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Cache

Using a cache is a great way of making your application run quicker. The Symfony cache component ships with many adapters to different storages. Every adapter is developed for high performance.

The following example shows a typical usage of the cache:

use Symfony\Contracts\Cache\ItemInterface;

// The callable will only be executed on a cache miss.
$value = $pool->get('my_cache_key', function (ItemInterface $item): string {
    $item->expiresAfter(3600);

    // ... do some HTTP request or heavy computations
    $computedValue = 'foobar';

    return $computedValue;
});

echo $value; // 'foobar'

// ... and to remove the cache key
$pool->delete('my_cache_key');

Symfony supports Cache Contracts and PSR-6/16 interfaces. You can read more about these at the component documentation </components/cache>.

Configuring Cache with FrameworkBundle

When configuring the cache component there are a few concepts you should know of:

Pool

This is a service that you will interact with. Each pool will always have its own namespace and cache items. There is never a conflict between pools.

Adapter

An adapter is a template that you use to create pools.

Provider

A provider is a service that some adapters use to connect to the storage. Redis and Memcached are examples of such adapters. If a DSN is used as the provider then a service is automatically created.

There are two pools that are always enabled by default. They are cache.app and cache.system. The system cache is used for things like annotations, serializer, and validation. The cache.app can be used in your code. You can configure which adapter (template) they use by using the app and system key like:

# config/packages/cache.yaml
framework:
    cache:
        app: cache.adapter.filesystem
        system: cache.adapter.system
<!-- config/packages/cache.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd"
>
    <framework:config>
        <framework:cache
            app="cache.adapter.filesystem"
            system="cache.adapter.system"
        />
    </framework:config>
</container>
// config/packages/cache.php
use Symfony\Config\FrameworkConfig;

return static function (FrameworkConfig $framework): void {
    $framework->cache()
        ->app('cache.adapter.filesystem')
        ->system('cache.adapter.system')
    ;
};

Tip

While it is possible to reconfigure the system cache, it's recommended to keep the default configuration applied to it by Symfony.

The Cache component comes with a series of adapters pre-configured:

  • cache.adapter.apcu </components/cache/adapters/apcu_adapter>
  • cache.adapter.array </components/cache/adapters/array_cache_adapter>
  • cache.adapter.doctrine_dbal </components/cache/adapters/doctrine_dbal_adapter>
  • cache.adapter.filesystem </components/cache/adapters/filesystem_adapter>
  • cache.adapter.memcached </components/cache/adapters/memcached_adapter>
  • cache.adapter.pdo </components/cache/adapters/pdo_adapter>
  • cache.adapter.psr6 </components/cache/adapters/proxy_adapter>
  • cache.adapter.redis </components/cache/adapters/redis_adapter>
  • cache.adapter.redis_tag_aware <redis-tag-aware-adapter> (Redis adapter optimized to work with tags)

Note

There's also a special cache.adapter.system adapter. It's recommended to use it for the system cache <cache-app-system>. This adapter uses some logic to dynamically select the best possible storage based on your system (either PHP files or APCu).

Some of these adapters could be configured via shortcuts.

# config/packages/cache.yaml
framework:
    cache:
        directory: '%kernel.cache_dir%/pools' # Only used with cache.adapter.filesystem

        default_doctrine_dbal_provider: 'doctrine.dbal.default_connection'
        default_psr6_provider: 'app.my_psr6_service'
        default_redis_provider: 'redis://localhost'
        default_memcached_provider: 'memcached://localhost'
        default_pdo_provider: 'pgsql:host=localhost'
<!-- config/packages/cache.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd"
>
    <framework:config>
        <!-- "directory" attribute is only used with cache.adapter.filesystem -->
        <framework:cache directory="%kernel.cache_dir%/pools"
            default-doctrine-dbal-provider="doctrine.dbal.default_connection"
            default-psr6-provider="app.my_psr6_service"
            default-redis-provider="redis://localhost"
            default-memcached-provider="memcached://localhost"
            default-pdo-provider="pgsql:host=localhost"
        />
    </framework:config>
</container>
// config/packages/cache.php
use Symfony\Config\FrameworkConfig;

return static function (FrameworkConfig $framework): void {
    $framework->cache()
        // Only used with cache.adapter.filesystem
        ->directory('%kernel.cache_dir%/pools')

