.. index:: single: Cache Pool single: APCu Cache single: Array Cache single: Chain Cache single: Doctrine Cache single: Filesystem Cache single: Memcached Cache single: PDO Cache, Doctrine DBAL Cache single: Redis Cache .. _component-cache-cache-pools: Cache Pools and Supported Adapters ================================== Cache Pools are the logical repositories of cache items. They perform all the common operations on items, such as saving them or looking for them. Cache pools are independent of the actual cache implementation. Therefore, applications can keep using the same cache pool even if the underlying cache mechanism changes from a file system based cache to a Redis or database based cache. .. _component-cache-creating-cache-pools: Creating Cache Pools -------------------- Cache Pools are created through the **cache adapters**, which are classes that implement both :class:`Symfony\\Contracts\\Cache\\CacheInterface` and ``Psr\Cache\CacheItemPoolInterface``. This component provides several adapters ready to use in your applications. .. toctree:: :glob: :maxdepth: 1 adapters/* Using the Cache Contracts ------------------------- The :class:`Symfony\\Contracts\\Cache\\CacheInterface` allows fetching, storing and deleting cache items using only two methods and a callback:: use Symfony\Component\Cache\Adapter\FilesystemAdapter; use Symfony\Contracts\Cache\ItemInterface; $cache = new FilesystemAdapter(); // The callable will only be executed on a cache miss. $value = $cache->get('my_cache_key', function (ItemInterface $item) { $item->expiresAfter(3600); // ... do some HTTP request or heavy computations $computedValue = 'foobar'; return $computedValue; }); echo $value; // 'foobar' // ... and to remove the cache key $cache->delete('my_cache_key'); Out of the box, using this interface provides stampede protection via locking and early expiration. Early expiration can be controlled via the third "beta" argument of the :method:`Symfony\\Contracts\\Cache\\CacheInterface::get` method. See the :doc:`/components/cache` article for more information. Early expiration can be detected inside the callback by calling the :method:`Symfony\\Contracts\\Cache\\ItemInterface::isHit` method: if this returns ``true``, it means we are currently recomputing a value ahead of its expiration date. For advanced use cases, the callback can accept a second ``bool &$save`` argument passed by reference. By setting ``$save`` to ``false`` inside the callback, you can instruct the cache pool that the returned value *should not* be stored in the backend. Using PSR-6 ----------- Looking for Cache Items ~~~~~~~~~~~~~~~~~~~~~~~ Cache Pools define three methods to look for cache items. The most common method is ``getItem($key)``, which returns the cache item identified by the given key:: use Symfony\Component\Cache\Adapter\FilesystemAdapter; $cache = new FilesystemAdapter('app.cache'); $latestNews = $cache->getItem('latest_news'); If no item is defined for the given key, the method doesn't return a ``null`` value but an empty object which implements the :class:`Symfony\\Component\\Cache\\CacheItem` class. If you need to fetch several cache items simultaneously, use instead the ``getItems([$key1, $key2, ...])`` method:: // ... $stocks = $cache->getItems(['AAPL', 'FB', 'GOOGL', 'MSFT']); Again, if any of the keys doesn't represent a valid cache item, you won't get a ``null`` value but an empty ``CacheItem`` object. The last method related to fetching cache items is ``hasItem($key)``, which returns ``true`` if there is a cache item identified by the given key:: // ... $hasBadges = $cache->hasItem('user_'.$userId.'_badges'); Saving Cache Items ~~~~~~~~~~~~~~~~~~ The most common method to save cache items is ``Psr\Cache\CacheItemPoolInterface::save``, which stores the item in the cache immediately (it returns ``true`` if the item was saved or ``false`` if some error occurred):: // ... $userFriends = $cache->getItem('user_'.$userId.'