Recovery - Recovery P.MIRUNALINI AP,CSE SSNCE Overview...

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Recovery P.MIRUNALINI AP,CSE SSNCE
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Overview s Transactions s Transaction Recovery s Write Ahead Log [WAL] Rule s ACID Properties s System Recovery s Checkpoint s Two Phase Commit [2PC]
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Database Recovery Purpose of Database Recovery s To bring the database into the last consistent state, which existed prior to the failure. s To preserve transaction properties (Atomicity, Consistency, Isolation and Durability).
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Recovery s Recovery in a database system means: restoring the database to a correct state after some failure has rendered the current state incorrect.
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Transactions s A transaction is a logical unit of work: s Begins with the execution of a BEGIN TRANSACTION s Ends with the execution of a COMMIT or ROLLBACK
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Transactions s If failure occurs before the transaction reaches its planned termination, then those updates will be undone . s The transaction either executes in its entirety or is totally canceled. s The transaction manager or transaction processing monitor [TP monitor] provides this atomicity
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s The commit operation signals successful end-of-transaction: s the database is in a correct state s all the updates made by the transaction can be committed s The rollback operation signals unsuccessful end-of- transaction: s the database might be in an incorrect state s all the updates made by the transaction must be undone s Recovery log : s Log file on which details of all updates – before and after each update are recorded.
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Recovery - Recovery P.MIRUNALINI AP,CSE SSNCE Overview...

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