Applied Test Series: Mock

Question

Consider the following schedule S:

S: R3(A), W2(A), R1(A), W3(A), W1(A);

The possible number of view serializable schedules of the schedule S (other than S) are _____

Can someone help me in this.

Answer 1

For having two schedules as view equivalent (hence view serializable),  we have to check for three conditions to be true in both schedules :

1.Initial Read

2.Write – Read pair

3.Final Write 

Here in this question as T3 reads A first so in every view equivalent schedule R3(A) remains same . Similarly T1 makes final write on A  so W1(A) remains same.

Now considering W-R pair since T1 reads value of  A written by T2,hence every view equivalent schedule must have same order .Here we can swap W3(A) and W2(A) means we can perform W3(A) before W2(A) and R1(A).

So one more possible view serializable schedule of the schedule S is R3(A), W3(A), W2(A), R1(A), W1(A);

Answer is one 

 

Answer 2

Is one is answere

Comments

Yes Could you please provide the solution i am bit confused.

Answer 3

T1	T2	T3	1
		R(a)	2
	W(a)		3
R(a)			4
		W(a)	5
W(a)			6

T1 should execute always in last( for last write rule)
T3 should come always first ( for initial read)
then possible order is only one T3->T2->T1  => 1
but here when T3 come first then W(a) of T3 can be put in 2 places(at 5 and between (2,3)) without affecting other Read/write 
So total view serializable schedule will be = 1 x 2 = 2