ch17 - Database System Concepts ©Silberschatz Korth and...

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Unformatted text preview: Database System Concepts ©Silberschatz, Korth and Sudarshan See www.db-book.com for conditions on re-use Chapter 17: Recovery System Chapter 17: Recovery System Version: Oct 5, 2006 ©Silberschatz, Korth and Sudarshan 17.<number> Database System Concepts, 5 th Ed. Chapter 17: Recovery System Chapter 17: Recovery System ■ Failure Classification ■ Storage Structure ■ Recovery and Atomicity ■ Log-Based Recovery ■ Shadow Paging ■ Recovery With Concurrent Transactions ■ Buffer Management ■ Failure with Loss of Nonvolatile Storage ■ Advanced Recovery Techniques ■ ARIES Recovery Algorithm ■ Remote Backup Systems ©Silberschatz, Korth and Sudarshan 17.<number> Database System Concepts, 5 th Ed. Failure Classification Failure Classification ■ Transaction failure : ● 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 (e.g., deadlock) ■ System crash : a power failure or other hardware or software failure causes the system to crash. ● Fail-stop assumption : non-volatile storage contents are assumed to not be corrupted by system crash Database systems have numerous integrity checks to prevent corruption of disk data ■ Disk failure : a head crash or similar disk failure destroys all or part of disk storage ● Destruction is assumed to be detectable: disk drives use checksums to detect failures ©Silberschatz, Korth and Sudarshan 17.<number> Database System Concepts, 5 th Ed. Recovery Algorithms Recovery Algorithms ■ Recovery algorithms are techniques to ensure database consistency and transaction atomicity and durability despite failures ● 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 ©Silberschatz, Korth and Sudarshan 17.<number> Database System Concepts, 5 th Ed. Storage Structure Storage Structure ■ Volatile storage : ● does not survive system crashes ● examples: main memory, cache memory ■ Nonvolatile storage : ● survives system crashes ● examples: disk, tape, flash memory, non-volatile (battery backed up) RAM ■ Stable storage : ● a mythical form of storage that survives all failures ● approximated by maintaining multiple copies on distinct nonvolatile media ©Silberschatz, Korth and Sudarshan 17.<number> Database System Concepts, 5 th Ed....
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ch17 - Database System Concepts ©Silberschatz Korth and...

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