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Caching

Caching is frequently used to reduce the time it takes to create or read from other resources. Caching is often used to make reading from expensive resources less expensive. You can easily store the results of expensive queries, or remote webservice access that doesn’t frequently change in a cache. Once in the cache, re-reading the stored resource from the cache is much cheaper than accessing the remote resource.

Caching in CakePHP is primarily facilitated by the Cache class. This class provides a set of static methods that provide a uniform API to dealing with all different types of Caching implementations. CakePHP comes with several cache engines built-in, and provides an easy system to implement your own caching systems. The built-in caching engines are:

  • FileCache File cache is a simple cache that uses local files. It is the slowest cache engine, and doesn’t provide as many features for atomic operations. However, since disk storage is often quite cheap, storing large objects, or elements that are infrequently written work well in files. This is the default Cache engine for 2.3+
  • ApcCache APC cache uses the PHP APC extension. This extension uses shared memory on the webserver to store objects. This makes it very fast, and able to provide atomic read/write features. By default CakePHP in 2.0-2.2 will use this cache engine if it’s available.
  • Wincache Wincache uses the Wincache extension. Wincache is similar to APC in features and performance, but optimized for Windows and IIS.
  • XcacheEngine Xcache is a PHP extension that provides similar features to APC.
  • MemcacheEngine Uses the Memcache extension. Memcache provides a very fast cache system that can be distributed across many servers, and provides atomic operations.
  • MemcachedEngine Uses the Memcached extension. It also interfaces with memcache but provides better performance.
  • RedisEngine Uses the phpredis extension. Redis provides a fast and persistent cache system similar to memcached, also provides atomic operations.

Changed in version 2.3: FileEngine is always the default cache engine. In the past a number of people had difficulty setting up and deploying APC correctly both in cli + web. Using files should make setting up CakePHP simpler for new developers.

Changed in version 2.5: The Memcached engine was added. And the Memcache engine was deprecated.

Regardless of the CacheEngine you choose to use, your application interacts with Cache in a consistent manner. This means you can easily swap cache engines as your application grows. In addition to the Cache class, the CacheHelper allows for full page caching, which can greatly improve performance as well.

Configuring Cache class

Configuring the Cache class can be done anywhere, but generally you will want to configure Cache in app/Config/bootstrap.php. You can configure as many cache configurations as you need, and use any mixture of cache engines. CakePHP uses two cache configurations internally, which are configured in app/Config/core.php. If you are using APC or Memcache you should make sure to set unique keys for the core caches. This will prevent multiple applications from overwriting each other’s cached data.

Using multiple cache configurations can help reduce the number of times you need to use Cache::set() as well as centralize all your cache settings. Using multiple configurations also lets you incrementally change the storage as needed.

Note

You must specify which engine to use. It does not default to File.

Example:

Cache::config('short', array(
    'engine' => 'File',
    'duration' => '+1 hours',
    'path' => CACHE,
    'prefix' => 'cake_short_'
));

// long
Cache::config('long', array(
    'engine' => 'File',
    'duration' => '+1 week',
    'probability' => 100,
    'path' => CACHE . 'long' . DS,
));

By placing the above code in your app/Config/bootstrap.php you will have two additional Cache configurations. The name of these configurations ‘short’ or ‘long’ is used as the $config parameter for Cache::write() and Cache::read().

Note

When using the FileEngine you might need to use the mask option to ensure cache files are made with the correct permissions.

New in version 2.4: In debug mode missing directories will now be automatically created to avoid unnecessary errors thrown when using the FileEngine.

Creating a storage engine for Cache

You can provide custom Cache adapters in app/Lib as well as in plugins using $plugin/Lib. App/plugin cache engines can also override the core engines. Cache adapters must be in a cache directory. If you had a cache engine named MyCustomCacheEngine it would be placed in either app/Lib/Cache/Engine/MyCustomCacheEngine.php as an app/libs or in $plugin/Lib/Cache/Engine/MyCustomCacheEngine.php as part of a plugin. Cache configs from plugins need to use the plugin dot syntax.:

Cache::config('custom', array(
    'engine' => 'CachePack.MyCustomCache',
    // ...
));

Note

App and Plugin cache engines should be configured in app/Config/bootstrap.php. If you try to configure them in core.php they will not work correctly.

