I've only ever worked on small projects so I'm not at all familiar with these very high-scale distributed databases but from the post it seems to indicate that Spanner is in a league of its own because it integrated hardware into the mix where the others are software only. What are the differences in scale between the two categories mentioned?
Yes, Spanner is quite unusual in the distributed database world in how hardware is a pretty important part of their solution. Other systems may claim important integrations with hardware, but for Spanner, the architecture really relies on particular hardware assumptions.
To answer your question about scale: there is no real practical difference in scalability between the two categories discussed in the post. Partitioned consensus has better theoretical scalability, but I am not aware of any real-world workload that can not be handled by global consensus with batching.
I think this "global consensus with batching does everything partitioned does" is a very much theory vs practice type of statement. As in, in theory there is no difference between theory and practice :-)
I've seen those batched consensus systems, and honestly, you're kidding yourself if you think they can handle a million qps. Just transmit time of the data on ethernet would become an issue alone! Even with 40 gig - transmit time never becomes free. So now you're stuffing 1/10th of a million qps worth of data via a single set of machines (3, 5, 7, 9? Some relatively small amount)
