{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Recovery - Chapter 17 Recovery System Chapter Database...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon
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
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
©Silberschatz, Korth and Sudarshan 17.2 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
Background image of page 2
©Silberschatz, Korth and Sudarshan 17.3 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
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
©Silberschatz, Korth and Sudarshan 17.4 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
Background image of page 4
©Silberschatz, Korth and Sudarshan 17.5 Database System Concepts, 5 th Ed. Stable-Storage Implementation Stable-Storage Implementation Maintain multiple copies of each block on separate disks copies can be at remote sites to protect against disasters such as fire or flooding. Failure during data transfer can still result in inconsistent copies: Block transfer can result in Successful completion Partial failure: destination block has incorrect information Total failure: destination block was never updated Protecting storage media from failure during data transfer (one solution): Execute output operation as follows (assuming two copies of each block): 1. Write the information onto the first physical block.
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 6
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}