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: Which concurrency control protocol uses timestamp ordering ?

The protocol is the timestamp-based protocol.The timestamp-ordering protocol gives each transaction a unique timestamp when it starts and keeps a read and a write timestamp on each data item. A conflicting operation that would break timestamp order is rejected and its transaction rolled back, so the schedule is equivalent to running transactions in timestamp order.Two-phase locking orders transactions by locks, not timestamps. Validation-based (optimistic) control does use timestamps, but to check at commit time rather than to order operations. Snapshot isolation reads from a consistent snapshot. Neither is the timestamp-ordering protocol.

Q: What does ACID stand for in database transactions ?

ACID stands for Atomicity, Consistency, Isolation, Durability.Atomicity means a transaction happens completely or not at all. Consistency means it takes the database from one valid state to another. Isolation means concurrent transactions do not see each other's partial work. Durability means committed changes survive crashes. Together these properties make transactions reliable.The other expansions swap in accuracy, concurrency, integrity or distribution. These are related database ideas, but they are not the four ACID properties.

Q: Which of the following scenarios may lead to an irrecoverable error in a database system ?

The scenario is a transaction reads a data item after it is written by an uncommitted transaction.This is a dirty read. If the reading transaction commits and the writing transaction then aborts, the reader has committed a decision based on a value that never officially existed, and it cannot be rolled back. The schedule is not recoverable.Reading after another read causes no conflict. Reading a value written by a committed transaction is safe. Writing after an uncommitted read is a write-after-read conflict, which affects serializability but does not make committed work depend on an aborted value.

Q: Consider the following transaction involving two bank accounts x and y.read(x); x := x - 50; write(x); read(y); y := y + 50; write(y)The constraint that the sum of the accounts x and y should remain constant is that of

The constraint is that of Consistency.Consistency means a transaction takes the database from one valid state to another, preserving its integrity constraints. Keeping the sum of x and y unchanged after moving 50 from one account to the other is exactly such a constraint.Atomicity ensures both writes happen or neither does, isolation keeps concurrent transactions from seeing each other's intermediate states, and durability keeps committed results after a crash. None of them is the rule about the sum itself.

Q: In a high-concurrency database system, two transactions are waiting for each other's locked resources. What is the most effective automatic way for a DBMS to handle this situation ?

The most effective automatic method is Deadlock detection and victim selection.Two transactions each waiting for a lock the other holds is a deadlock. A DBMS detects it by finding a cycle in the wait-for graph, then chooses a victim, typically the transaction that has done the least work, and rolls it back so the other can proceed. The victim is restarted later.A larger buffer cache does nothing about lock waits. Switching to optimistic locking is a design change, not an automatic response to a deadlock in progress. Spooling avoids deadlock for devices such as printers, not database locks.

Q: Which database property ensures that even in the event of a system failure or power loss, the results of a committed transaction are permanently recorded ?

The property is Durability.Durability, the D of ACID, guarantees that once a transaction commits, its changes survive any later failure, including a crash or power loss. DBMSs achieve this by writing the transaction's log records to stable storage before the commit is acknowledged (write-ahead logging) and replaying them on recovery.Atomicity means a transaction happens completely or not at all, consistency means it moves the database between valid states, and isolation means concurrent transactions do not see each other's intermediate work.

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.

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.

Which concurrency control protocol uses timestamp ordering ?

A.Two-phase locking
B.Timestamp-based protocol
C.Validation-based protocol
D.Snapshot isolation

Exam Year(s)

Tripura Public Service Commission - 2026,

Answer: B

The protocol is the timestamp-based protocol.

The timestamp-ordering protocol gives each transaction a unique timestamp when it starts and keeps a read and a write timestamp on each data item. A conflicting operation that would break timestamp order is rejected and its transaction rolled back, so the schedule is equivalent to running transactions in timestamp order.

Two-phase locking orders transactions by locks, not timestamps. Validation-based (optimistic) control does use timestamps, but to check at commit time rather than to order operations. Snapshot isolation reads from a consistent snapshot. Neither is the timestamp-ordering protocol.

