[harel]

If your setup makes sense for you, its fine - stay with it. focus on real problem, not ones people on this thread think you have :)

I'm not one of those mongo bashers. I've used mongo before for the same purpose you do - time series statistical data along side a postgres db for everything else. And it worked fine for me. However, at that time postgresql was pre 9.4. Today I would have kept it all in postgres and simply archived older data if needed. And to be fair, its not even a "problem" until you need to filter by one data source and sort by the other. We had to be creative when we got to those problems.

As for my choice of Postgres over mySql - that is for 2 reasons - first being that postgres is not owned by Oracle, and second that postgres is more mature, feature rich and reliable than mysql (i.e., better).