Processes that trigger a rollback, restoring a set of local checkpoints after detecting a failure, engage in a specialized rollback session, labelled with a rollback level.
They indicate a checkpoint level as the target of the rollback, under condition that processes that trigger the rollback also triggered a checkpoint with that checkpoint level.
If the application suggests that concurrent, conflicting rollbacks may arise, then it is appropriate to introduce a centralized registry, that will be invited in any rollback session.
Processes that enter a session with a higher rollback level will restore the local checkpoint labelled with the indicated checkpoint level upon entering the session.