Chapter 19: Problem 9

What is meant by transaction rollback? What is meant by cascading rollback? Why do practical recovery methods use protocols that do not permit cascading rollback? Which recovery techniques do not require any rollback?

Short Answer

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A transaction rollback refers to when a transaction is reversed or cancelled due to a failure. A cascading rollback occurs when the rollback of one transaction leads to rollbacks in others. Cascading rollbacks are avoided in practical recovery methods due to their computational cost and the complexity involved. Recovery techniques like Immediate Update method do not require rollbacks, as changes are made prior to a transaction reaching its commit point, meaning if a crash occurs before this point, the changes will not be reflected, thus eliminating the need for a rollback.

Step by step solution

Defining Transaction Rollback

A transaction rollback is a process in database management where a transaction is canceled or reversed. If the system determines that a particular transaction cannot be carried out or completed successfully, the changes made during the transaction are 'rolled back' or returned to their original state before the transaction began.

Explaining Cascading Rollback

Cascading rollback is a process where the rollback of a single transaction can lead to a series of rollbacks for other transactions. This mostly happens when different transactions are interdependent; a failure in one causes the failure of the others.

Why Avoid Cascading Rollback

Practical recovery methods use protocols that do not permit cascading rollbacks to avoid the expensive computational cost and system complexities involved. Cascading rollback requires maintaining logs for transactions and their states, making recovery process very complex, time-consuming, and resource-consuming. It also increases the chance of data inconsistency and database system instability.

Rollback-Free Recovery Techniques

As to recovery techniques that do not require any rollback, the Immediate Update method is an example. In immediate update, changes are made to the disk before a transaction reaches its commit point. If a crash occurs before the transaction reaches its commit point, then the changes will not be reflected, which means there is no need for a rollback. However, this method requires careful handling and management to ensure data consistency.

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What is meant by transaction rollback? What is meant by cascading rollback? Why do practical recovery methods use protocols that do not permit cascading rollback? Which recovery techniques do not require any rollback?

Short Answer

Step by step solution

Defining Transaction Rollback

Explaining Cascading Rollback

Why Avoid Cascading Rollback

Rollback-Free Recovery Techniques

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