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Configuring the Cache Service


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So... I want to know how I can configure the cache service... like to store the cache somewhere else. In the real world, we can just search for "How do I configure Symfony's cache service". But... we can also figure this out on our own, by using the commands we just learned.

We already noticed there's a cache.yaml file:

# Unique name of your app: used to compute stable namespaces for cache keys.
#prefix_seed: your_vendor_name/app_name
# The "app" cache stores to the filesystem by default.
# The data in this cache should persist between deploys.
# Other options include:
# Redis
#app: cache.adapter.redis
#default_redis_provider: redis://localhost
# APCu (not recommended with heavy random-write workloads as memory fragmentation can cause perf issues)
#app: cache.adapter.apcu
# Namespaced pools use the above "app" backend by default
#my.dedicated.cache: null

It looks like FrameworkBundle is responsible for creating the cache service... and it has a sub cache key where we can pass some values to control it. All of this is commented-out at the moment.

To get more information about FrameworkBundle, run:

php bin/console config:dump framework

FrameworkBundle is the main bundle inside of Symfony. So you can see that this dumps... wow... a ton. FrameworkBundle provides a lot of services... so there's a lot of config.

Debugging the Cache Config

To... zoom in a bit, re-run the command again, passing framework and then cache to filter for that sub-key:

php bin/console config:dump framework cache

And... cool! This may not always be super understandable, but it's a great starting point. This definitely just helped us answer the question:

Why does the cache system store stuff in the var/cache directory?

Because... there's a directory key that defaults to %kernel.cache_dir%... which is a fancy way of pointing at the /var/cache/dev directory. And then we see /pools/app, which is the actual directory that holds our cache.

Using dump() and the Profiler

So here's the goal: instead of caching things to the filesystem, I want to change the cache system to store somewhere else. Before we do that, go into VinylController and, so we can see the result of the change we're about to make, dump($cache). We've been using dd() so far, which stands for "dump and die". But in this case I want dump()... but let the page load.

52 lines | src/Controller/VinylController.php
// ... lines 1 - 12
class VinylController extends AbstractController
// ... lines 15 - 33
public function browse(HttpClientInterface $httpClient, CacheInterface $cache, string $slug = null): Response
// ... lines 36 - 37
// ... lines 39 - 49

Refresh now. Wait, where is my dump? This is a... feature! When you use dump(), you won't actually see it on the page: it hides down here on the web debug toolbar. If you look there, the cache is some sort of TraceableAdapter. But inside of that, there's an object called FilesystemAdapter. That's proof that the cache system is saving to the filesystem.

Configuring the Cache Adapter

To make this store somewhere else, go into cache.yaml and change this app key. You can set this to a number of different special strings, called adapters. If we wanted to store our cache in Redis, we would use cache.adapter.redis.

To make things really easy, use cache.adapter.array:

20 lines | config/packages/cache.yaml
// ... lines 3 - 10
app: cache.adapter.array
// ... lines 12 - 20

The array adapter is a fake cache where it does store things... but it only lives for the duration of the request. So, at the end of each request, it forgets everything. It's a fake cache, but it's enough to see how changing this key will affect the cache service itself.

Watch what happens. Currently, we have a FilesystemAdapter. When we refresh... the cache is an ArrayAdapter! And since the ArrayAdapter forgets its cache at the end of the request, you can see that every single request does now makes an HTTP request.

Takeaway: It's all about Controlling how Services are Instantiated

If you're a little confused by this, let me try to clear things up. The point of this chapter is not to teach you how to change this specific key in the cache file. Ultimately, if you need to configure something in Symfony, you'll just search the docs... which will tell you exactly what to do and which key to change.

Nope, the big takeaway is that the sole purpose of these config files is to configure the services in our app. Each time you change a key in any of these files, the end result is that you just changed how some service is instantiated. Tweaking a key may change the entire class name of a service object, like in this case, or it may change the 2nd or 3rd constructor argument that will be passed when the service is instantiated. It doesn't really matter what changes, as long as you realize that this config is all about services and how they're instantiated.

In fact, none of this config can be read directly from your app. You couldn't, for example, ask for the "cache" configuration from inside of a controller. Nope, Symfony reads this config, uses it to configure how each service object will be instantiated, then throws it away. Services are supreme.

Next, sometimes you'll need certain configuration to be different based on whether you're developing locally or running on production. Symfony has a system for this called "environments". Let's learn all about that.