单阶段和两阶段（XA）提交之间的真正区别

Could someone clarify the difference between one-phase and two-phase commit. As far as I understand one-phase commit represents commit in the course of application server (Service method -> EntityManager) and XA commit is the same transaction up to the database (Service method -> EntityManager -> DB) and is used in order to properly rollback overall transaction. So why don't we use XA drivers by default? Is this just performance concern? Please correct me if I'm wrong.Could someone clarify the difference between on