        ->defaultDoctrineDbalProvider('doctrine.dbal.default_connection')
        ->defaultPsr6Provider('app.my_psr6_service')
        ->defaultRedisProvider('redis://localhost')
        ->defaultMemcachedProvider('memcached://localhost')
        ->defaultPdoProvider('pgsql:host=localhost')
    ;
};

7.1

Using a DSN as the provider for the PDO adapter was introduced in Symfony 7.1.

Creating Custom (Namespaced) Pools

You can also create more customized pools:

# config/packages/cache.yaml
framework:
    cache:
        default_memcached_provider: 'memcached://localhost'

        pools:
            # creates a "custom_thing.cache" service
            # autowireable via "CacheInterface $customThingCache"
            # uses the "app" cache configuration
            custom_thing.cache:
                adapter: cache.app

            # creates a "my_cache_pool" service
            # autowireable via "CacheInterface $myCachePool"
            my_cache_pool:
                adapter: cache.adapter.filesystem

            # uses the default_memcached_provider from above
            acme.cache:
                adapter: cache.adapter.memcached

            # control adapter's configuration
            foobar.cache:
                adapter: cache.adapter.memcached
                provider: 'memcached://user:password@example.com'

            # uses the "foobar.cache" pool as its backend but controls
            # the lifetime and (like all pools) has a separate cache namespace
            short_cache:
                adapter: foobar.cache
                default_lifetime: 60
<!-- config/packages/cache.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd"
>
    <framework:config>
        <framework:cache default-memcached-provider="memcached://localhost">
            <!-- creates a "custom_thing.cache" service
                 autowireable via "CacheInterface $customThingCache"
                 uses the "app" cache configuration -->
            <framework:pool name="custom_thing.cache" adapter="cache.app"/>

            <!-- creates a "my_cache_pool" service
                 autowireable via "CacheInterface $myCachePool" -->
            <framework:pool name="my_cache_pool" adapter="cache.adapter.filesystem"/>

            <!-- uses the default_memcached_provider from above -->
            <framework:pool name="acme.cache" adapter="cache.adapter.memcached"/>

            <!-- control adapter's configuration -->
            <framework:pool name="foobar.cache" adapter="cache.adapter.memcached"
                provider="memcached://user:password@example.com"
            />

            <!-- uses the "foobar.cache" pool as its backend but controls
                 the lifetime and (like all pools) has a separate cache namespace -->
            <framework:pool name="short_cache" adapter="foobar.cache" default-lifetime="60"/>
        </framework:cache>
    </framework:config>
</container>
// config/packages/cache.php
use Symfony\Config\FrameworkConfig;

return static function (FrameworkConfig $framework): void {
    $cache = $framework->cache();
    $cache->defaultMemcachedProvider('memcached://localhost');

    // creates a "custom_thing.cache" service
    // autowireable via "CacheInterface $customThingCache"
    // uses the "app" cache configuration
    $cache->pool('custom_thing.cache')
        ->adapters(['cache.app']);

    // creates a "my_cache_pool" service
    // autowireable via "CacheInterface $myCachePool"
    $cache->pool('my_cache_pool')
        ->adapters(['cache.adapter.filesystem']);

    // uses the default_memcached_provider from above
    $cache->pool('acme.cache')
        ->adapters(['cache.adapter.memcached']);

     // control adapter's configuration
    $cache->pool('foobar.cache')
        ->adapters(['cache.adapter.memcached'])
        ->provider('memcached://user:password@example.com');

    $cache->pool('short_cache')
        ->adapters(['foobar.cache'])
        ->defaultLifetime(60);
};

Each pool manages a set of independent cache keys: keys from different pools never collide, even if they share the same backend. This is achieved by prefixing keys with a namespace that's generated by hashing the name of the pool, the name of the cache adapter class and a configurable seed <reference-cache-prefix-seed> that defaults to the project directory and compiled container class.

