Exploiting A History Database for Backup

Database systems provide media recovery by talcing periodic backups and applying a recovery log to a backup to r’estore the failed media. A transaction-time database is one that retains multiple versions of data, recording with each version the time of the transaction that created it. Such a database provides access to historical versions based on transaction time, and permits reconstruction of timeslices representing the data that were valid at past times. This paper shows how a TSB-tree supported transaction-time database can also provide the backup function of media recovery. Thus, the same versions used for database history are used for database backup. The coat of taking a T.&%-tree backup is comparable to that of a conventional diflerential backup. The media recovery cost, especially when the media failure is partial, e.g. a single disk page, will usually be lower.