Thursday, 6 February 2020

Recovery System

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Recovery System


? The recovery mechanism is needed in database system to take care of failures.
? One Formatted: Centered can use either the log based or page based recovery schemes.
? Buffer management is an important issue for DBMS as it affects the process of recovery.
? Remote backup systems allow a copy of complete data.


Deferred database modification: The deferred database modification scheme records all the
modifications to the log, but defers all the writes to after partial commit.
Disk failure: A disk block loses its content as a result of either a head crash or failure during a
data transfer operation.
Immediate database modification: The immediate database modification scheme allows database
updates on the stored database even of an uncommitted transaction.
Log records: Log records are buffered in the main memory, instead of being output directly to a
stable storage media.
Recovery: Recovery algorithms are techniques to ensure database consistency and transaction
atomicity and durability despite failures.
Storage media: Storage media can be distinguished by their relative speed, capacity, and resilience
to failure, and classified as volatile storage or nonvolatile storage.
System crash: There is a hardware malfunction, or a bug in the database soft ware or the operating
system, that causes the loss of the content of volatile storage, and brings transaction processing
to a halt.

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