I can't speak for high performance/near or realtime system people but I would not trust a managed database service for those needs. My experience is that the managed offerings lag behind upstream versions substantially and usually are economical because they are multitenant. So you have a bit less predictability in io wait / cpu queue, lose host kernel level tunings (page sizes or hugepages, share memory allocation, etc), and - not naming names - some managed db services are so behind they lack critical query planner profiling features. That's not even going into application workload specific tuning for various nosql stores. This is a nice article but its audience is people that haven't scaled up a system but are trying to cope with success. It's not great generalized scaling advice.