Each custom pool becomes a service whose service ID is the name of the pool (e.g. custom_thing.cache). An autowiring alias is also created for each pool using the camel case version of its name - e.g. custom_thing.cache can be injected automatically by naming the argument $customThingCache and type-hinting it with either Symfony\\Contracts\\Cache\\CacheInterface or Psr\Cache\CacheItemPoolInterface:

use Symfony\Contracts\Cache\CacheInterface;
// ...

// from a controller method
public function listProducts(CacheInterface $customThingCache): Response
{
    // ...
}

// in a service
public function __construct(private CacheInterface $customThingCache)
{
    // ...
}

Tip

If you need the namespace to be interoperable with a third-party app, you can take control over auto-generation by setting the namespace attribute of the cache.pool service tag. For example, you can override the service definition of the adapter:

# config/services.yaml
services:
    # ...

    app.cache.adapter.redis:
        parent: 'cache.adapter.redis'
        tags:
            - { name: 'cache.pool', namespace: 'my_custom_namespace' }
<!-- config/services.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd"
>
    <services>
        <!-- ... -->

        <service id="app.cache.adapter.redis" parent="cache.adapter.redis">
            <tag name="cache.pool" namespace="my_custom_namespace"/>
        </service>
    </services>
</container>
// config/services.php
namespace Symfony\Component\DependencyInjection\Loader\Configurator;

return function(ContainerConfigurator $container): void {
    $container->services()
        // ...

        ->set('app.cache.adapter.redis')
            ->parent('cache.adapter.redis')
            ->tag('cache.pool', ['namespace' => 'my_custom_namespace'])
    ;
};

Custom Provider Options

Some providers have specific options that can be configured. The RedisAdapter </components/cache/adapters/redis_adapter> allows you to create providers with the options timeout, retry_interval. etc. To use these options with non-default values you need to create your own \Redis provider and use that when configuring the pool.

# config/packages/cache.yaml
framework:
    cache:
        pools:
            cache.my_redis:
                adapter: cache.adapter.redis
                provider: app.my_custom_redis_provider

services:
    app.my_custom_redis_provider:
        class: \Redis
        factory: ['Symfony\Component\Cache\Adapter\RedisAdapter', 'createConnection']
        arguments:
            - 'redis://localhost'
            - { retry_interval: 2, timeout: 10 }
<!-- config/packages/cache.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd"
>
    <framework:config>
        <framework:cache>
            <framework:pool name="cache.my_redis"
                adapter="cache.adapter.redis"
                provider="app.my_custom_redis_provider"
            />
        </framework:cache>
    </framework:config>

    <services>
        <service id="app.my_custom_redis_provider" class="\Redis">
            <factory class="Symfony\Component\Cache\Adapter\RedisAdapter" method="createConnection"/>
            <argument>redis://localhost</argument>
            <argument type="collection">
                <argument key="retry_interval">2</argument>
                <argument key="timeout">10</argument>
            </argument>
        </service>
    </services>
</container>
// config/packages/cache.php
namespace Symfony\Component\DependencyInjection\Loader\Configurator;

use Symfony\Component\Cache\Adapter\RedisAdapter;
use Symfony\Component\DependencyInjection\ContainerBuilder;
use Symfony\Config\FrameworkConfig;

return static function (ContainerBuilder $container, FrameworkConfig $framework): void {
    $framework->cache()
        ->pool('cache.my_redis')
            ->adapters(['cache.adapter.redis'])
            ->provider('app.my_custom_redis_provider');

    $container->register('app.my_custom_redis_provider', \Redis::class)
        ->setFactory([RedisAdapter::class, 'createConnection'])
        ->addArgument('redis://localhost')
        ->addArgument([
            'retry_interval' => 2,
            'timeout' => 10
        ])
    ;
};

Creating a Cache Chain

Different cache adapters have different strengths and weaknesses. Some might be really quick but optimized to store small items and some may be able to contain a lot of data but are quite slow. To get the best of both worlds you may use a chain of adapters.

