Consider the following schedule S of transactions T1, T2, T3, T4:

Consider the following four schedules due to three transactions (indicated by the subscript) using read and write on a data item x, denoted by r(x) and w(x) respectively. Which one of them is conflict serializable?

Consider the transactions T1, T2, and T3 and the schedules S1 and S2 given below.

T1 : r1 (X) ; r1 (Z) ; w1 (X) ; w1 (Z)

T2 : r2 (X) ; r2 (Z) ; w2 (Z)

T3 : r3 (X) ; r3 (X) ; w3 (Y)

S1: r1(X); r3(Y); r3(X); r2(Y); r2(Z); w3(Y); w2(Z); r1(Z); w1(X); w1(Z)

S2: r1(X); r3(Y); r2(Y); r3(X); r1(Z); r2(Z); w3(Y); w1(X); w2(Z); w1(Z)

Which one of the following statements about the schedules is TRUE?

Consider the following transactions with data items P and Q initialized to zero:

T1 : read (P) ; 
     read (Q) ; 
     if P = 0 then Q : = Q + 1 ; 
     write (Q). 

T2 : read (Q) ; 
     read (P) 
     if Q = 0 then P : = P + 1 ; 
     write (P).

Any non-serial interleaving of T₁ and T₂ for concurrent execution leads to