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Question

Consider the following schedule:
S : r2(z), r2(y), w2(y), r3(y), w3(z), r1(x), w1(x), w3(y), w3(z), r2(x), r1(y),
w1(y), w2(x)

is this sechedule serializable ??

Answer 1

Schedule is not Serial, not even Conflict Serial..

Cheking Vew Serial :

X initially read data from  database so X should execute before Y & Z bcoz Y & Z both update x value..

X ----> {Y,Z}        .............(1)

Final write of y done by transaction X. That means X should execute after Y & Z because both write y.

{Y,Z } ----> X.      ..............(2)

(1) & (2) contradict each other ..

So schedule is not  View Serial..

Non serialisable schedule..

Comments

sir ,can we proceed in this way :

first we check is it Conflict serializable schedule !than if it is CSS than we can say it is view serializable which means it is SERILIZABLE SCHEDULE.???

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Checking order should be : Serial ---> CSS ---> VSS

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thanx

Answer 2

Its not a conflict nor view serializable .