Cache¶

Allgemeines über Caching¶

Caching ist als Methode zur temporären Speicherung gedacht, um die Serverlast zu reduzieren. Zum Beispiel können die Ergebnisse eine zeitintensiven Datenbankabfrage gespeichert werden, damit die Abfrage nicht bei jedem Aufruf der Seite ausgeführt werden muss.

Wenn man dies im Hinterkopf hat wird klar, dass Caching kein permanenter Speicher ist und nicht dazu benutzt wird, um irgendetwas permanent zu speichern. Sondern nur zum Cachen von Daten dient, die wieder abgerufen werden können, wenn sie benötigt werden.

Cache Engines in Cake¶

New in 1.2 are several cache engines or cache backends. These interface transparently with the cache helper, allowing you to store view caches in a multitude of media without worrying about the specifics of that media. The choice of cache engine is controlled through the app/config/core.php config file. Most options for each caching engine are listed in the core.php config file and more detailed information on each caching engine can be found in the Caching Section.

File

The File Engine is the default caching engine used by cake. It writes flat files to the filesystem and it has several optional parameters but works well with the defaults.

APC

The APC engine implements the Alternative PHP Cache opcode Cacher. Like XCache, this engine caches the compiled PHP opcode.

XCache

The XCache caching engine is functionally similar to APC other than it implements the XCache opcode caching engine. It requires the entry of a user and password to work properly.

Memcache

The Memcache engine works with a memcaching server allowing you to create a cache object in system memory. More information on memcaching can be found on php.net and memcached

Cache Helper Configuration¶

View Caching and the Cache Helper have several important configuration elements. They are detailed below.

To use the cache helper in any view or controller, you must first uncomment and set Configure::Cache.check to true in core.php of your app/config folder. If this is not set to true, then the cache will not be checked or created.

Configure::write('Cache.check', true);

Caching in the Controller¶

Any controllers that utilize caching functionality need to include the CacheHelper in their $helpers array.

var $helpers = array('Cache');

You also need to indicate which actions need caching, and how long each action will be cached. This is done through the $cacheAction variable in your controllers. $cacheAction should be set to an array which contains the actions you want cached, and the duration in seconds you want those views cached. The time value can be expressed in a strtotime() format. (ie. „1 hour“, or „3 minutes“).

Using the example of an ArticlesController, that receives a lot of traffic that needs to be cached.

Cache frequently visited Articles for varying lengths of time

var $cacheAction = array(
    'view/23' => 21600,
    'view/48' => 36000,
    'view/52'  => 48000
);

Remember to use your routes in the $cacheAction if you have any.

Cache an entire action in this case a large listing of articles

var $cacheAction = array(
    'archives/' => '60000'
);

Cache every action in the controller using a strtotime() friendly time to indicate Controller wide caching time.

var $cacheAction = "1 hour";

You can also enable controller/component callbacks for cached views created with CacheHelper. To do so you must use the array format for $cacheAction and create an array like the following:

var $cacheAction = array(
    'view' => array('callbacks' => true, 'duration' => 21600),
    'add' => array('callbacks' => true, 'duration' => 36000),
    'index'  => array('callbacks' => true, 'duration' => 48000)
);

By setting callbacks => true you tell CacheHelper that you want the generated files to create the components and models for the controller. As well as, fire the component initialize, controller beforeFilter, and component startup callbacks.

callbacks => true partly defeats the purpose of caching. This is also the reason it is disabled by default.

Marking Non-Cached Content in Views¶

There will be times when you don’t want an entire view cached. For example, certain parts of the page may look different whether a user is currently logged in or browsing your site as a guest.

To indicate blocks of content that are not to be cached, wrap them in <cake:nocache> </cake:nocache> like so:

<cake:nocache>
<?php if ($session->check('User.name')) : ?>
    Welcome, <?php echo $session->read('User.name')?>.
<?php else: ?>
    <?php echo $html->link('Login', 'users/login')?>
<?php endif; ?>
</cake:nocache>

It should be noted that once an action is cached, the controller method for the action will not be called - otherwise what would be the point of caching the page. Therefore, it is not possible to wrap <cake:nocache> </cake:nocache> around variables which are set from the controller as they will be null.

Clearing the Cache¶

It is important to remember that the Cake will clear a cached view if a model used in the cached view is modified. For example, if a cached view uses data from the Post model, and there has been an INSERT, UPDATE, or DELETE query made to a Post, the cache for that view is cleared, and new content is generated on the next request.

If you need to manually clear the cache, you can do so by calling Cache::clear(). This will clear all cached data, excluding cached view files. If you need to clear the cached view files, use clearCache().