A cache chain combines several cache pools into a single one. When storing an item in a cache chain, Symfony stores it in all pools sequentially. When retrieving an item, Symfony tries to get it from the first pool. If it's not found, it tries the next pools until the item is found or an exception is thrown. Because of this behavior, it's recommended to define the adapters in the chain in order from fastest to slowest.

If an error happens when storing an item in a pool, Symfony stores it in the other pools and no exception is thrown. Later, when the item is retrieved, Symfony stores the item automatically in all the missing pools.

# config/packages/cache.yaml
framework:
    cache:
        pools:
            my_cache_pool:
                default_lifetime: 31536000  # One year
                adapters:
                  - cache.adapter.array
                  - cache.adapter.apcu
                  - {name: cache.adapter.redis, provider: 'redis://user:password@example.com'}
<!-- config/packages/cache.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd"
>
    <framework:config>
        <framework:cache>
            <framework:pool name="my_cache_pool"
                default-lifetime="31536000"> <!-- One year -->
                <framework:adapter name="cache.adapter.array"/>
                <framework:adapter name="cache.adapter.apcu"/>
                <framework:adapter name="cache.adapter.redis" provider="redis://user:password@example.com"/>
            </framework:pool>
        </framework:cache>
    </framework:config>
</container>
// config/packages/cache.php
use Symfony\Config\FrameworkConfig;

return static function (FrameworkConfig $framework): void {
    $framework->cache()
        ->pool('my_cache_pool')
            ->defaultLifetime(31536000) // One year
            ->adapters([
                'cache.adapter.array',
                'cache.adapter.apcu',
                ['name' => 'cache.adapter.redis', 'provider' => 'redis://user:password@example.com'],
            ])
    ;
};

Using Cache Tags

In applications with many cache keys it could be useful to organize the data stored to be able to invalidate the cache more efficiently. One way to achieve that is to use cache tags. One or more tags could be added to the cache item. All items with the same tag could be invalidated with one function call:

use Symfony\Contracts\Cache\ItemInterface;
use Symfony\Contracts\Cache\TagAwareCacheInterface;

class SomeClass
{
    // using autowiring to inject the cache pool
    public function __construct(
        private TagAwareCacheInterface $myCachePool,
    ) {
    }

    public function someMethod(): void
    {
        $value0 = $this->myCachePool->get('item_0', function (ItemInterface $item): string {
            $item->tag(['foo', 'bar']);

            return 'debug';
        });

        $value1 = $this->myCachePool->get('item_1', function (ItemInterface $item): string {
            $item->tag('foo');

            return 'debug';
        });

        // Remove all cache keys tagged with "bar"
        $this->myCachePool->invalidateTags(['bar']);
    }
}

The cache adapter needs to implement Symfony\\Contracts\\Cache\\TagAwareCacheInterface to enable this feature. This could be added by using the following configuration.

# config/packages/cache.yaml
framework:
    cache:
        pools:
            my_cache_pool:
                adapter: cache.adapter.redis
                tags: true
<!-- config/packages/cache.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd"
>
    <framework:config>
        <framework:cache>
            <framework:pool name="my_cache_pool"
                adapter="cache.adapter.redis"
                tags="true"
            />
        </framework:cache>
    </framework:config>
</container>
// config/packages/cache.php
use Symfony\Config\FrameworkConfig;

return static function (FrameworkConfig $framework): void {
    $framework->cache()
        ->pool('my_cache_pool')
            ->tags(true)
            ->adapters(['cache.adapter.redis'])
    ;
};

Tags are stored in the same pool by default. This is good in most scenarios. But sometimes it might be better to store the tags in a different pool. That could be achieved by specifying the adapter.

# config/packages/cache.yaml
framework:
    cache:
        pools:
            my_cache_pool:
                adapter: cache.adapter.redis
                tags: tag_pool
            tag_pool:
                adapter: cache.adapter.apcu
<!-- config/packages/cache.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd"
>
    <framework:config>
        <framework:cache>
            <framework:pool name="my_cache_pool"
                adapter="cache.adapter.redis"
                tags="tag_pool"
            />
            <framework:pool name="tag_pool" adapter="cache.adapter.apcu"/>
        </framework:cache>
    </framework:config>
</container>
// config/packages/cache.php
use Symfony\Config\FrameworkConfig;

return static function (FrameworkConfig $framework): void {
    $framework->cache()
        ->pool('my_cache_pool')
            ->tags('tag_pool')
            ->adapters(['cache.adapter.redis'])
    ;

    $framework->cache()
        ->pool('tag_pool')
            ->adapters(['cache.adapter.apcu'])
    ;
};

Note

The interface Symfony\\Contracts\\Cache\\TagAwareCacheInterface is autowired to the cache.app service.

