entry>
                              internal max size for the metadatas array (don't change this value
                              unless you know what you are doing)
                          </entry>
                      </row>
                  </tbody>
              </tgroup>
          </table>
    </sect2>
    <sect2 id="zend.cache.backends.sqlite">
        <title>Zend_Cache_Backend_Sqlite</title>
        <para>
            This (extended) backends stores cache records into a SQLite database.
        </para>
        <para>
            Available options are :
        </para>
        <table id="zend.cache.backends.sqlite.table">
            <title>Sqlite Backend Options</title>
            <tgroup cols="4">
                 <thead>
                      <row>
                           <entry>Option</entry>
                        <entry>Data Type</entry>
                        <entry>Default Value</entry>
                        <entry>Description</entry>
                    </row>
                 </thead>
                 <tbody>
                      <row>
                          <entry><emphasis>cache_db_complete_path (mandatory)</emphasis></entry>
                          <entry><type>String</type></entry>
                          <entry><constant>NULL</constant></entry>
                          <entry>
                              The complete path (filename included) of the SQLite database
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>automatic_vacuum_factor</emphasis></entry>
                          <entry><type>Integer</type></entry>
                          <entry>10</entry>
                          <entry>
                              Disable / Tune the automatic vacuum process. The automatic vacuum
                              process defragment the database file (and make it smaller) when a
                              <methodname>clean()</methodname> or <methodname>delete()</methodname>
                              is called: 0 means no automatic vacuum ; 1 means systematic vacuum
                              (when <methodname>delete()</methodname> or
                              <methodname>clean()</methodname> methods are called) ; x (integer) >
                              1 => automatic vacuum randomly 1 times on x
                              <methodname>clean()</methodname> or
                              <methodname>delete()</methodname>.
                          </entry>
                      </row>
                  </tbody>
              </tgroup>
          </table>
    </sect2>
    <sect2 id="zend.cache.backends.memcached">
        <title>Zend_Cache_Backend_Memcached</title>
        <para>
            This (extended) backends stores cache records into a memcached server. <ulink
                url="http://www.danga.com/memcached/">memcached</ulink> is a high-performance,
            distributed memory object caching system. To use this backend, you need a memcached
            daemon and <ulink url="http://pecl.php.net/package/memcache">the memcache
                <acronym>PECL</acronym> extension</ulink>.
        </para>
        <para>
            Be careful : with this backend, "tags" are not supported for the moment as
            the "doNotTestCacheValidity=true" argument.
        </para>
        <para>
            Available options are :
        </para>
        <table id="zend.cache.backends.memcached.table">
            <title>Memcached Backend Options</title>
            <tgroup cols="4">
                 <thead>
                      <row>
                        <entry>Option</entry>
                        <entry>Data Type</entry>
                        <entry>Default Value</entry>
                        <entry>Description</entry>
                    </row>
                 </thead>
                 <tbody>
                      <row>
                          <entry><emphasis>servers</emphasis></entry>
                          <entry><type>Array</type></entry>
                          <entry>
                              <command>array(array('host' => 'localhost', 'port' => 11211,
                                  'persistent' => true, 'weight' => 1, 'timeout' => 5,
                                  'retry_interval' => 15, 'status' => true,
                                  'failure_callback' => '' ))</command>
                          </entry>
                          <entry>
                              An array of memcached servers ; each memcached server is described by
                              an associative array : 'host' => (string) : the name of the memcached
                              server, 'port' => (int) : the port of the memcached server,
                              'persistent' => (bool) : use or not persistent connections to this
                              memcached server 'weight' => (int) :the weight of the memcached
                              server, 'timeout' => (int) :the time out of the memcached server,
                              'retry_interval' => (int) :the retry interval of the memcached server,
                              'status' => (bool) :the status of the memcached server,
                              'failure_callback' => (callback) : the failure_callback of the
                              memcached server
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>compression</emphasis></entry>
                          <entry><type>Boolean</type></entry>
                          <entry><constant>FALSE</constant></entry>
                          <entry>
                             <constant>TRUE</constant> if you want to use on-the-fly compression
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>compatibility</emphasis></entry>
