Discuss deferred update technique of recovery.  What are the advantages?

 Ans:  The deferred update methods do not physically update the database on disk till after a transaction reaches its commit point; after that the updates are recorded in the database. Alternatively, deferred update methods postpone any actual updating of the database on disk until a transaction arrives its commit point. The transaction force-writes the log to disk previous to recording the updates in the database

Advantages:

• If a transaction fails previous to reaching its commit point, it will not have modified the database in any way, so UNDO is not required. Deferred update can lead to a recovery algorithm termed as NO-UNDO/REDO.
• This approach, while used with specific concurrency control methods, is designed never to need transaction rollback, and recovery simply contains redoing the operations of transactions committed after the last checkpoint from the log.