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Recovery and Atomicity

 

Log Records: The ‘Log File’ is used to record the database modifications. The log file is a sequence of the ‘log records’, recording all the update activities in the database.

 

The components of Log Record :

(a) Transaction Identifier: It is the unique identifier of the transaction that performed the ‘write’ operation.

 

(b) Data-item Identifier: It is the unique identifier of the data item written.

 

(c) OldValue: It is the value of the data item prior to the ‘write’.

 

(d) New-Value: It is the value that the data item will have after

 ‘write’ operation.

There are three types of log records :

< Ti start>  :  Transaction Ti has started.

< Ti commt> :   Transaction Ti has committed.

< Ti abort > : Transaction Ti has aborted.

 

Reference Link

Recovery and Atomicity