Managing Multiuser Databases Questions and Answers

Q: Which of the following are the lock modes in multiple granularity locking ?(i) S(ii) X(iii) SIX(iv) IX(v) IS

All five are lock modes, so the answer is (i), (ii), (iii), (iv) and (v).Multiple granularity locking adds intention modes to the ordinary shared (S) and exclusive (X) locks, so that a transaction can lock a whole file or a single record consistently. IS (intention-shared) and IX (intention-exclusive) on a node announce shared or exclusive locks lower in the tree, and SIX (shared and intention-exclusive) locks a node in shared mode while signalling exclusive locks below.Each of the narrower options leaves out one or more of these standard modes.

Q: Which amongst the following statements are correct ?(i) Writing a database object without reading its initial value is called Blind write(ii) In wound wait technique, the number of rollback is low(iii) In wait-die technique, the younger transaction is never rolled back(iv) The different locks in 2PL mechanism are shared, read, write and unlock.

Statements (i) and (ii) are correct, so the answer is (i) & (ii).(i) A blind write is exactly a write to a data item that the transaction has not read first. (ii) In wound-wait, an older transaction wounds (rolls back) a younger one, but a younger transaction simply waits for an older one; this is generally reckoned to cause fewer rollbacks than wait-die.(iii) is false: in wait-die it is precisely the younger transaction that dies (is rolled back) when it requests an item held by an older one. (iv) is false: two-phase locking uses shared (read) and exclusive (write) locks, with unlock as an operation, not a lock mode, and 'shared' and 'read' are the same lock. Any option including (iii) or (iv) is therefore wrong.

Q: A transaction enters into its partially committed state :

A transaction becomes partially committed when it finishes the execution of its final statement.The transaction states are active, partially committed, committed, failed and aborted. After the last statement executes, the transaction is partially committed: its effects may still be only in memory buffers. It becomes committed once enough information has been written to stable storage, which is when the commit record reaches the log.Starting the first statement puts a transaction in the active state, writing COMMIT to the log marks the committed state, and every successful transaction passes through partial commit.

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.

11.

Which of the following are the lock modes in multiple granularity locking ?

(i) S
(ii) X
(iii) SIX
(iv) IX
(v) IS

A.(i) and (ii)
B.(i), (ii) and (iii)
C.(i), (ii), (iv) and (v)
D.(i), (ii), (iii), (iv) and (v)

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: D

All five are lock modes, so the answer is (i), (ii), (iii), (iv) and (v).

Multiple granularity locking adds intention modes to the ordinary shared (S) and exclusive (X) locks, so that a transaction can lock a whole file or a single record consistently. IS (intention-shared) and IX (intention-exclusive) on a node announce shared or exclusive locks lower in the tree, and SIX (shared and intention-exclusive) locks a node in shared mode while signalling exclusive locks below.

Each of the narrower options leaves out one or more of these standard modes.

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12.

Which amongst the following statements are correct ?

(i) Writing a database object without reading its initial value is called Blind write
(ii) In wound wait technique, the number of rollback is low
(iii) In wait-die technique, the younger transaction is never rolled back
(iv) The different locks in 2PL mechanism are shared, read, write and unlock.

A.(i), (ii) and (iii)
B.(i) & (ii)
C.(i), (ii) and (iv)
D.(ii), (iii) and (iv)

Exam Year(s)

MH SET - 2023, SET Exam - 2023,

Answer: B

Statements (i) and (ii) are correct, so the answer is (i) & (ii).

(i) A blind write is exactly a write to a data item that the transaction has not read first. (ii) In wound-wait, an older transaction wounds (rolls back) a younger one, but a younger transaction simply waits for an older one; this is generally reckoned to cause fewer rollbacks than wait-die.

(iii) is false: in wait-die it is precisely the younger transaction that dies (is rolled back) when it requests an item held by an older one. (iv) is false: two-phase locking uses shared (read) and exclusive (write) locks, with unlock as an operation, not a lock mode, and 'shared' and 'read' are the same lock. Any option including (iii) or (iv) is therefore wrong.

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13.

A transaction enters into its partially committed state :

A.When it finishes the execution of final statement
B.When it starts the execution of first statement
C.After writing 'COMMIT' into log
D.It never enters partially committed state

Exam Year(s)

MH SET - 2024, SET Exam - 2024,

Answer: A

A transaction becomes partially committed when it finishes the execution of its final statement.

The transaction states are active, partially committed, committed, failed and aborted. After the last statement executes, the transaction is partially committed: its effects may still be only in memory buffers. It becomes committed once enough information has been written to stable storage, which is when the commit record reaches the log.

Starting the first statement puts a transaction in the active state, writing COMMIT to the log marks the committed state, and every successful transaction passes through partial commit.

Discuss in Forum

14.

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.

Discuss in Forum

15.

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

16.

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

17.

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

18.

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

19.

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.

Discuss in Forum

20.

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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