public interface DBBackUpListener
The backup service listener Interface. The listener will notified when the
active DB transactions fully drained out and ready for the backup. The steps
for backup as below
1) Backup service initialize the backup
2) The persistence layer stop processing new DB write operations requests.
3) Finish off all the existing/active DB operations
4) Notify the backup listener the DB ready for backup
5) Backup process take over the control and start backup
6) Once backup over, inform persistence layer
7) Persistence layer start operate normally by processing DB operations.