Understanding the recovery task

Recovery is the task of restoring a failed system, application program, or database back to normal operations.

Recovery is the largest and most complex part of operations. For this reason, any discussion of operations is primarily a discussion of recovery.

Recovering a system can involve:

• Databases
• User requests to process data
• Programs that do the processing (application programs)
• Output sent to users

A recoverable system ensures:

• Data is not lost
• Incomplete changes to a database are not saved

Data can be lost in two ways. It can be physically lost—the disk or tape on which it resides can be damaged or misplaced. Or it can be logically lost—the data becomes incorrect or loses its relationship to other data. A system that ensures data integrity ensures that data cannot be lost or saved incompletely.