Seriazability

Question

Comments

Is it correct?

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Yes but how

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Let X=10, Y=15 initially and W(X) increments X by 10.

T1	T2
	R(x) //Reads X=10
	R(y) //Reads Y=15
R(x) //Reads X=10
R(y) //Reads Y=15
W(x) //Write X=10+10=20 in DB
	R(X) //Reads X=20

 

When T2 reads X first then it sees X=10. Again when it performs the same read operation now it sees X as 20. This is what we call unrepeatable read.

Answer 1

I think the answer is S1.

Unrepeatable Read- If a transaction tries to read the value of a data item twice and between the two read operations ,if another transaction updates the value of that data item then the value of the first read and second read operations will not be same.This is Unrepeatable Read.

Comments

This caes you given also possible in s2

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T2 read and update the value x but after T1 gets a updated value means x values will be different