Serializability Quiz

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Question 1

Thomas' Write Rule allows schedules that are View Serializable but may not be Conflict Serializable. Which of the following conditions inherent to Thomas' Write Rule makes this possible?

(GATE 2015 | MCQ | 1-Mark)

  • The use of shared and exclusive lock transitions during execution

  • The presence of un-executable blind writes that are safely ignored by the system

  • The implementation of a strict two-phase locking constraint on all read operations

  • The system forcing younger transactions to roll back whenever a write-write conflict occurs

Question 2

Consider three transactions [Tex]T_1, T_2,[/Tex] and [Tex]T_3 [/Tex]with timestamps[Tex] TS(T_1) = 200, TS(T_2) = 300, [/Tex]0, and [Tex]TS(T_3) = 400[/Tex]. The initial write timestamp of data item X is [Tex]W\_TS(X) = 100[/Tex]. The following operations occur sequentially in a schedule:

  1. [Tex]T_2 [/Tex]executes W(X)
  2. [Tex]T_1[/Tex] executes W(X)
  3. [Tex]T_3[/Tex] executes W(X)

If the DBMS employs Thomas' Write Rule, what will be the final value of [Tex]W\_TS(X) [/Tex]after all three operations are processed?

(GATE 2011 | MCQ | 1-Mark)

  • 200

  • 300

  • 400

  • The schedule will abort at step 2, leaving [Tex]W\_TS(X) = 300[/Tex]

Question 3

What is a precedence graph used for?

  • Scheduling disk access

  • Testing deadlock

  • Testing conflict serializability

  • Measuring transaction execution time

Question 4

In a precedence graph, what does a cycle indicate?

  • A schedule is serializable

  • The schedule is view equivalent

  • A deadlock has occurred

  • The schedule is not conflict-serializable

Question 5

Which of the following is not required for view equivalence between two schedules?

  • Same set of transactions

  • Same read-from relationship

  • Same final write

  • Same lock types

Question 6

Consider a database system running the Thomas' Write Rule concurrency control protocol. A transaction [Tex]T_i [/Tex]with timestamp [Tex]TS(T_i) [/Tex]attempts to perform a write operation W(X) on a data item X. Let [Tex]R\_TS(X)[/Tex] and[Tex] W\_TS(X)[/Tex] denote the read and write timestamps of $X$, respectively. Under which of the following conditions will the write operation W(X) be safely IGNORED without aborting transaction [Tex]T_i[/Tex] ?

(GATE 2017 | MCQ | 1-Mark)

  • [Tex]TS(T_i) < R\_TS(X)[/Tex]

  • [Tex]TS(T_i) > W\_TS(X)[/Tex]

  • [Tex]R\_TS(X) < TS(T_i) < W\_TS(X)[/Tex]

  • [Tex]TS(T_i) > R\_TS(X)[/Tex] and [Tex]TS(T_i) > W\_TS(X)[/Tex]

Question 7

Consider a simple checkpointing protocol and the following set of operations in the log.

(start, T4); (write, T4, y, 2, 3); (start, T1); (commit, T4); (write, T1, z, 5, 7);

(checkpoint);

(start, T2); (write, T2, x, 1, 9); (commit, T2); (start, T3), (write, T3, z, 7, 2);

If a crash happens now and the system tries to recover using both undo and redo operations, what are the contents of the undo list and the redo list?

(GATE 2015 | MCQ | 1-Mark)

  • It considers lock types

  • It checks transaction priorities

  • It ignores final writes

  • It is based on read-from and final-write relationships

Question 8

Which of the following always guarantees a conflict-serializable schedule?

  • Precedence graph without cycles

  • View-equivalent schedules

  • Timestamp ordering protocol

  • Deadlock detection

Question 9

Which is easier to test programmatically:

  • View serializability

  • Conflict serializability

  • Both equally

  • Neither

Question 10

Consider the following schedule for transactions T1, T2 and T3:

Which one of the schedules below is the correct serialization of the above?

(GATE 2010 | MCQ | 1-Mark)

  • T1 → T3 → T2

  • T2 → T1 → T3

  • T2  → T3 → T1

  • T3 → T1 →  T2

There are 10 questions to complete.

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