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 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

Consider the following schedule for transactions T1, T2 and T3: Which one of the schedules below is the correct serialization of the above?