This chapter covers failure models and a variety of failure recovery techniques. Re-covery in a real-life database systems supporting concurrent transactions is rather complicated. To help the student understand concepts better, the chapter presents re-covery models in increasing degree of complexity. The chapter starts with a simple model for recovery, ignoring the issue of concurrency. Later, the model is extended to handle concurrent transactions with strict two-phase locking. | Chapter 17: Recovery System Version: Oct 5, 2006 Database System Concepts ©Silberschatz, Korth and Sudarshan See for conditions on reuse Chapter 17: Recovery System s Failure Classification s Storage Structure s Recovery and Atomicity s LogBased Recovery s Shadow Paging s Recovery With Concurrent Transactions s Buffer Management s Failure with Loss of Nonvolatile Storage s Advanced Recovery Techniques s ARIES Recovery Algorithm s Remote Backup Systems Database System Concepts, 5th Ed. 17. ©Silberschatz, Korth and Sudarshan Failure Classification s Transaction failure : q q Logical errors: transaction cannot complete due to some internal error condition System errors: the database system must terminate an active transaction due to an error condition (., deadlock) s System crash: a power failure or other hardware or software failure causes the system to crash. q Failstop assumption: nonvolatile storage contents are assumed to not be corrupted by system crash Database systems have numerous integrity checks to prevent corruption of disk data s Disk failure: a head crash or similar disk failure destroys all or part of disk storage q Destruction is assumed to be detectable: disk drives use checksums to detect failures Database System Concepts, 5th Ed. 17. ©Silberschatz, Korth and Sudarshan Recovery Algorithms s Recovery algorithms are techniques to ensure database consistency and transaction atomicity and durability despite failures q s Focus of this chapter Recovery algorithms have two parts 1. Actions taken during normal transaction processing to ensure enough information exists to recover from failures 2. Actions taken after a failure to recover the database contents to a state that ensures atomicity, consistency and durability Database System Concepts, 5th Ed. 17. ©Silberschatz, Korth and Sudarshan Storage Structure s .
