Caching: How and when?

[CyanBook]

👋🏻 Hi, devs!

While I'm working on multiple features, I'm trying to improve the caching system as much as possible.

Aside from the schema itself, I was wondering whether it was better to use MongoDB (or any document DB) or Redis.
A Document DB allows data to be saved and never requested to Spotify again, but Redis is faster.

Also, some data in the saved requests can change (e.g album's popularity or artist's followers) - is a TTL necessary then?
This would make a document DB useless.

A combination of the two? Also, are there any other types and methods that need to be cached?
I'd like to hear your opinion about what's best for you and for this library's development.

Thanks for your time! 😄