It feels like they've snuck in an element of deterministic databases. This would explain why they don't take the penalty of the 2-phase commit round-trips. What's more interesting is how they've implemented this by just waiting for sufficient replica updates to appear in the database until they're confident in being strictly serializable. Of course, if those updates don't make it because of a network partition then the transaction will hang until it's over. Hopefully they really can count on there never being a network partition. Then again, a network partition would halt all related multi-homed transactions anyway so I guess it's a moot point.