This is a good explanation of how it happens on a single node. What do you do when the transaction is distributed? How do you achieve consensus? Is there a write up on it anywhere?
I don't know that there's been an exhaustive writeup of that part, but maybe one of us or somebody on the Apple team will put something together. It probably won't fit in an HN comment though!
Or... maybe this is the part where I point out that the product is now open-source, and invite you to read the (mostly very well commented) code. :-)
Going forward as an opensource product, I hope to see some clarity on the "how it works"... Distributed, performant ACID sounds good, almost too good to be true. Not that I doubt it at the moment, I just want to understand it better :)