The GATE Grind

GATE 2019 CS – Question 21

Databases · Transactions and Concurrency Control · 1 mark · Multiple choice

Consider the following two statements about database transaction schedules:

I. Strict two-phase locking protocol generates conflict serializable schedules that are also recoverable.

II. Timestamp-ordering concurrency control protocol with Thomas' Write Rule can generate view serializable schedules that are not conflict serializable.

Which of the above statements is/are TRUE?

  1. I only
  2. II only
  3. Both I and II
  4. Neither I nor II

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Correct answer: (C) Both I and II

Explanation

Strict 2PL produces conflict serializable and strict (hence recoverable) schedules, so I is true. Thomas' Write Rule ignores obsolete writes, which can give schedules that are view serializable but not conflict serializable, so II is true.