Transactions and concurrency control

Question 31

Consider the table R with attributes A, B and C. The functional dependencies that hold on R are : A → B, C → AB. Which of the following statements is/are True ? I. The decomposition of R into R₁(C, A) and R₂(A, B) is lossless. II. The decomposition of R into R₁(A, B) and R₂(B, C) is lossy.

• Only I
• Only II
• Both I and II
• Neither I nor II

Question 32

Which of the following concurrency protocol ensures both conflict serializability and freedom from deadlock? (a)z - phase Locking (b)Time stamp - ordering

• Both (a) and (b)
• (a) only
• (b) only
• Neither (a) nor (b)

Question 33

Which of the following contains complete record of all activity that affected the contents of a database during a certain period of time?

• Transaction log
• Query language
• Report writer
• Data manipulation language

Question 34

Which of the following scenarios may lead to an irrecoverable error in a database system?

• A transaction writes a data item after it is read by an uncommitted transaction
• A transaction reads a data item after it is read by an uncommitted transaction
• A transaction reads a data item after it is written by a committed transaction
• A transaction reads a data item after it is written by an uncommitted transaction

Question 35

Which of the following is correct with respect to Two phase commit protocol?

• Ensures serializability
• Prevents Deadlock
• Detects Deadlock
• Recover from Deadlock

Question 36

Which of the following is correct ? I.Two phase locking is an optimistic protocol. II. Two phase locking is pessimistic protocol III. Time stamping is an optimistic protocol. IV. Time stamping is pessimistic protocol.

• I and III
• II and IV
• I and IV
• II and III

Question 37

Let us assume that transaction T1 has arrived before transaction T2. Consider the schedule

S=r1(A); r2(B) ; w2(A); w1(B) 

Which of the following is true?

• Allowed under basic timestamp protocol.
• Not allowed under basic timestamp protocols because T1 is rolled back
• Not allowed under basic timestamp protocols because T2 is rolled back
• None of these

Question 38

Consider the following schedules involving two transactions. S₁: r₁ (X) ; r ₁ (Y) ; r ₂ (X) ; r ₂ (Y) ; w ₂ (Y) ; w₁ (X) S₂: r₁ (X) ; r ₂ (X) ; r ₂ (Y) ; w ₂ (Y) ; r ₁ (Y) ; w₁ (X) Which one of the following statements is correct with respect to above ?

• Both S₁ and S ₂ is conflict serializable.
• Both S₁ and S₂are not conflict serializable.
• S₁ is conflict serializable and S ₂ is not conflict serializable.
• S ₁is not conflict serializable and S ₂ is conflict serializable.

Question 39

Consider the relation R(P,Q,S,T,X,Y,Z,W) with the following functional dependencies. Consider the decomposition of the relation R into the constituent relations according to the following two decomposition schemes. Which one of the following options is correct?

• D1 is a lossless decomposition, but D2 is a lossy decomposition
• D1 is a lossy decomposition, but D2 is a lossless decomposition
• Both D1 and D2 are lossless decompositions
• Both D1 and D2 are lossy decompositions

Question 40

Let S be the following schedule of operations of three transactions T1, T2 and T3 in a relational database system:

R2(Y),R1(X),R3(Z),R1(Y)W1(X),R2(Z),W2(Y),R3(X),W3(Z) 

Consider the statements P and Q below:

• P: S is conflict-serializable.
• Q: If T3 commits before T1 finishes, then S is recoverable.

Which one of the following choices is correct?

• Both P and Q are true
• P is true and Q is false
• P is false and Q is true
• Both P and Q are false