understand MongoDB cache system

Question

This is a basic question, but very important, and i am not sure to really get the point.

On the official documentation we can read

MongoDB ke

Answer 1

MongoDB attempts to keep entire collections in memory: it memory-maps each collection page. For everything to be in memory, both the data pages, and the indices that reference them, must be kept in memory.

If MongoDB returns a record, you can rest assured that it is now in memory (whether it was before your query or not).

MongoDB doesn't keep a "cache" of records in the same way that, say, a web browser does. When you commit a change, both the memory and the disk are updated.

Mongo is great when matched to the appropriate use cases. It is very high performance if you have sufficient server memory to cache everything, and declines rapidly past that point. Many, many high-volume websites use MongoDB: it's a good thing that memory is so cheap, now.