How to speed up MongoDb data fetching?

Question

MongoDB

The situation is as follows, there is a collection with 4.5 million documents. According to these documents, it is necessary to make a selection, mostly constant queries - select the last 100 documents, sort by a specific field and return 50 documents, etc.
The indexing of the fields on which the selection passes is carried out, but the operation time is 9-14 seconds.
Question:
How to implement query caching? How to properly optimize the database to minimize the time it takes to return the necessary data?

Answer 1

Look at explain requests. It looks like the indexes are not optimally created.