View serializable

Question

S: r1(x),r2(x),w1(x),w2(x) it is view serializable or not

Comments

can u plz say why it is not view serializible??

---

T1 and T2 are the initial read for a

Am Irightt

---

Yes, initial read condition is violated

Answer 1

The given schedule is not conflict serializable so now check for blind writes , if u get blind writes then the schedule may or may not be view serializable but if there are no blind writes then the schedule cannot be view serializable .And here we don't have any blind writes so the schedule is not view -equivalent to any serial schedule .

Answer 2

This schedule is not conflict serializable. Now we check for blinbd writes. Yes it has blind writes w1(x),w2(x). Now T1 says it reads initial value of x so in equivalent serial schedule T1 should occur first. Also the given schedule says T2 also reads initial value of x so in equivalent serial schedule T2 should occur first. So T1 occurs first before T2 and T2 occurs first before T1 which is actually not possible so given schedule is not view serializable. Also we can do by manually writing the schedules. As two transactions are there so possible serial schedules are

 

a) T1-->T2 r1(x),w1(x),       r2(x),w2(x)   - Here we see that T1 is reading initial value of x,the final write condition by T2 has been mainained  bt T2 is unable to read initial value of x as it is modified by T1's w1(x).

 

b)T2-->T1   r2(x),w2(x),       r1(x),w1(x)   - Here we see that T2 is reading initial value of x, BUT the final write condition by T2 is not  mainatined and also T1 is unable to read initial value of x as it is modified by T2's w1(x).

 

So  IT IS NOT VIEW SERIALIZABLE.

PLS CORRECT ME IF I WRONG