                          <entry><type>Boolean</type></entry>
                          <entry><constant>FALSE</constant></entry>
                          <entry>
                             <constant>TRUE</constant> if you want to use this compatibility mode
                             with old memcache servers or extensions
                          </entry>
                      </row>
                  </tbody>
              </tgroup>
          </table>
    </sect2>
    <sect2 id="zend.cache.backends.apc">
        <title>Zend_Cache_Backend_Apc</title>
        <para>
            This (extended) backends stores cache records in shared memory through
            the <ulink url="http://pecl.php.net/package/APC">APC</ulink> (Alternative
            <acronym>PHP</acronym> Cache) extension (which is of course need for using this
            backend).
        </para>
        <para>
            Be careful : with this backend, "tags" are not supported for the moment as
            the "doNotTestCacheValidity=true" argument.
        </para>
        <para>
            There is no option for this backend.
        </para>
    </sect2>
    <sect2 id="zend.cache.backends.xcache">
        <title>Zend_Cache_Backend_Xcache</title>
        <para>
            This backends stores cache records in shared memory through
            the <ulink url="http://xcache.lighttpd.net/">XCache</ulink> extension
            (which is of course need for using this backend).
        </para>
        <para>
            Be careful : with this backend, "tags" are not supported for the moment as
            the "doNotTestCacheValidity=true" argument.
        </para>
        <para>
            Available options are :
        </para>
        <table id="zend.cache.backends.xcache.table">
            <title>Xcache Backend Options</title>
            <tgroup cols="4">
                 <thead>
                      <row>
                        <entry>Option</entry>
                        <entry>Data Type</entry>
                        <entry>Default Value</entry>
                        <entry>Description</entry>
                    </row>
                 </thead>
                 <tbody>
                      <row>
                          <entry><emphasis>user</emphasis></entry>
                          <entry><type>String</type></entry>
                          <entry><constant>NULL</constant></entry>
                          <entry>
                              <filename>xcache.admin.user</filename>, necessary for the
                              <methodname>clean()</methodname> method
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>password</emphasis></entry>
                          <entry><type>String</type></entry>
                          <entry><constant>NULL</constant></entry>
                          <entry>
                              <filename>xcache.admin.pass</filename> (in clear form, not
                              <acronym>MD5</acronym>), necessary for the
                              <methodname>clean()</methodname> method
                          </entry>
                      </row>
                  </tbody>
              </tgroup>
          </table>
    </sect2>
    <sect2 id="zend.cache.backends.platform">
        <title>Zend_Cache_Backend_ZendPlatform</title>
        <para>
            This backend uses content caching <acronym>API</acronym> of the <ulink
                url="http://www.zend.com/en/products/platform/">Zend Platform</ulink> product.
            Naturally, to use this backend you need to have Zend Platform installed.
        </para>
        <para>
            This backend supports tags, but does not support
            <constant>CLEANING_MODE_NOT_MATCHING_TAG</constant> cleaning mode.
        </para>
        <para>
            Specify this backend using a word separator -- '-', '.', ' ', or '_'
            -- between the words 'Zend' and 'Platform' when using the
            <methodname>Zend_Cache::factory()</methodname> method:
        </para>
        <programlisting language="php"><![CDATA[
$cache = Zend_Cache::factory('Core', 'Zend Platform');
]]></programlisting>
        <para>
            There are no options for this backend.
        </para>
    </sect2>
    <sect2 id="zend.cache.backends.twolevels">
        <title>Zend_Cache_Backend_TwoLevels</title>
        <para>
            This (extend) backend is an hybrid one. It stores cache records in two other backends :
            a fast one (but limited) like Apc, Memcache... and a "slow" one like File, Sqlite...
        </para>
        <para>
            This backend will use the priority parameter (given at the frontend level when storing a
            record) and the remaining space in the fast backend to optimize the usage of these two
            backends.
        </para>
        <para>
            Specify this backend using a word separator -- '-', '.', ' ', or '_'
            -- between the words 'Two' and 'Levels' when using the
            <methodname>Zend_Cache::factory()</methodname> method:
        </para>
        <programlisting language="php"><![CDATA[
$cache = Zend_Cache::factory('Core', 'Two Levels');
]]></programlisting>
        <para>
            Available options are :
        </para>
        <table id="zend.cache.backends.twolevels.table">
            <title>TwoLevels Backend Options</title>
            <tgroup cols="4">
                 <thead>
                      <row>
                        <entry>Option</entry>
                        <entry>Data Type</entry>
                        <entry>Default Value</entry>
                        <entry>Description</entry>
                    </row>
                 </thead>
                 <tbody>
