Design of the checkin service
Making a service that is radically simple and reliable
The critical insight is that a service collecting (timestamp, uuid)
pairs that only cares about the most recent timestamp for a given UUID is actually maintaining a crdt. All that work that databases need to do in order to prevent conflicting updates just goes out the window, and we can create a database that can be run in parallel with multiple masters without having to worry about the CAP theorem.