MySQL Challenge: 100k Connections
Personally I would say that the base design of the app is wrong if you have 100k direct connections => I would implement some kind of intermediate layer that caches and/or schedules DB connections by some sort of priority queue... .And "re-connect and repeat if the query is too slow" is probably a killer (basically a negative "feedback loop" which makes a system that has performance problems become even slower and slower and slower...).