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2 votes
2 votes
T1 T2 T3
R(X)


W(X)
commit

W(X)
commit





R(X)
commit

 

is this transaction conflict serializable and view serializable?

 

1 Answer

Best answer
4 votes
4 votes

It is not Conflict Serializable as there is dependency between $T_1$ and $T_2$ in both the directions for conflicting operations (cycle in precedence graph).

For View Equivalence:

  1. If transaction $T_i$ reads initial value of any data item $X$ in one schedule it must do the same in all the equivalent schedules
  2. If transaction $T_i$ writes the final value of any data item $X$ in one schedule, it must do the same in all the view-equivalent schedules. 
  3. If transaction $T_i$ reads data item $X$ written by transaction $T_j$, it must do the same in all the view equivalent schedules

So, the given schedule is not View Serializable as it requires $T_1$ to come before $T_2$ to ensure $T_1$ reads first and $T_2$ to come before $T_1$ to ensure $T_1$ writes last, which is not possible. 

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