Custom Cache engines must extend CacheEngine which defines a number of abstract methods as well as provides a few initialization methods.

The required API for a CacheEngine is

class CacheEngine

The base class for all cache engines used with Cache.

CacheEngine::write($key, $value, $config = 'default')
Returns:boolean for success.

Write value for a key into cache, optional string $config specifies configuration name to write to.

CacheEngine::read($key, $config = 'default')
Returns:The cached value or false for failure.

Read a key from the cache, optional string $config specifies configuration name to read from. Return false to indicate the entry has expired or does not exist.

CacheEngine::delete($key, $config = 'default')
Returns:Boolean true on success.

Delete a key from the cache, optional string $config specifies configuration name to delete from. Return false to indicate that the entry did not exist or could not be deleted.

CacheEngine::clear($check)
Returns:Boolean true on success.

Delete all keys from the cache. If $check is true, you should validate that each value is actually expired.

CacheEngine::clearGroup($group)
Returns:Boolean true on success.

Delete all keys from the cache belonging to the same group.

CacheEngine::decrement($key, $offset = 1)
Returns:Boolean true on success.

Decrement a number under the key and return decremented value

CacheEngine::increment($key, $offset = 1)
Returns:Boolean true on success.

Increment a number under the key and return incremented value

CacheEngine::gc()

Not required, but used to do clean up when resources expire. FileEngine uses this to delete files containing expired content.

Using Cache to store common query results

You can greatly improve the performance of your application by putting results that infrequently change, or that are subject to heavy reads into the cache. A perfect example of this are the results from Model::find(). A method that uses Cache to store results could look like:

class Post extends AppModel {

    public function newest() {
        $result = Cache::read('newest_posts', 'long');
        if (!$result) {
            $result = $this->find('all', array('order' => 'Post.updated DESC', 'limit' => 10));
            Cache::write('newest_posts', $result, 'long');
        }
        return $result;
    }
}

You could improve the above code by moving the cache reading logic into a behavior, that read from the cache, or ran the associated model method. That is an exercise you can do though.

As of 2.5 you can accomplish the above much more simply using Cache::remember(). Assuming you are using PHP 5.3 or newer, using the remember() method would look like:

class Post extends AppModel {

    public function newest() {
        $model = $this;
        return Cache::remember('newest_posts', function() use ($model){
            return $model->find('all', array(
                'order' => 'Post.updated DESC',
                'limit' => 10
            ));
        }, 'long');
    }
}

Using Cache to store counters

Counters for various things are easily stored in a cache. For example, a simple countdown for remaining ‘slots’ in a contest could be stored in Cache. The Cache class exposes atomic ways to increment/decrement counter values in an easy way. Atomic operations are important for these values as it reduces the risk of contention, and ability for two users to simultaneously lower the value by one, resulting in an incorrect value.

After setting an integer value, you can manipulate it using Cache::increment() and Cache::decrement():

Cache::write('initial_count', 10);

// Later on
Cache::decrement('initial_count');

// or
Cache::increment('initial_count');

Note

Incrementing and decrementing do not work with FileEngine. You should use APC, Redis or Memcached instead.

Using groups

New in version 2.2.

Sometimes you will want to mark multiple cache entries to belong to a certain group or namespace. This is a common requirement for mass-invalidating keys whenever some information changes that is shared among all entries in the same group. This is possible by declaring the groups in cache configuration:

Cache::config('site_home', array(
    'engine' => 'Redis',
    'duration' => '+999 days',
    'groups' => array('comment', 'post')
));

Let’s say you want to store the HTML generated for your homepage in cache, but would also want to automatically invalidate this cache every time a comment or post is added to your database. By adding the groups comment and post, we have effectively tagged any key stored into this cache configuration with both group names.

For instance, whenever a new post is added, we could tell the Cache engine to remove all entries associated to the post group:

// Model/Post.php

public function afterSave($created, $options = array()) {
    if ($created) {
        Cache::clearGroup('post', 'site_home');
    }
}

New in version 2.4.

