Tunable concurrency control for the number of incoming requests would have been good - before they even hit mongo. Then you can just dial things down a bit (ma

Tunable concurrency control for the number of incoming requests would have been good - before they even hit mongo. Then you can just dial things down a bit (making customers wait a bit) and let the system recover, and tune things back to the point of optimal behaviour, rather than letting things overload. (You set your concurrency limits at a point where you know the system is just beginning to slow down but is still performing satisfactorily)