Data Recovery Techniques in Chapter 16

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What happens to a transaction when it enters the failed state in a database system?

It is rolled back and enters the aborted state. (correct)

It proceeds with normal execution.

It is immediately restarted as a new transaction.

It remains in the failed state indefinitely.

Under what circumstances can a failed transaction be restarted in a database system?

If the failure was due to a hardware or software error not created through the internal logic of the transaction. (correct)

If the failure was due to bad input data.

If the failure was due to not finding desired data in the database.

If the failure was due to an external logical error.

Why might a database system decide to kill a transaction?

Due to errors in hardware causing the failure.

Due to network issues preventing data retrieval from the database.

Due to bad input data received during the transaction.

Due to internal logical errors that require rewriting the application program. (correct)

Why is it essential to be cautious when dealing with observable external writes in a database system?

Because such writes cannot be erased once they have occurred. Signup and view all the answers

What does it mean for a transaction to be considered a new transaction when restarted in a database system?

It starts its execution from scratch with new attributes and operations. Signup and view all the answers

Why do most systems allow observable external writes only after a transaction has entered the committed state?

To avoid exposing partial or inconsistent data to users or external systems. Signup and view all the answers

What property in databases ensures that transactions either fully complete or have no effect at all?

Atomicity Signup and view all the answers

Which property refers to the requirement that transactions must operate independently without interference from other concurrently executing database statements?

Isolation Signup and view all the answers

What property ensures that transactions persist across system crashes in databases?

Durability Signup and view all the answers

In database systems, which property is violated if a system 'forgets' about a transaction after a crash?

Durability Signup and view all the answers

What is the term used to describe the 'all-or-none' property in databases which guarantees that transactions are indivisible?

Atomicity Signup and view all the answers

Which database property ensures that transactions execute without interference from other concurrent operations?

Isolation Signup and view all the answers

What happens if the system fails after a transaction has entered the committed state but before completing external writes?

The database system will carry out the external writes when the system is restarted. Signup and view all the answers

What is a possible issue when handling external writes for dispensing cash at an automated teller machine?

Dispensing cash when the user is present. Signup and view all the answers

What action needs to be taken if the database system crashes just after a booking transaction commits over the Web?

Executing a compensating transaction upon system restart. Signup and view all the answers

How is atomicity in databases related to handling system failures?

Atomicity guarantees that either all operations of a transaction are carried out or none are. Signup and view all the answers

Why is it important for applications to be designed such that users can verify the success of their transactions after a system failure?

To ensure users know whether they have to redo their transactions. Signup and view all the answers

In the context of database recovery systems, what does durability refer to?

Ensuring that all committed transactions persist through failures. Signup and view all the answers

Data Recovery Techniques in Chapter 16

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Questions and Answers

What happens to a transaction when it enters the failed state in a database system?

Under what circumstances can a failed transaction be restarted in a database system?

Why might a database system decide to kill a transaction?

Why is it essential to be cautious when dealing with observable external writes in a database system?

What does it mean for a transaction to be considered a new transaction when restarted in a database system?

Why do most systems allow observable external writes only after a transaction has entered the committed state?

What property in databases ensures that transactions either fully complete or have no effect at all?

Which property refers to the requirement that transactions must operate independently without interference from other concurrently executing database statements?

What property ensures that transactions persist across system crashes in databases?

In database systems, which property is violated if a system 'forgets' about a transaction after a crash?

What is the term used to describe the 'all-or-none' property in databases which guarantees that transactions are indivisible?

Which database property ensures that transactions execute without interference from other concurrent operations?

What happens if the system fails after a transaction has entered the committed state but before completing external writes?

What is a possible issue when handling external writes for dispensing cash at an automated teller machine?

What action needs to be taken if the database system crashes just after a booking transaction commits over the Web?

How is atomicity in databases related to handling system failures?

Why is it important for applications to be designed such that users can verify the success of their transactions after a system failure?

In the context of database recovery systems, what does durability refer to?

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