Gary Varga (5/12/2014)
There are but have been deemed too expensive and unnecessary for what NOSQL was originally intended for. Basically, it is a big misunderstanding with the people applying NOSQL paying too much attention to marketing and not enough to technical documentation.
It's not that they are too expensive or unnecessary, though that may be the decision at times.
It's that there is no way to do it at scale. If you get the volume of data that a Facebook or Twitter, or Google get, there is no way to get those machines in sync, physically. The laws of physics would be challenged, even if you were writing that data to memory.
When NoSQL says eventually consistent, it's not that they mean the data won't be the same until tomorrow, or an hour from now. They mean that not this ms. In practice, the consistency often is there sub-second, though it can be minutes when loads are high. It's the same with Service Broker. It doesn't make transactions instantaneous, but often it's so close that it might as well be instantaneous, in a practical sense, for most applications.