Autonomous versus Nested Transactions
Though an autonomous transaction is started by the other transaction, it is not a nested transaction for the reasons shown below:
(i) It does not share the transactional resources (like locks) with the major transaction.
(ii)It does not depend on the major transaction. For illustration, if the major transaction rolls back, nested transactions roll back, while the autonomous transactions do not.
(iii)Its committed changes are visible to other transactions instantly. Whereas the nested transaction's committed changes are not visible to other transactions till the major transaction commits.