Right, it's either a trivial merge when you commit the transaction, or it's a conflict (i.e. two transactions updated the same attribute of the same entity). T

Right, it's either a trivial merge when you commit the transaction, or it's a conflict (i.e. two transactions updated the same attribute of the same entity). There's no automatically fixing a conflict so the second transaction fails. Since there's full isolation that's pretty standard optimistic locking: http://en.wikipedia.org/wiki/Optimistic_locking http://en.wikipedia.org/wiki/Optimistic_locking In most cases the transaction would succeed if it was automatically retried.