Discuss in Forum

15.

What does ACID stand for in database transactions ?

A.Atomicity, Consistency, Isolation, Durability
B.Accuracy, Consistency, Integrity, Durability
C.Atomicity, Concurrency, Isolation, Distribution
D.Accuracy, Concurrency, Integrity, Distribution

Exam Year(s)

Tripura Public Service Commission - 2026,

Answer: A

ACID stands for Atomicity, Consistency, Isolation, Durability.

Atomicity means a transaction happens completely or not at all. Consistency means it takes the database from one valid state to another. Isolation means concurrent transactions do not see each other's partial work. Durability means committed changes survive crashes. Together these properties make transactions reliable.

The other expansions swap in accuracy, concurrency, integrity or distribution. These are related database ideas, but they are not the four ACID properties.

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16.

Which of the following scenarios may lead to an irrecoverable error in a database system ?

A.A transaction writes a data item after it is read by an uncommitted transaction.
B.A transaction reads a data item after it is read by an uncommitted transaction.
C.A transaction reads a data item after it is written by a committed transaction.
D.A transaction reads a data item after it is written by an uncommitted transaction.

Exam Year(s)

Tripura Public Service Commission - 2025,

Answer: D

The scenario is a transaction reads a data item after it is written by an uncommitted transaction.

This is a dirty read. If the reading transaction commits and the writing transaction then aborts, the reader has committed a decision based on a value that never officially existed, and it cannot be rolled back. The schedule is not recoverable.

Reading after another read causes no conflict. Reading a value written by a committed transaction is safe. Writing after an uncommitted read is a write-after-read conflict, which affects serializability but does not make committed work depend on an aborted value.

Discuss in Forum

17.

Consider the following transaction involving two bank accounts x and y.

read(x); x := x - 50; write(x); read(y); y := y + 50; write(y)

The constraint that the sum of the accounts x and y should remain constant is that of

A.Atomicity
B.Consistency
C.Isolation
D.Durability

Exam Year(s)

Tripura Public Service Commission - 2025,

Answer: B

The constraint is that of Consistency.

Consistency means a transaction takes the database from one valid state to another, preserving its integrity constraints. Keeping the sum of x and y unchanged after moving 50 from one account to the other is exactly such a constraint.

Atomicity ensures both writes happen or neither does, isolation keeps concurrent transactions from seeing each other's intermediate states, and durability keeps committed results after a crash. None of them is the rule about the sum itself.

Discuss in Forum

18.

In a high-concurrency database system, two transactions are waiting for each other's locked resources. What is the most effective automatic way for a DBMS to handle this situation ?

A.Switching from pessimistic to optimistic locking
B.Increase the size of the database buffer cache
C.Deadlock detection and victim selection
D.Deadlock prevention using spooling

Exam Year(s)

Tripura Public Service Commission - 2026,

Answer: C

The most effective automatic method is Deadlock detection and victim selection.

Two transactions each waiting for a lock the other holds is a deadlock. A DBMS detects it by finding a cycle in the wait-for graph, then chooses a victim, typically the transaction that has done the least work, and rolls it back so the other can proceed. The victim is restarted later.

A larger buffer cache does nothing about lock waits. Switching to optimistic locking is a design change, not an automatic response to a deadlock in progress. Spooling avoids deadlock for devices such as printers, not database locks.

Discuss in Forum

19.

Which database property ensures that even in the event of a system failure or power loss, the results of a committed transaction are permanently recorded ?

A.Consistency
B.Isolation
C.Durability
D.Atomicity

Exam Year(s)

Tripura Public Service Commission - 2026,

Answer: C

The property is Durability.

Durability, the D of ACID, guarantees that once a transaction commits, its changes survive any later failure, including a crash or power loss. DBMSs achieve this by writing the transaction's log records to stable storage before the commit is acknowledged (write-ahead logging) and replaying them on recovery.

Atomicity means a transaction happens completely or not at all, consistency means it moves the database between valid states, and isolation means concurrent transactions do not see each other's intermediate work.

Discuss in Forum

20.

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

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