MongoDB querying performance for over 5 million records

Question

We\'ve recently hit the >2 Million records for one of our main collections and now we started to suffer for major performance issues on that collection.

They documen

Answer 1

If you are using $in, mongodb never uses INDEX. Change your query, by removing this $in. It should use index and it would give better performance than what you got earlier.

http://docs.mongodb.org/manual/core/query-optimization/