Cache::groupConfigs() can be used to retrieve mapping between group and configurations, i.e.: having the same group:

// Model/Post.php

/**
 * A variation of previous example that clears all Cache configurations
 * having the same group
 */
public function afterSave($created, $options = array()) {
    if ($created) {
        $configs = Cache::groupConfigs('post');
        foreach ($configs['post'] as $config) {
            Cache::clearGroup('post', $config);
        }
    }
}

Groups are shared across all cache configs using the same engine and same prefix. If you are using groups and want to take advantage of group deletion, choose a common prefix for all your configs.

Cache API

class Cache

The Cache class in CakePHP provides a generic frontend for several backend caching systems. Different Cache configurations and engines can be set up in your app/Config/core.php

static Cache::config($name = null, $settings = array())

Cache::config() is used to create additional Cache configurations. These additional configurations can have different duration, engines, paths, or prefixes than your default cache config.

static Cache::read($key, $config = 'default')

Cache::read() is used to read the cached value stored under $key from the $config. If $config is null the default config will be used. Cache::read() will return the cached value if it is a valid cache or false if the cache has expired or doesn’t exist. The contents of the cache might evaluate false, so make sure you use the strict comparison operators: === or !==.

For example:

$cloud = Cache::read('cloud');

if ($cloud !== false) {
    return $cloud;
}

// generate cloud data
// ...

// store data in cache
Cache::write('cloud', $cloud);
return $cloud;
static Cache::write($key, $value, $config = 'default')

Cache::write() will write a $value to the Cache. You can read or delete this value later by referring to it by $key. You may specify an optional configuration to store the cache in as well. If no $config is specified, default will be used. Cache::write() can store any type of object and is ideal for storing results of model finds:

if (($posts = Cache::read('posts')) === false) {
    $posts = $this->Post->find('all');
    Cache::write('posts', $posts);
}

Using Cache::write() and Cache::read() to easily reduce the number of trips made to the database to fetch posts.

static Cache::delete($key, $config = 'default')

Cache::delete() will allow you to completely remove a cached object from the Cache store.

static Cache::set($settings = array(), $value = null, $config = 'default')

Cache::set() allows you to temporarily override a cache config’s settings for one operation (usually a read or write). If you use Cache::set() to change the settings for a write, you should also use Cache::set() before reading the data back in. If you fail to do so, the default settings will be used when the cache key is read.:

Cache::set(array('duration' => '+30 days'));
Cache::write('results', $data);

// Later on

Cache::set(array('duration' => '+30 days'));
$results = Cache::read('results');

If you find yourself repeatedly calling Cache::set() then perhaps you should create a new Cache::config(). This will remove the need to call Cache::set().

static Cache::increment($key, $offset = 1, $config = 'default')

Atomically increment a value stored in the cache engine. Ideal for modifying counters or semaphore type values.

static Cache::decrement($key, $offset = 1, $config = 'default')

Atomically decrement a value stored in the cache engine. Ideal for modifying counters or semaphore type values.

static Cache::clear($check, $config = 'default')

Destroy all cached values for a cache configuration. In engines like Apc, Memcache and Wincache, the cache configuration’s prefix is used to remove cache entries. Make sure that different cache configurations have different prefixes.

Cache::clearGroup($group, $config = 'default')
Returns:Boolean true on success.

Delete all keys from the cache belonging to the same group.

static Cache::gc($config)

Garbage collects entries in the cache configuration. This is primarily used by FileEngine. It should be implemented by any Cache engine that requires manual eviction of cached data.

static Cache::groupConfigs($group = null)
Returns:Array of groups and its related configuration names.

Retrieve group names to config mapping.

static Cache::remember($key, $callable, $config = 'default')

Provides an easy way to do read-through caching. If the cache key exists it will be returned. If the key does not exist, the callable will be invoked and the results stored in the cache at the provided key.

For example, you often want to cache query results. You could use remember() to make this simple. Assuming you are using PHP 5.3 or newer:

class Articles extends AppModel {
    function all() {
        $model = $this;
        return Cache::remember('all_articles', function() use ($model){
            return $model->find('all');
        });
    }
}

New in version 2.5: remember() was added in 2.5.