Test series

Question

Consider the following schedules:

S1: w2(a) w1(a) w3(c) r1(a) r3(b) w2(b) r3(c)

S2: r3(a) r1(b) r3(a) w2(b) r1(a) r2(a) w2(c) r3(c)

What is the minimum value of the number of swaps required so that schedule S₂ has conflict serializability as in the same order as that of S₁?

Comments

Yes , direct swapping can solve the problem as just no. of swaps are required...either do it through position change or direct swaps.

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Why can't we just swap R1(b) with R3(c)? They are anyway a non-conflicting pair! By just one swap, we can achieve the order required of T3 -> T2 -> T1.

Pls correct me if I'm missing something here.

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Because your swaps would change the discrete nature of individual transaction , although it's not affecting serializability , but T3 is reading R(A) first you should not change the order of transaction., In transactions permuting the order of read write instructions is not be allowed ,

Let T1 be a transaction reading some value from bank on account A , T1 was instructed to read account A first , you can not make it read account C first , as transaction is nothing but a piece of code wriiten for sequential run , just as a program , so it will follow the hierarchy inside the lines of code .

Here it creates ambiguity as , it's not affecting final answer , as your swaps would change order sequence of T1  and T3