This set of Multiple Choice Questions (MCQs) covers advanced concepts of DBMS Transaction Scheduling including serializability, recoverability, strict schedules, and anomalies like dirty reads and lost updates. Useful for GATE and IBPS IT Officer exams.
Topic: Database Management System (Transaction Scheduling) | Set: 2
Difficulty: Medium to Hard | Total Questions: 15
DBMS Transaction Scheduling MCQs
Q1. A schedule S involves T₁ writing X and then T₂ reading X. If T₂ commits and then T₁ aborts, the schedule is:
A. Recoverable
B. Irrecoverable
C. Cascadeless
D. Strict
View Answer & Explanation
Answer: B
Explanation: T₂ committed based on uncommitted (dirty) data from T₁.
Q2. If a precedence graph contains T₁ → T₂ and T₂ → T₁, then the schedule is:
A. Conflict Serializable
B. Not Conflict Serializable
C. View Serializable
D. Recoverable
View Answer & Explanation
Answer: B
Explanation: A cycle means no equivalent serial schedule exists.
Q3. Which schedule avoids cascading rollbacks?
A. Recoverable
B. Cascadeless
C. Non-serial
D. Irrecoverable
View Answer & Explanation
Answer: B
Explanation: Transactions only read committed data.
Q4. A strict schedule ensures:
A. Immediate reads
B. Read/write after commit
C. No concurrency
D. Linear graph
View Answer & Explanation
Answer: B
Explanation: Prevents dirty reads and dirty writes.
Q5. View serializability is:
A. Easy to check
B. NP-Complete
C. Graph-based
D. Serial only
View Answer & Explanation
Answer: B
Explanation: It is computationally expensive to determine.
Q6. If no blind writes exist, view serializable ⇒
A. Conflict Serializable
B. Strict
C. Recoverable
D. Irrecoverable
View Answer & Explanation
Answer: A
Explanation: Without blind writes, both become equivalent.
Q7. T₁: W(A), T₂: W(A) is:
A. RW Conflict
B. WW Conflict
C. RR Conflict
D. No Conflict
View Answer & Explanation
Answer: B
Explanation: Two writes on same data item conflict.
Q8. Conflict equivalence means:
A. Same transactions
B. Same conflict order
C. Same output
D. Cycles existView Answer & Explanation
View Answer & Explanation
Answer: B
Explanation: Order of conflicting operations must match.
Q9. In a recoverable schedule, if T₁ fails before T₂ commits:
A. T₂ aborts
B. T₂ commits
C. Crash
D. Auto commit
View Answer & Explanation
Answer: A
Explanation: Cascading rollback occurs.
Q10. Strict schedule requires:
A. Only read condition
B. Only write condition
C. Both read & write conditions
D. None
View Answer & Explanation
Answer: C
Explanation: Must wait for commit before read/write.
Q11. Lost update violates:
A. Atomicity
B. Isolation
C. Durability
D. None
View Answer & Explanation
Answer: B
Explanation: Concurrent updates overwrite each other.
Q12. Conflict serializable schedule is equivalent to:
A. One serial schedule
B. At least one serial schedule
C. Zero
D. Two
View Answer & Explanation
Answer: B
Explanation: Must match at least one serial order.
Q13. Which does NOT ensure serializability?
A. 2PL
B. Timestamp
C. MVCC
D. More users
View Answer & Explanation
Answer: D
Explanation: More users increase concurrency, not correctness.
Q14. View serializable means:
A. Recoverable
B. Equivalent to serial
C. Conflict serializable
D. Cascadeless
View Answer & Explanation
Answer: B
Explanation: Must match a serial execution view.
Q15. Dirty write occurs when:
A. Read uncommitted
B. Overwrite uncommitted data
C. Disk failure
D. Parallel read
View Answer & Explanation
Answer: B
Explanation: Overwriting uncommitted data causes inconsistency.
Conclusion
These DBMS Transaction Scheduling MCQs help strengthen your understanding of key concepts like serializability, recoverability, strict schedules, and common anomalies such as dirty reads and lost updates. These topics are crucial for competitive exams like GATE, IBPS IT Officer, and technical interviews.
Practicing these questions regularly will improve your ability to analyze transaction schedules and understand how databases maintain consistency in concurrent environments.
For detailed theory and understanding of concepts, refer to DBMS Scheduling in Transactions.