_friends'); $userFriends->set($user->getFriends()); $isSaved = $cache->save($userFriends); Sometimes you may prefer to not save the objects immediately in order to increase the application performance. In those cases, use the ``Psr\Cache\CacheItemPoolInterface::saveDeferred`` method to mark cache items as "ready to be persisted" and then call to ``Psr\Cache\CacheItemPoolInterface::commit`` method when you are ready to persist them all:: // ... $isQueued = $cache->saveDeferred($userFriends); // ... $isQueued = $cache->saveDeferred($userPreferences); // ... $isQueued = $cache->saveDeferred($userRecentProducts); // ... $isSaved = $cache->commit(); The ``saveDeferred()`` method returns ``true`` when the cache item has been successfully added to the "persist queue" and ``false`` otherwise. The ``commit()`` method returns ``true`` when all the pending items are successfully saved or ``false`` otherwise. Removing Cache Items ~~~~~~~~~~~~~~~~~~~~ Cache Pools include methods to delete a cache item, some of them or all of them. The most common is ``Psr\Cache\CacheItemPoolInterface::deleteItem``, which deletes the cache item identified by the given key (it returns ``true`` when the item is successfully deleted or doesn't exist and ``false`` otherwise):: // ... $isDeleted = $cache->deleteItem('user_'.$userId); Use the ``Psr\Cache\CacheItemPoolInterface::deleteItems`` method to delete several cache items simultaneously (it returns ``true`` only if all the items have been deleted, even when any or some of them don't exist):: // ... $areDeleted = $cache->deleteItems(['category1', 'category2']); Finally, to remove all the cache items stored in the pool, use the ``Psr\Cache\CacheItemPoolInterface::clear`` method (which returns ``true`` when all items are successfully deleted):: // ... $cacheIsEmpty = $cache->clear(); .. tip:: If the cache component is used inside a Symfony application, you can remove items from cache pools using the following commands (which reside within the :ref:`framework bundle `): To remove *one specific item* from the *given pool*: .. code-block:: terminal $ php bin/console cache:pool:delete # deletes the "cache_key" item from the "cache.app" pool $ php bin/console cache:pool:delete cache.app cache_key You can also remove *all items* from the *given pool(s)*: .. code-block:: terminal $ php bin/console cache:pool:clear # clears the "cache.app" pool $ php bin/console cache:pool:clear cache.app # clears the "cache.validation" and "cache.app" pool $ php bin/console cache:pool:clear cache.validation cache.app .. _component-cache-cache-pool-prune: Pruning Cache Items ------------------- Some cache pools do not include an automated mechanism for pruning expired cache items. For example, the :ref:`FilesystemAdapter ` cache does not remove expired cache items *until an item is explicitly requested and determined to be expired*, for example, via a call to ``Psr\Cache\CacheItemPoolInterface::getItem``. Under certain workloads, this can cause stale cache entries to persist well past their expiration, resulting in a sizable consumption of wasted disk or memory space from excess, expired cache items. This shortcoming has been solved through the introduction of :class:`Symfony\\Component\\Cache\\PruneableInterface`, which defines the abstract method :method:`Symfony\\Component\\Cache\\PruneableInterface::prune`. The :ref:`ChainAdapter `, :ref:`FilesystemAdapter `, :ref:`PdoAdapter `, and :ref:`PhpFilesAdapter ` all implement this new interface, allowing manual removal of stale cache items:: use Symfony\Component\Cache\Adapter\FilesystemAdapter; $cache = new FilesystemAdapter('app.cache'); // ... do some set and get operations $cache->prune(); The :ref:`ChainAdapter ` implementation does not directly contain any pruning logic itself. Instead, when calling the chain adapter's :method:`Symfony\\Component\\Cache\\Adapter\\ChainAdapter::prune` method, the call is delegated to all its compatible cache adapters (and those that do not implement ``PruneableInterface`` are silently ignored):: use Symfony\Component\Cache\Adapter\ApcuAdapter; use Symfony\Component\Cache\Adapter\ChainAdapter; use Symfony\Component\Cache\Adapter\FilesystemAdapter; use Symfony\Component\Cache\Adapter\PdoAdapter; use Symfony\Component\Cache\Adapter\PhpFilesAdapter; $cache = new ChainAdapter([ new ApcuAdapter(), // does NOT implement PruneableInterface new FilesystemAdapter(), // DOES implement PruneableInterface new PdoAdapter(), // DOES implement PruneableInterface new PhpFilesAdapter(), // DOES implement PruneableInterface // ... ]); // prune will proxy the call to PdoAdapter, FilesystemAdapter and PhpFilesAdapter, // while silently skipping ApcuAdapter $cache->prune(); .. tip:: If the cache component is used inside a Symfony application, you can prune *all items* from *all pools* using the following command (which resides within the :ref:`framework bundle `): .. code-block:: terminal $ php bin/console cache:pool:prune