A general mechanism to support nested atomic transactions

Nested atomic transactions focus increasing interest in the research area of distributed systems. The concept of nested transaction extends the traditional one transaction in that a nested transaction can contain any number of atomic (sub)transactions (nested in turn if more nesting levels are supponed). The nested transaction as a whole must still appear atomic, i.e. indivisibility and all-or-nothing properties must be guaranteed. We suggest to support nesting by exploiting a quite general synchronization mechanism based on the two-phase lock protocol. We reject the usual rule of maintaining objects locked until transaction completion and we allow early release of locks since the closure of the growing phase. This mechanism enhances potential concurrency between running transactions, but, on the other side, it requires heavier book-keeping and implies cascading aborts.