MadeEasy Subject Test: Databases - Transactions

Question

Consider the following schedule :

S::r1(A),r3(D),w1(B),r2(B),r4(B),w2(C),r5(C),w4(E),r5(E),w5(B)

The number of serial schedules which are view equal to schedule (S) ___________.

Answer 1

Transactions T1 and T3 are performing initial reads on items A and D respectively. Since they have no R/W conflict among them, they can be ordered in 2 ways.

Transactions T2,T4  and T5 are performing final write on items C, E and B respectively in the said order.

T2 and  T4 do not have a R/W conflict among them. So they can be ordered in 2 ways.

Therefore, total orderings = 2*2*1 = 4.

Comments

initial read are performed on A and D which are not going to change in the schedule so why to fix them at the intial stage.?