Transaction processing system: Difference between revisions

Revision as of 20:04, 26 January 2007

Revision as of 13:28, 27 February 2007

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* Backup: A backup copy is usually produced at least once a day. It should be stored in a secure ___location, protected from damage and loss.

* Journal: A journal maintains an audit trail of transactions and database changes. Transaction logs and Database change logs are used, a transaction log records all the essential data for each transactions, including data values, time of transaction and temrinalterminal number. A database change log contains before and after copies of records that have been modified by transactions.

* Checkpoint: A checkpoint record contains necessary information to restart the system. These should be taken frequently, such as several times an hour. It is possible to resume processing from the most recent checkpoint when a failure occersoccurs with only a few minutes of processing work that needs to be repeated.

* Recovery Manager: A recovery manager is a program which restores the database to a correct condition which can restart the transaction processing.

Depending on how the system failed, there can be two different recovery procedures used. Generally, the procedures involesinvolves restoring data that has been collected from a backup device and then running the transaction processing again. Two types of recovery are ''backward recovery'' and ''forward recovery'':

* Backward recovery: used to [[undo]] unwanted changes to the database. It reverses the changes made by transactions which have been aborted. It involves the logic of reprocessing each transaction - which is very time consuming.