                      <row>
                          <entry><emphasis>slow_backend</emphasis></entry>
                          <entry><type>String</type></entry>
                          <entry>File</entry>
                          <entry>
                              the "slow" backend name
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>fast_backend</emphasis></entry>
                          <entry><type>String</type></entry>
                          <entry>Apc</entry>
                          <entry>
                              the "fast" backend name
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>slow_backend_options</emphasis></entry>
                          <entry><type>Array</type></entry>
                          <entry><methodname>array()</methodname></entry>
                          <entry>
                              the "slow" backend options
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>fast_backend_options</emphasis></entry>
                          <entry><type>Array</type></entry>
                          <entry><methodname>array()</methodname></entry>
                          <entry>
                              the "fast" backend options
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>slow_backend_custom_naming</emphasis></entry>
                          <entry><type>Boolean</type></entry>
                          <entry><constant>FALSE</constant></entry>
                          <entry>
                              if <constant>TRUE</constant>, the slow_backend argument is used as a
                              complete class name; if <constant>FALSE</constant>,
                              the frontend argument is used as the end of
                              "<classname>Zend_Cache_Backend_</classname>[...]" class name
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>fast_backend_custom_naming</emphasis></entry>
                          <entry><type>Boolean</type></entry>
                          <entry><constant>FALSE</constant></entry>
                          <entry>
                              if <constant>TRUE</constant>, the fast_backend argument is used as a
                              complete class name; if <constant>FALSE</constant>,
                              the frontend argument is used as the end of
                              "<classname>Zend_Cache_Backend_</classname>[...]" class name
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>slow_backend_autoload</emphasis></entry>
                          <entry><type>Boolean</type></entry>
                          <entry><constant>FALSE</constant></entry>
                          <entry>
                              if <constant>TRUE</constant>, there will no require_once for the
                              slow backend (useful only for custom backends)
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>fast_backend_autoload</emphasis></entry>
                          <entry><type>Boolean</type></entry>
                          <entry><constant>FALSE</constant></entry>
                          <entry>
                              if <constant>TRUE</constant>, there will no require_once for the fast
                              backend (useful only for custom backends)
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>auto_refresh_fast_cache</emphasis></entry>
                          <entry><type>Boolean</type></entry>
                          <entry><constant>TRUE</constant></entry>
                          <entry>
                              if <constant>TRUE</constant>, auto refresh the fast cache when a
                              cache record is hit
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>stats_update_factor</emphasis></entry>
                          <entry><type>Integer</type></entry>
                          <entry>10</entry>
                          <entry>
                              disable / tune the computation of the fast backend filling percentage
                              (when saving a record into cache, computation of the fast backend
                              filling percentage randomly 1 times on x cache writes)
                          </entry>
                      </row>
                  </tbody>
              </tgroup>
          </table>
    </sect2>
    <sect2 id="zend.cache.backends.zendserver">
        <title>Zend_Cache_Backend_ZendServer_Disk and Zend_Cache_Backend_ZendServer_ShMem</title>
        <para>
            These backends store cache records using <ulink
                url="http://www.zend.com/en/products/server/downloads-all?zfs=zf_download">Zend
                Server</ulink> caching functionality.
        </para>
        <para>
             Be careful: with these backends, "tags" are not supported for the moment as the
             "doNotTestCacheValidity=true" argument.
        </para>
        <para>
             These backend work only withing Zend Server environment for pages requested through
             <acronym>HTTP</acronym> or <acronym>HTTPS</acronym> and don't work for command line
             script execution
        </para>
        <para>
            Specify this backend using parameter <emphasis>customBackendNaming</emphasis> as
            <constant>TRUE</constant> when using the <methodname>Zend_Cache::factory()</methodname>
            method:
        </para>
        <programlisting language="php"><![CDATA[
$cache = Zend_Cache::factory('Core', 'Zend_Cache_Backend_ZendServer_Disk',
                             $frontendOptions, $backendOptions, false, true);
]]></programlisting>
        <para>
            There is no option for this backend.
        </para>
    </sect2>

