UGC NET CSE | October 2022 | Part 1 | Question: 10

Question

Consider the following statements:
Statement $\text{I}$: Conservative $2 \mathrm{PL}$ is a deadlock-free protocol.
Statement $\text{II}$: Thomas's write rule enforces conflict serializability.
Statement $\text{III}$: Timestamp ordering protocol ensures serializability based on the order of transaction timestamps.

Which of the following is correct?

• A. Statement $\text{I}$, Statement $\text{II}$ true and Statement $\text{III}$ false
• B. Statement $\text{I}$, Statement $\text{III}$ true and Statement $\text{II}$ false
• C. Statement $\text{I}$, Statement $\text{II}$ false and Statement $\text{III}$ true
• D. Statement $\text{I}$, Statement $\text{II}$ and Statement $\text{III}$ true

Answer 1

• Statement I: Conservative 2 PL is a protocol for managing concurrent access to a database and it aims to prevent deadlocks. Hence, Statement I is true. 

• Statement II: Thomas's write rule is a method for ensuring conflict serializability in database systems. It defines the conditions under which two transactions can write to the same data item and ensures that the transactions are executed in a serializable order. Hence, Statement II is true. 

• Statement III: Timestamp ordering protocol is a method for ensuring serializability in database systems by assigning a unique timestamp to each transaction. Transactions are executed in the order of their timestamps, which ensures that all conflicting transactions are executed in a serializable order. 

• Hence, Statement III is true.

Comments

Statement II is false as Thomas write rule ensures view serializability.