NoSQL usage issues

  mongodb, question

After checking a lot of information, I was a little confused.
If Mongodb and Redis are used at the same time, will the functions repeat?
My personal idea is that Mongdb will be used as a database, and then Redis will cache Top10 hot data and Session.
But I read that Mongodb can also cache these. Then I was confused. Please advise.

Mongdb is right when the database is used, and then Redis is used to cache Top10 hot data and Session.

Mongodb when persistent database, redis do memory cache database