- Semi-distributed because there's always a master coordinator for a given 2PC transaction. Because there are so few datacenters you tend to go through the same set of master coordinators.
- It's synchronous. All transactions are serialized through that master which kills your throughput and increases latency.
- Never serious considered this option because write throughput is very important to them. No single point of failure or serialization point would work for them. Latency is high because of the extra coordination. Writes can be in the 200msec area.
- This option does work though. You write to all datacenters or nothing. You get strong consistency and transactions.
- Need N+1 datacenters. If you take one down then you still have N to handle your load.
