## 16.2. Behavior

An autonomous transaction can happen only inside another transaction. Inside an existing transaction (call it T0), the user can decide to start an autonomous transaction. Then T0 is paused and pushed in an autonomous transaction stack, and a new transaction (call it T1) is started.

At some point in the future the user can commit the autonomous transaction; after T1 is committed then T0 is popped from the autonomous transaction stack and resumed. The user can also decide to `COMMIT` the parent transaction T0, in which case T1 is committed, then T0 is popped from the autonomous transaction stack and then committed.

All the transactions happen synchronously; at any time only one transaction can be active, while in the stack there are zero (or more) paused transactions in the stack. All the possible combinations of `COMMIT` / `ROLLBACK` for T0 and T1 can happen; for instance, it is possible to COMMIT T1 and ROLLBACK T0. It is possible to nest autonomous transactions, up to a global resource limit (e.g. the autonomous transaction stack size) which can be set on the server.