GATE CSE 2007 | Transactions and Concurrency Question 26 | Database Management System

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GATE CSE 2007

MCQ (Single Correct Answer)

-0.6

Consider the following schedules involving two transactions. Which one of the following statements is TRUE?

S₁: r₁(X); r₁(Y); r₂(Y); r₂(X); w₂(Y); w₁(X);

S₂: r₁(X); r₂(X); r₂(Y); w₂(Y); r₁(Y); w₁(X);

Both S₁ and S₂ are conflict serializable.

S₁ is conflict serializable and S₂ is not conflict serializable.

S₁ is not conflict serializable and S₂ is conflict serializable.

Both S₁ and S₂ are not conflict serializable.

GATE CSE 2007

MCQ (Single Correct Answer)

-0.6

Consider the following two transactions: T₁ and T₂.

T₁: read (A);                  T₂: read (B);
    read (B);                      read (A);
    if A = 0 then B ← B + 1;       if B ≠ 0 then A ← A - 1;
    write (B);                     write (A);

Which of the following schemes, using shared and exclusive locks, satisfy the requirements for strict two phase locking for the above transactions?

S1 : lockS(A); 	        S2 : lockS(B);
     read (A);               read (B);
     lockS(B);               lockS(A);
     read (B);               read (A);
     if A = 0                if B ≠ 0
     then B ← B + 1;        then A ← A - 1;
     write (B);              write (A);
     commit;                 commit;
     unlock (A);             unlock (B);
     unlock (B);             unlock (A);

S1 : lockX(A);          S2 : lockX(B);
     read (A);               read (B);
     lockX(B);               lockX(A);
     read (B);               read (A);
     if A = 0                if B ≠ 0
     then B ← B + 1;        then A ← A - 1;
     write (B);              write (A);
     unlock (A);             unlock (A);
     commit;                 commit;
     unlock (B);             unlock (A);

S1 : lockS(A);           S2 : lockS(B);
     read (A);                read (B);
     lockX(B);                lockX(A);
     read (B);                read (A);
     if A = 0                 if B ≠ 0
     then B ← B + 1;         then A ← A - 1;
     write (B);               write (A);
     unlock (A);              unlock (B);
     commit;                  commit;
     unlock (B);              unlock (A);

S1 : lockS(A);           S2 : lockS(B);
     read (A);                read (B);
     lockX(B);                lockX(A);
     read (B);                read (A);
     if A = 0                 if B ≠ 0
    then B ← B + 1;        then A ← A - 1;
     write (B);               write (A);                                                                                                     
     unlock (A);              unlock (A);
     unlock (B);              unlock (B);
     commit;                  commit;

GATE CSE 2004

MCQ (Single Correct Answer)

-0.6

Consider the following schedule S of transactions T1 and T2: GATE CSE 2004 Database Management System - Transactions and Concurrency Question 27 English

GATE CSE 2004 Database Management System - Transactions and Concurrency Question 27 English

Which of the following is TRUE about the schedule S?

S is serializable only as T1,T2

S is serializable only as T2,T1

S is serializable both as T1, T2 and T2, T2

S is not serializable either as T1 or as T2

GATE CSE 2003

MCQ (Single Correct Answer)

-0.6

Consider three data items D1, D2, and D3, and the following execution schedule of transactions T1, T2, and T3. In the diagram, R(D) and W(D) denote the actions reading and writing the data item D respectively. GATE CSE 2003 Database Management System - Transactions and Concurrency Question 28 English