Clearing the Cache

To clear the cache you can use the bin/console cache:pool:clear [pool] command. That will remove all the entries from your storage and you will have to recalculate all the values. You can also group your pools into "cache clearers". There are 3 cache clearers by default:

  • cache.global_clearer
  • cache.system_clearer
  • cache.app_clearer

The global clearer clears all the cache items in every pool. The system cache clearer is used in the bin/console cache:clear command. The app clearer is the default clearer.

To see all available cache pools:

$ php bin/console cache:pool:list

Clear one pool:

$ php bin/console cache:pool:clear my_cache_pool

Clear all custom pools:

$ php bin/console cache:pool:clear cache.app_clearer

Clear all cache pools:

$ php bin/console cache:pool:clear --all

Clear all cache pools except some:

$ php bin/console cache:pool:clear --all --exclude=my_cache_pool --exclude=another_cache_pool

Clear all caches everywhere:

$ php bin/console cache:pool:clear cache.global_clearer

Clear cache by tag(s):

# invalidate tag1 from all taggable pools
$ php bin/console cache:pool:invalidate-tags tag1

# invalidate tag1 & tag2 from all taggable pools
$ php bin/console cache:pool:invalidate-tags tag1 tag2

# invalidate tag1 & tag2 from cache.app pool
$ php bin/console cache:pool:invalidate-tags tag1 tag2 --pool=cache.app

# invalidate tag1 & tag2 from cache1 & cache2 pools
$ php bin/console cache:pool:invalidate-tags tag1 tag2 -p cache1 -p cache2

Encrypting the Cache

To encrypt the cache using libsodium, you can use the Symfony\\Component\\Cache\\Marshaller\\SodiumMarshaller.

First, you need to generate a secure key and add it to your secret store </configuration/secrets> as CACHE_DECRYPTION_KEY:

$ php -r 'echo base64_encode(sodium_crypto_box_keypair());'

Then, register the SodiumMarshaller service using this key:

# config/packages/cache.yaml

# ...
services:
    Symfony\Component\Cache\Marshaller\SodiumMarshaller:
        decorates: cache.default_marshaller
        arguments:
            - ['%env(base64:CACHE_DECRYPTION_KEY)%']
            # use multiple keys in order to rotate them
            #- ['%env(base64:CACHE_DECRYPTION_KEY)%', '%env(base64:OLD_CACHE_DECRYPTION_KEY)%']
            - '@.inner'
<!-- config/packages/cache.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <!-- ... -->

    <services>
        <service id="Symfony\Component\Cache\Marshaller\SodiumMarshaller" decorates="cache.default_marshaller">
            <argument type="collection">
                <argument>env(base64:CACHE_DECRYPTION_KEY)</argument>
                <!-- use multiple keys in order to rotate them -->
                <!-- <argument>env(base64:OLD_CACHE_DECRYPTION_KEY)</argument> -->
            </argument>
            <argument type="service" id=".inner"/>
        </service>
    </services>
</container>
// config/packages/cache.php
use Symfony\Component\Cache\Marshaller\SodiumMarshaller;
use Symfony\Component\DependencyInjection\ChildDefinition;
use Symfony\Component\DependencyInjection\Reference;

// ...
$container->setDefinition(SodiumMarshaller::class, new ChildDefinition('cache.default_marshaller'))
    ->addArgument(['env(base64:CACHE_DECRYPTION_KEY)'])
    // use multiple keys in order to rotate them
    //->addArgument(['env(base64:CACHE_DECRYPTION_KEY)', 'env(base64:OLD_CACHE_DECRYPTION_KEY)'])
    ->addArgument(new Reference('.inner'));

Caution

This will encrypt the values of the cache items, but not the cache keys. Be careful not to leak sensitive data in the keys.

