Managing Multiuser Databases Questions and Answers

Q: In this instance, dirty reads are disallowed, while nonrepeatable reads and phantom reads are allowed.

Correct answer: Read committedRead committed guarantees only that data read has been committed by someone, so dirty reads are impossible. It takes no long-term read locks, so a row may change between two reads within the same transaction - a non-repeatable read - and new rows may appear, a phantom. It is the default level in most systems, as a compromise between correctness and concurrency.

Q: A transaction is a series of actions to be taken on the database so that either all of them are performed successfully or none of them are performed at all.

Correct answer: TrueThis is the definition of a transaction and it is the atomicity property stated in full. The series of actions is treated as a single indivisible unit, so a transfer between two accounts either debits one and credits the other or does neither - the database is never left with the money in neither place.

Q: The overall responsibility of the DBA is to facilitate the development and use of the database.

Correct answer: TrueThe DBA’s role is to facilitate the development and use of the database rather than to own the data or to write the applications. In practice that covers design support, security administration, backup and recovery, performance, configuration control and the arbitration of conflicting requirements between user groups.

Q: Which of the following locks the item from change but not from read?

Correct answer: Shared lockA shared lock permits other transactions to read the item but not to change it, so any number of readers may hold one at once. An exclusive lock permits neither reading nor writing by anyone else. The pair is what allows concurrent reads to proceed freely while any write is serialised.

51.

In this instance, dirty reads are disallowed, while nonrepeatable reads and phantom reads are allowed.

A.Read committed
B.Read uncommitted
C.Repeatable read
D.Serializable

Answer: A

Correct answer: Read committed

Read committed guarantees only that data read has been committed by someone, so dirty reads are impossible. It takes no long-term read locks, so a row may change between two reads within the same transaction - a non-repeatable read - and new rows may appear, a phantom. It is the default level in most systems, as a compromise between correctness and concurrency.

Discuss in Forum

52.

A transaction is a series of actions to be taken on the database so that either all of them are performed successfully or none of them are performed at all.

A.True
B.False

Answer: A

Correct answer: True

This is the definition of a transaction and it is the atomicity property stated in full. The series of actions is treated as a single indivisible unit, so a transfer between two accounts either debits one and credits the other or does neither - the database is never left with the money in neither place.

Discuss in Forum

53.

The overall responsibility of the DBA is to facilitate the development and use of the database.

A.True
B.False

Answer: A

Correct answer: True

The DBA’s role is to facilitate the development and use of the database rather than to own the data or to write the applications. In practice that covers design support, security administration, backup and recovery, performance, configuration control and the arbitration of conflicting requirements between user groups.

Discuss in Forum

54.

Which of the following locks the item from change but not from read?

A.Implicit lock
B.Explicit lock
C.Exclusive lock
D.Shared lock

Answer: D

Correct answer: Shared lock

A shared lock permits other transactions to read the item but not to change it, so any number of readers may hold one at once. An exclusive lock permits neither reading nor writing by anyone else. The pair is what allows concurrent reads to proceed freely while any write is serialised.

Discuss in Forum

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Managing Multiuser Databases Questions and Answers

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