[ryzhyk]

The computational complexity of running an analytical query on a database is, at best, O(N), where N is the size of the database. The computational complexity of evaluating queries incrementally over streaming data with a well-designed query engine is O(delta), where delta is the size of the *new* data. If your use case is well served by a database (i.e., can tolerate the latency), then you're certainly better off relying on the more mature technology. But if you need to do some heavy-weight queries and get fresh results in real-time, no DB I can think of can pull that off (including "real-time" databases).