I came across these databases:
1. Synchronized distributed cloud database https://www.firebase.com/how-it-works.html
3. Druid: http://www.github.com/metamx/druid
One Druid cluster currently exposes a data set of >40 billion rows of data representing >2 trillion impressions in hypercubes of varying dimensionality (largest is 30+ dimensions) while allowing for exploration using top lists and timeseries in sub-second latencies
Gokul's Blog 