    <sect2 id="zend.cache.backends.static">
        <title>Zend_Cache_Backend_Static</title>
        <para>
            This backend works in concert with <classname>Zend_Cache_Frontend_Capture</classname>
            (the two must be used together) to save the output from requests as static files. This
            means the static files are served directly on subsequent requests without any
            involvement of <acronym>PHP</acronym> or Zend Framework at all.
        </para>
        <para>
            The benefits of this cache include a large throughput increase since
            all subsequent requests return the static file and don't need any
            dynamic processing. Of course this also has some disadvantages. The
            only way to retry the dynamic request is to purge the cached file
            from elsewhere in the application (or via a cronjob if timed). It
            is also restricted to single-server applications where only one
            filesystem is used. Nevertheless, it can be a powerful means of
            getting more performance without incurring the cost of a proxy on
            single machines.
        </para>
        <para>
            Before describing its options, you should note this needs some
            changes to the default <filename>.htaccess</filename> file in order for requests to be
            directed to the static files if they exist. Here's an example of
            a simple application caching some content, including two specific
            feeds which need additional treatment to serve a correct
            Content-Type header:
        </para>
        <programlisting language="text"><![CDATA[
AddType application/rss+xml .xml
AddType application/atom+xml .xml

RewriteEngine On

RewriteCond %{REQUEST_URI} feed/rss$
RewriteCond %{DOCUMENT_ROOT}/cached/%{REQUEST_URI}.xml -f
RewriteRule .* cached/%{REQUEST_URI}.xml [L,T=application/rss+xml]

RewriteCond %{REQUEST_URI} feed/atom$
RewriteCond %{DOCUMENT_ROOT}/cached/%{REQUEST_URI}.xml -f
RewriteRule .* cached/%{REQUEST_URI}.xml [L,T=application/atom+xml]

RewriteCond %{DOCUMENT_ROOT}/cached/index.html -f
RewriteRule ^/*$ cached/index.html [L]
RewriteCond %{DOCUMENT_ROOT}/cached/%{REQUEST_URI}.(html|xml|json|opml|svg) -f
RewriteRule .* cached/%{REQUEST_URI}.%1 [L]

RewriteCond %{REQUEST_FILENAME} -s [OR]
RewriteCond %{REQUEST_FILENAME} -l [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^.*$ - [NC,L]

