Traditionally, relational databases were designed for scale-up architectures. In other words, to handle more load you get a bigger box. A few years ago this meant that to support a scale-out architecture you either ditched SQL or applied tricks like sharding and explicit active-passive replication. If you wanted a real ACID programming model against a flexible, logical database you were out of luck. This tension is what inspired the NewSQL movement and captures the heart of what NuoDB is all about.