Do I understand the principle of using Redis correctly?

Question

Redis

Hello!
I understood the purpose of Redis as something like this:
If I have a large database, let's say 10 million users and each can have about 100 friends, then the friends table in mysql will contain 1 billion records.
For example, I need to select a feed of 500 users, and also display the value of whether the user is my friend. It turns out that JOINing records from a database with a billion records is hard for MySql. Therefore, we create in radish a copy of the friends table from the mysql database. And every time we remove or add a friend. We have to update the entry in both mysql and redis.
Well, then we work only with redis.
Please correct me if wrong

Answer 1

I misunderstood, but about friends, not this database at all,
see graph ones
, but radish, yes, it’s more efficient than just a muscle cache in terms of access speed