COMP 266 Lecture Notes - Lecture 9: Recovery Approach, Database Administrator, Transaction Log
1 Jul 2018
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Question: Suggest an appropriate recovery
technique that a d...
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Suggest an appropriate recovery technique that a database administrator could use to resolve
each of the following situations.
a. A network disconnection occurs while a user is entering a transaction at an ATM bank
machine.
b. A disk drive fails during regular operations while a clerk is entering data about newly
registered students.
c. The registration office at a university entered an incorrect amount for a student tuition
payment. The error was discovered by the financial services department several weeks later.
d. The database administrator of a financial institution performed a full database backup, but
forgot to activate the journalizing facility. Afterwards, data entry clerks at the financial
institution entered transactions for two hours before the database became corrupt. It is discovered
that the journalizing facility of the database has not been activated since the backup was made.
Expert Answer
a) Aborted Transaction. Use Backward recovery . The transaction can be reapplied if
necessary or if the intent was to abort the transaction, then the rollback resolves all issues.
b) Database Destruction. Forward Recovery (using a backup copy of database) .If the
database is destroyed, e.g. a server catches fire or a disk drive crashes, then forward
recovery from the last good backup can be used to restore.
c) Incorrect data. If incorrect data is entered into the system, several approaches can be
used to correct the data errors including:
obackward recovery if the error is found soon.
orestart from checkpoint - rolls forward to the point of the error from the last good
checkpoint that was taken.
and reprocessing the transactions to the latest
d) Switching Recovery model : You can switch from any recovery model to another
recovery model, but prior to or after the switch, you may need to issue additional
transaction log or full backups to ensure you have a complete backup set.
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Document Summary
Question: suggest an appropriate recovery technique that a d The error was discovered by the financial services department several weeks later: the database administrator of a financial institution performed a full database backup, but forgot to activate the journalizing facility. Afterwards, data entry clerks at the financial institution entered transactions for two hours before the database became corrupt. It is discovered that the journalizing facility of the database has not been activated since the backup was made. The transaction can be reapplied if necessary or if the intent was to abort the transaction, then the rollback resolves all issues: database destruction. Forward recovery (using a backup copy of database) . if the database is destroyed, e. g. a server catches fire or a disk drive crashes, then forward recovery from the last good backup can be used to restore: incorrect data.