RewriteRule ^.*$ index.php [NC,L]
]]></programlisting>
        <para>
            The above assumes static files are cached to the directory
            <filename>./public/cached</filename>. We'll cover the option setting this location,
            "public_dir", below.
        </para>
        <para>
            Due to the nature of static file caching, the backend class offers two additional
            methods: <methodname>remove()</methodname> and
            <methodname>removeRecursively()</methodname>. Both accept a request
            <acronym>URI</acronym>, which when mapped to the "public_dir" where static files are
            cached, and has a pre-stored extension appended, provides the name of either a static
            file to delete, or a directory path to delete recursively. Due to the
            restraints of <classname>Zend_Cache_Backend_Interface</classname>, all
            other methods such as <methodname>save()</methodname> accept an ID which
            is calculated by applying <methodname>bin2hex()</methodname> to a request
            <acronym>URI</acronym>.
        </para>
        <para>
            Given the level at which static caching operates, static file caching is addressed for
            simpler use with the <classname>Zend_Controller_Action_Helper_Cache</classname> action
            helper. This helper assists in setting which actions of a controller to cache, with what
            tags, and with which extension. It also offers methods for purging the cache by request
            <acronym>URI</acronym> or tag. Static file caching is also assisted by
            <classname>Zend_Cache_Manager</classname> which includes pre-configured configuration
            templates for a static cache (as <constant>Zend_Cache_Manager::PAGECACHE</constant> or
            "page"). The defaults therein can be configured as needed to set up a "public_dir"
            location for caching, etc.
        </para>
        <note>
            <para>
                It should be noted that the static cache actually uses a secondary cache to store
                tags (obviously we can't store them elsewhere since a static cache does not invoke
                <acronym>PHP</acronym> if working correctly). This is just a standard Core cache, and
                should use a persistent backend such as File or TwoLevels (to take advantage of
                memory storage without sacrificing permanent persistance). The backend includes the
                option "tag_cache" to set this up (it is obligatory), or the
                <methodname>setInnerCache()</methodname> method.
            </para>
        </note>
        <table id="zend.cache.backends.static.table">
            <title>Static Backend Options</title>
            <tgroup cols="4">
                 <thead>
                      <row>
                        <entry>Option</entry>
                        <entry>Data Type</entry>
                        <entry>Default Value</entry>
                        <entry>Description</entry>
                    </row>
                 </thead>
                 <tbody>
                      <row>
                          <entry><emphasis>public_dir</emphasis></entry>
                          <entry><type>String</type></entry>
                          <entry><constant>NULL</constant></entry>
                          <entry>
                              Directory where to store static files. This must exist
                              in your public directory.
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>file_locking</emphasis></entry>
                          <entry><type>Boolean</type></entry>
                          <entry><constant>TRUE</constant></entry>
                          <entry>
                            Enable or disable file_locking : Can avoid cache corruption under
                            bad circumstances but it doesn't help on multithread webservers
                            or on <acronym>NFS</acronym> filesystems...
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>read_control</emphasis></entry>
                          <entry><type>Boolean</type></entry>
                          <entry><constant>TRUE</constant></entry>
                          <entry>
                            Enable / disable read control : if enabled, a control key is
                            embedded in the cache file and this key is compared with the
                            one calculated after the reading.
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>read_control_type</emphasis></entry>
                          <entry><type>String</type></entry>
                          <entry>'crc32'</entry>
                          <entry>
                            Type of read control (only if read control is enabled). Available values
                            are : 'md5' (best but slowest), 'crc32' (lightly less safe but faster,
                            better choice), 'adler32' (new choice, faster than crc32),
                            'strlen' for a length only test (fastest).
                        </entry>
                      </row>
                      <row>
                          <entry><emphasis>cache_file_umask</emphasis></entry>
                          <entry><type>Integer</type></entry>
                          <entry>0700</entry>
                          <entry>
                              umask for cached files.
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>cache_directory_umask</emphasis></entry>
                          <entry><type>Integer</type></entry>
                          <entry>0700</entry>
                          <entry>
                              Umask for directories created within public_dir.
                        </entry>
                      </row>

                      <row>
                          <entry><emphasis>file_extension</emphasis></entry>
                          <entry><type>String</type></entry>
                          <entry>'<filename>.html</filename>'</entry>
                          <entry>
                              Default file extension for static files created. This can be
                              configured on the fly, see
                              <methodname>Zend_Cache_Backend_Static::save()</methodname> though
                              generally it's recommended to rely on
                              <classname>Zend_Controller_Action_Helper_Cache</classname> when
                              doing so since it's simpler that way than messing with
                              arrays or serialization manually.
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>index_filename</emphasis></entry>
                          <entry><type>String</type></entry>
                          <entry>'index'</entry>
                          <entry>
                              If a request <acronym>URI</acronym> does not contain sufficient
                              information to construct a static file (usually this means an index
                              call, e.g. <acronym>URI</acronym> of '/'), the index_filename is used
                              instead. So '' or '/' would map to '<filename>index.html</filename>'
                              (assuming the default file_extension is '<filename>.html</filename>').
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>tag_cache</emphasis></entry>
                          <entry><type>Object</type></entry>
                          <entry><constant>NULL</constant></entry>
                          <entry>
                              Used to set an 'inner' cache utilised to store tags
                              and file extensions associated with static files. This
                              <emphasis>must</emphasis> be set or the static cache cannot be tracked
                              and managed.
                          </entry>
                      </row>
                      <row>
                          <entry><emphasis>disable_caching</emphasis></entry>
                          <entry><type>Boolean</type></entry>
                          <entry><constant>FALSE</constant></entry>
                          <entry>
                              If set to <constant>TRUE</constant>, static files will not be cached.
                              This will force all requests to be dynamic even if marked
                              to be cached in Controllers. Useful for debugging.
                          </entry>
                      </row>
                  </tbody>
              </tgroup>
          </table>
    </sect2>

</sect1>
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