Improve explanation of cache.app and cache.system#15827

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Improve explanation of cache.app and cache.system#15827

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umulmrum commentedSep 17, 2021

This PR intends to clarify some things about cache.system and cache.app (#12774 among other things). Comments welcome of course :-)

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Sep 17, 2021

umulmrum changed the base branch from5.4 to4.4

September 17, 2021 14:56

umulmrum changed the title~~Improve explanation of cache.app and cache.system~~[Cache] Improve explanation of cache.app and cache.system

Sep 20, 2021

stof reviewed

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		The system cache ``cache.system`` is used for things like annotations,
		serializer, and validation. Usage is reserved for Symfony components
		and you should not use it for application cache needs.

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stofSep 20, 2021

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The application can also use it if it has its own data derived from the source code that can be generated during cache-warmup.

The rules for usingcache.system are:

the cached content does not need to change if the source code of the app does not change (i.e. it does not need to change between deployments)
the cached content has a CacheWarmer generating it (thecache.adapter.system is optimized for being read-only after the warm-up)

That's why it is used for the metadata of serializer and validation. But we could totally imagine applications that generate some metadata extracted from their source code (even though this is indeed more advanced use cases than the ones usingcache.app.

On the other hand,cache.app is independent from the deployment cycle of the source code (and generally needs to use a shared storage like Redis rather than the filesystem once you have multiple servers)