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 :)<p>I&#x27;m not one of those mongo bashers. I&#x27;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 &quot;problem&quot; 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.<p>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).