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Chapter 19: Problem 10

Discuss the UNDO and REDO operations and the recovery techniques that use each.

Short Answer

Expert verified
UNDO operation is used to revert the database to a previous state in case a transaction cannot be completed due to errors or system failures, whereas REDO operation is used after system failure to reapply the changes from committed transactions that have not been reflected in the database. The UNDO and REDO operations are crucial for maintaining data integrity and consistency in database systems.

Step by step solution

01

Definition of UNDO and REDO Operations

UNDO operations in a database management system are used to revert the database from its current state to a previous state. On the other hand, REDO operations are used to implement or reapply any modifications or updates that were undone due to failures or errors. They ensure the sequence of events is preserved, and the database reflects the correct state of the data.
02

Understanding Recovery Techniques using UNDO operations

The UNDO operation is used in recovery techniques when an error or system failure occurs during a transaction. If a transaction has made some changes but could not be completed due to some issues, an UNDO operation is used to roll back the changes made by the unfinished transaction, thus maintaining the data integrity.
03

Understanding Recovery Techniques using REDO operations

The REDO operation is used in recovery techniques after a system failure occurs. If a transaction had been committed successfully but the changes are not reflected in the database due to system failure, REDO operation is used to reapply the missing changes from the log, ensuring that all committed transactions are reflected in the database.

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Most popular questions from this chapter

What are log sequence numbers (LSNs) in ARIES? How are they used? What information does the Dirty Page Table and Transaction Table contain? Describe how fuzzy checkpointing is used in ARIES.

Choose the correct answer for each of the following multiple-choice questions:Incremental logging with deferred updates implies that the recovery system must necessarily a. store the old value of the updated item in the log. b. store the new value of the updated item in the log. c. store both the old and new value of the updated item in the log. d. store only the Begin Transaction and Commit Transaction records in the log.

(Review from Chapter 17 ) What is the system log used for? What are the typical kinds of entries in a system log? What are checkpoints, and why are they important? What are transaction commit points, and why are they important?

Choose the correct answer for each of the following multiple-choice questions: For incremental logging with immediate updates, a log record for a transaction would contain: a. a transaction name, data item name, old value of item, new value of item. b. a transaction name, data item name, old value of item. c. a transaction name, data item name, new value of item. d. a transaction name and a data item name.

How are buffering and caching techniques used by the recovery subsystem?
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