When configuring multiple keys, the first key will be used for reading and writing, and the additional key(s) will only be used for reading. Once all cache items encrypted with the old key have expired, you can completely remove OLD_CACHE_DECRYPTION_KEY.

Computing Cache Values Asynchronously

The Cache component uses the probabilistic early expiration algorithm to protect against the cache stampede <cache_stampede-prevention> problem. This means that some cache items are elected for early-expiration while they are still fresh.

By default, expired cache items are computed synchronously. However, you can compute them asynchronously by delegating the value computation to a background worker using the Messenger component </components/messenger>. In this case, when an item is queried, its cached value is immediately returned and a Symfony\\Component\\Cache\\Messenger\\EarlyExpirationMessage is dispatched through a Messenger bus.

When this message is handled by a message consumer, the refreshed cache value is computed asynchronously. The next time the item is queried, the refreshed value will be fresh and returned.

First, create a service that will compute the item's value:

// src/Cache/CacheComputation.php
namespace App\Cache;

use Symfony\Contracts\Cache\ItemInterface;

class CacheComputation
{
    public function compute(ItemInterface $item): string
    {
        $item->expiresAfter(5);

        // this is just a random example; here you must do your own calculation
        return sprintf('#%06X', mt_rand(0, 0xFFFFFF));
    }
}

This cache value will be requested from a controller, another service, etc. In the following example, the value is requested from a controller:

// src/Controller/CacheController.php
namespace App\Controller;

use App\Cache\CacheComputation;
use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\Component\Routing\Attribute\Route;
use Symfony\Contracts\Cache\CacheInterface;
use Symfony\Contracts\Cache\ItemInterface;

class CacheController extends AbstractController
{
    #[Route('/cache', name: 'cache')]
    public function index(CacheInterface $asyncCache): Response
    {
        // pass to the cache the service method that refreshes the item
        $cachedValue = $asyncCache->get('my_value', [CacheComputation::class, 'compute'])

        // ...
    }
}

Finally, configure a new cache pool (e.g. called async.cache) that will use a message bus to compute values in a worker:

# config/packages/framework.yaml
framework:
    cache:
        pools:
            async.cache:
                early_expiration_message_bus: messenger.default_bus

    messenger:
        transports:
            async_bus: '%env(MESSENGER_TRANSPORT_DSN)%'
        routing:
            'Symfony\Component\Cache\Messenger\EarlyExpirationMessage': async_bus
<!-- config/packages/framework.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xmlns:framework="http://symfony.com/schema/dic/symfony"
   xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd"
>
    <framework:config>
        <framework:cache>
            <framework:pool name="async.cache" early-expiration-message-bus="messenger.default_bus"/>
        </framework:cache>

        <framework:messenger>
            <framework:transport name="async_bus">%env(MESSENGER_TRANSPORT_DSN)%</framework:transport>
            <framework:routing message-class="Symfony\Component\Cache\Messenger\EarlyExpirationMessage">
                <framework:sender service="async_bus"/>
            </framework:routing>
        </framework:messenger>
    </framework:config>
</container>
// config/framework/framework.php
use function Symfony\Component\DependencyInjection\Loader\Configurator\env;
use Symfony\Component\Cache\Messenger\EarlyExpirationMessage;
use Symfony\Config\FrameworkConfig;

return static function (FrameworkConfig $framework): void {
    $framework->cache()
        ->pool('async.cache')
            ->earlyExpirationMessageBus('messenger.default_bus');

    $framework->messenger()
        ->transport('async_bus')
            ->dsn(env('MESSENGER_TRANSPORT_DSN'))
        ->routing(EarlyExpirationMessage::class)
            ->senders(['async_bus']);
};

You can now start the consumer:

$ php bin/console messenger:consume async_bus

That's it! Now, whenever an item is queried from this cache pool, its cached value will be returned immediately. If it is elected for early-expiration, a message will be sent through to bus to schedule a background computation to refresh the value.