Nitpicky terminology choices aside, this is a very good, easy-to-follow writeup on multi-region data system design. Understanding that the trick is shuffling around the latency makes it much easier to reason about where you want to focus your latency savings. One thing I wasn't quite sure on, though, is why Database A would care if Database B had a read of a certain kind (vs. a write). Reads don't change state, so if a million reads occur with no writes, the data should still be consistent, no?