When is it better to use mongodb and when is it better to use a relational database?

Question

MongoDB

What kind of data structure would be most useful for mongo db? And with what data structure should you categorically abandon Mongo and use a relational database?

Answer 1

The name of the storage type (key-value or noSQL) already hides part of the answer to the question. If there is a lot of data, but they are simple id-name type and complex selections are not needed, then key-value is also suitable. If you need a selection for complex conditions (id that have a balance of more than 100 but age less than 30 and only male), then take relational ones.
On Habré, battles are constantly going on these topics, I think that reading them (and especially the comments on them) will allow you to form your own opinion on this matter.
Are relational databases doomed?
Why you need to think 1000 times before using ...
Hedgehog with a snake in one basket

Answer 2

There seems to be almost no rationale for MongoDB right now. Postgres can do almost everything that Monga can, plus relays, constraints, transactions, functional indexes, and a bunch of everything. From the fact that Postgres does not seem to be able to do this bulk upsert yet.