This set of DBMS Transaction Scheduling MCQ Questions covers advanced concepts of Database Management Systems related to Conflict Serializability, View Serializability, Recoverability, Timestamp Ordering, Two-Phase Locking (2PL), Deadlock Prevention, and Transaction Scheduling. Useful for GATE, IBPS IT Officer, university semester examinations, technical interviews, and competitive exams.
Topic: DBMS – Concurrency Control | Set: 3
Difficulty: Hard | Total Questions: 15
DBMS Transaction Scheduling MCQ Question
Q1. Consider schedule S: R₁(X), W₂(X), W₁(X), C₁, C₂. This schedule is:
- A. Conflict Serializable
- B. Not Conflict Serializable
- C. Recoverable
- D. Strict
View Answer & Explanation
Answer: B
Explanation: The precedence graph contains T₁ → T₂ and T₂ → T₁, creating a cycle. Therefore, the schedule is not conflict serializable.
Q2. Schedule S: W₁(X), W₂(X), W₃(X), W₁(Y), C₁, C₂, C₃. Is this schedule Recoverable?
- A. Yes, because there are no Read-After-Write dependencies
- B. No, because T₁ writes X before T₂
- C. No, because T₃ is the last to write X
- D. Only if T₁ aborts
View Answer & Explanation
Answer: A
Explanation: Recoverability focuses on Read-After-Write dependencies. Since no transaction reads another transaction’s uncommitted data, the schedule is recoverable.
Q3. Which statement about the relationship between schedule classes is TRUE?
- A. Strict ⊂ Cascadeless ⊂ Recoverable
- B. Recoverable ⊂ Cascadeless ⊂ Strict
- C. Conflict Serializable ⊂ Recoverable
- D. View Serializable ⊂ Conflict Serializable
View Answer & Explanation
Answer: A
Explanation: Strict schedules are a subset of Cascadeless schedules, which are themselves a subset of Recoverable schedules.
Q4. If a schedule S has a cycle in its precedence graph, it could still be View Serializable if:
- A. It contains no Write operations
- B. It contains Blind Writes
- C. It is a serial schedule
- D. It is irrecoverable
View Answer & Explanation
Answer: B
Explanation: Blind writes can allow view equivalence even when conflict equivalence is impossible due to cyclic dependencies.
Q5. In Timestamp Ordering, if Tᵢ attempts to R(X) but TS(Tᵢ) < W-timestamp(X):
- A. Tᵢ is allowed to read
- B. Tᵢ is rolled back
- C. Tᵢ waits for the writer to commit
- D. The writer is rolled back
View Answer & Explanation
Answer: B
Explanation: The transaction is too old compared to the last write timestamp and must be rolled back to maintain timestamp ordering.
Q6. A schedule S is R₁(X), W₁(X), R₂(X), W₂(Y), C₂, C₁. This schedule is:
- A. Recoverable
- B. Irrecoverable
- C. Cascadeless
- D. Strict
View Answer & Explanation
Answer: B
Explanation: T₂ reads uncommitted data written by T₁ and commits before T₁ commits, making the schedule irrecoverable.
Q7. Which concurrency control protocol guarantees both Serializability and freedom from Deadlocks?
- A. Two-Phase Locking (2PL)
- B. Strict 2PL
- C. Timestamp Ordering
- D. Precedence Graph
View Answer & Explanation
Answer: C
Explanation: Timestamp Ordering avoids deadlocks by enforcing a global ordering of transaction timestamps.
Q8. A schedule S has n transactions. How many possible serial schedules exist?
- A. n
- B. n²
- C. n!
- D. 2ⁿ
View Answer & Explanation
Answer: C
Explanation: Any permutation of n transactions represents a valid serial schedule, resulting in n! possibilities.
Q9. In the context of View Serializability, the “Final Write” condition ensures:
- A. The last transaction to write an item in S is the same as in S’
- B. Every transaction commits
- C. No blind writes exist
- D. The precedence graph is acyclic
View Answer & Explanation
Answer: A
Explanation: The final write condition guarantees that the database state after concurrent execution matches the equivalent serial execution.
Q10. The “Wait-Die” and “Wound-Wait” schemes are used to:
- A. Ensure Recoverability
- B. Prevent Deadlocks in locking protocols
- C. Check for View Serializability
- D. Eliminate Internal Fragmentation
View Answer & Explanation
Answer: B
Explanation: These schemes use timestamps to determine whether transactions should wait or abort, preventing deadlocks.
Q11. Consider S: W₁(X), W₂(X), W₁(X). Is this conflict serializable?
- A. Yes, equivalent to T₁, T₂
- B. Yes, equivalent to T₂, T₁
- C. No, it has a cycle
- D. Only if X = 0
View Answer & Explanation
Answer: C
Explanation: The schedule creates both T₁ → T₂ and T₂ → T₁ dependencies, resulting in a cyclic precedence graph.
Q12. Rigorous Two-Phase Locking (Rigorous 2PL) is:
- A. Not serializable
- B. Always Strict
- C. Only for read-only databases
- D. Prone to cascading rollbacks
View Answer & Explanation
Answer: B
Explanation: Rigorous 2PL holds all locks until commit or abort, ensuring strict and serializable schedules.
Q13. If a schedule is “View Serializable” but NOT “Conflict Serializable,” it MUST have:
- A. At least one Dirty Read
- B. At least one Blind Write
- C. At least one Deadlock
- D. At least three transactions
View Answer & Explanation
Answer: B
Explanation: Blind writes are necessary for a schedule to be view serializable while not being conflict serializable.
Q14. A system using the “Wait-Die” scheme: T₁ (TS = 10) requests a lock held by T₂ (TS = 20). What happens?
- A. T₁ dies
- B. T₁ waits
- C. T₂ dies
- D. T₂ waits
View Answer & Explanation
Answer: B
Explanation: In Wait-Die, an older transaction is allowed to wait, while a younger transaction must abort.
Q15. Which of the following results in a “Phantom Problem”?
- A. A transaction reads a value that is deleted by another
- B. A transaction’s range query result changes because another transaction inserted new rows
- C. A transaction writes a value that is never read
- D. A transaction fails after committing
View Answer & Explanation
Answer: B
Explanation: Phantom problems occur when rows satisfying a query condition appear or disappear due to concurrent insert or delete operations.
Conclusion
These advanced DBMS Concurrency Control MCQ Questions help strengthen concepts related to Serializability, Recoverability, Timestamp Ordering, Deadlock Prevention, Two-Phase Locking, and Transaction Scheduling. These topics are frequently asked in GATE, IBPS IT Officer, university semester examinations, and technical interviews.
For better understanding, also practice concepts related to Normalization, Transaction Management, Indexing, and Database Recovery Techniques.
For detailed theory and understanding of concepts, refer to DBMS Scheduling in Transactions.