I should add that when you don't serialize cross-partition transactions, you have the hard problem of system recovery - transaction coordinators need to reach consensus on a consistent set of transactions to recover. Here's NDB's protocol for doing so: NDB’s solution to this problem was only published this year in Mikael Ronstrom's book on MySQL Cluster : https://drive.google.com/file/d/1gAYQPrWCTEhgxP8dQ8XLwMrwZPc...