ch17 - Chapter 17: Recovery System Chapter Database System...

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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
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©Silberschatz, Korth and Sudarshan 17.2 Database System Concepts, 5 th Edition, Oct 5, 2006 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
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©Silberschatz, Korth and Sudarshan 17.3 Database System Concepts, 5 th Edition, Oct 5, 2006 Failure Classification Failure Classification ± Transaction failure : z Logical errors : transaction cannot complete due to some internal error condition z 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. z 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 z Destruction is assumed to be detectable: disk drives use checksums to detect failures
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©Silberschatz, Korth and Sudarshan 17.4 Database System Concepts, 5 th Edition, Oct 5, 2006 Recovery Algorithms Recovery Algorithms ± Recovery algorithms are techniques to ensure database consistency and transaction atomicity and durability despite failures z 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
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©Silberschatz, Korth and Sudarshan 17.5 Database System Concepts, 5 th Edition, Oct 5, 2006 Storage Structure Storage Structure ± Volatile storage : z does not survive system crashes z examples: main memory, cache memory ± Nonvolatile storage : z survives system crashes z examples: disk, tape, flash memory, non-volatile (battery backed up) RAM ± Stable storage : z a mythical form of storage that survives all failures z approximated by maintaining multiple copies on distinct nonvolatile media
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©Silberschatz, Korth and Sudarshan 17.6 Database System Concepts, 5 th Edition, Oct 5, 2006 Stable Stable - - Storage Implementation Storage Implementation ± Maintain multiple copies of each block on separate disks z copies can be at remote sites to protect against disasters such as fire or flooding.
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ch17 - Chapter 17: Recovery System Chapter Database System...

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