Managing Multiuser Databases Questions and Answers

Q: A Transaction Manager is which of the following ?

A transaction manager does all three, so the answer is All of the above.It keeps a log of transactions for recovery (A), keeps before and after images of the database so that a transaction can be undone or redone (B), and applies concurrency control so that transactions running together do not interfere (C). Since each of those is one of its duties, any single option understates its role.

Q: Locks placed by command are implicit locks.

Correct answer: FalseLocks placed by command are explicit; implicit locks are those the DBMS places on its own initiative to enforce the isolation level in force. The two terms classify locks by who asked for them, which is a different question from whether the lock is shared or exclusive.

Q: The size of a lock is referred to as lock sizing.

Correct answer: FalseThe term is lock granularity, not lock sizing. It describes whether the lock covers a row, a page, a table or the whole database, and the choice trades concurrency against the overhead of tracking a large number of locks.

Q: A cursor type in which the application sees the data as they were at the time the cursor was opened is called:

Correct answer: static.A static cursor takes a snapshot of the data when it is opened and shows that snapshot throughout, so changes made by others afterwards are invisible. It is the opposite of the dynamic cursor, and the keyset cursor sits between them, showing changes to the rows originally selected but not rows added later.

Q: Locks placed by command are called ________ .

Correct answer: explicit locksAn explicit lock is one the application asks for by issuing a command; an implicit lock is one the DBMS places on its own initiative to enforce isolation. The distinction is about who requests the lock. Shared and exclusive describe something different - what the lock permits others to do - so the two classifications are independent.

Q: Locks placed by the DBMS are called ________ .

Correct answer: implicit locksLocks placed by the DBMS on its own initiative, to enforce the isolation level in force, are implicit. An explicit lock is one the application requests by command. Most locking in practice is implicit, which is the point of declaring an isolation level: the developer states what must be prevented and leaves the DBMS to arrange it.

Q: Money is defined in Oracle with the Currency data type.

Correct answer: FalseOracle has no Currency datatype. Money is held in a NUMBER column with an explicit precision and scale, such as NUMBER(9,2), which stores the value exactly rather than in binary floating point - and exactness is what matters for money. The Currency type belongs to other products.

Q: An ACID transaction is one that is atomic, consistent isolated, and durable.

Correct answer: TrueThe four properties are atomic, consistent, isolated and durable. Atomic means all or nothing; consistent means the database moves from one valid state to another; isolated means concurrent transactions do not see each other’s intermediate states; and durable means committed changes survive failure.

21.

A Transaction Manager is which of the following ?

A.Maintains a log of transactions
B.Maintains before and after database images
C.Maintains appropriate concurrency control
D.All of the above

Exam Year(s)

UGC NET - 2012,

Answer: D

A transaction manager does all three, so the answer is All of the above.

It keeps a log of transactions for recovery (A), keeps before and after images of the database so that a transaction can be undone or redone (B), and applies concurrency control so that transactions running together do not interfere (C). Since each of those is one of its duties, any single option understates its role.

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22.

What is Granularity ?

A.The size of database
B.The size of data item
C.The size of record
D.The size of file

Exam Year(s)

UGC NET - 2012,

Answer: B

Granularity, in database concurrency control, is the size of the data item that is locked or otherwise controlled as a unit, which can be a field value, a record, a disk block, a file or a whole database. Fine granularity means small items and permits more concurrent transactions, while coarse granularity means large items and less locking overhead. The sizes of the database, the record or the file are only some of the possible granules, so the general answer is the size of the data item, option (B).

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23.

The problem that occurs when one transaction updates a database item and then the transaction fails for some reason is ________.

A.Temporary Select Problem
B.Temporary Modify Problem
C.Dirty Read Problem
D.None

Exam Year(s)

UGC NET - 2012,

Answer: C

The problem in which one transaction updates a database item and then fails, so that the update is rolled back, while another transaction has already read the changed value, is the dirty read problem; some textbooks also call it the temporary update problem. The second transaction has then used a value that never existed in a committed state. Temporary select and temporary modify problems are not standard names for it. The answer is Dirty Read Problem, option (C).

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24.

Locks placed by command are implicit locks.

A.True
B.False

Answer: B

Correct answer: False

Locks placed by command are explicit; implicit locks are those the DBMS places on its own initiative to enforce the isolation level in force. The two terms classify locks by who asked for them, which is a different question from whether the lock is shared or exclusive.

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25.

The size of a lock is referred to as lock sizing.

A.True
B.False

Answer: B

Correct answer: False

The term is lock granularity, not lock sizing. It describes whether the lock covers a row, a page, a table or the whole database, and the choice trades concurrency against the overhead of tracking a large number of locks.

Discuss in Forum

26.

A cursor type in which the application sees the data as they were at the time the cursor was opened is called:

A.forward only.
B.static.
C.keyset.
D.dynamic.

Answer: B

Correct answer: static.

A static cursor takes a snapshot of the data when it is opened and shows that snapshot throughout, so changes made by others afterwards are invisible. It is the opposite of the dynamic cursor, and the keyset cursor sits between them, showing changes to the rows originally selected but not rows added later.

Discuss in Forum

27.

Locks placed by command are called ________ .

A.implicit locks
B.explicit locks
C.exclusive locks
D.shared locks

Answer: B

Correct answer: explicit locks

An explicit lock is one the application asks for by issuing a command; an implicit lock is one the DBMS places on its own initiative to enforce isolation. The distinction is about who requests the lock. Shared and exclusive describe something different - what the lock permits others to do - so the two classifications are independent.

Discuss in Forum

28.

Locks placed by the DBMS are called ________ .

A.implicit locks
B.explicit locks
C.exclusive locks
D.shared locks

Answer: A

Correct answer: implicit locks

Locks placed by the DBMS on its own initiative, to enforce the isolation level in force, are implicit. An explicit lock is one the application requests by command. Most locking in practice is implicit, which is the point of declaring an isolation level: the developer states what must be prevented and leaves the DBMS to arrange it.

Discuss in Forum

29.

Money is defined in Oracle with the Currency data type.

A.True
B.False

Answer: B

Correct answer: False

Oracle has no Currency datatype. Money is held in a NUMBER column with an explicit precision and scale, such as NUMBER(9,2), which stores the value exactly rather than in binary floating point - and exactness is what matters for money. The Currency type belongs to other products.

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30.

An ACID transaction is one that is atomic, consistent isolated, and durable.

A.True
B.False

Answer: A

Correct answer: True

The four properties are atomic, consistent, isolated and durable. Atomic means all or nothing; consistent means the database moves from one valid state to another; isolated means concurrent transactions do not see each other’s intermediate states; and durable means committed changes survive failure.

Discuss in Forum

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