Consider a schedule of transactions $T_1$ and $T_2$: Here, RX stands for “Read(X)” and WX stands for “Write(X)”. Which one of the following schedules is conflict equivalent to the above schedule?

Two schedules are conflict equivalent if they involve the same set of operations and order every pair of conflicting operations in the exact same way.

Let us identify the conflicting pairs between $T_1$ and $T_2$ in the given schedule:

1. On data item $B$:

   • $T_2: R(B)$ occurs before $T_1: W(B)$ $\implies T_2 \rightarrow T_1$

   • $T_2: W(B)$ occurs before $T_1: W(B)$ $\implies T_2 \rightarrow T_1$

2. On data item $D$:

   • $T_2: R(D)$ occurs before $T_1: W(D)$ $\implies T_2 \rightarrow T_1$

3. On data item $C$:

   • $T_1: R(C)$ occurs before $T_2: W(C)$ $\implies T_1 \rightarrow T_2$

Now check the given options:

• In Schedule (A):

  • On $B$: $T_2$'s $R(B)$ and $W(B)$ precede $T_1$'s $W(B)$ ($T_2 \rightarrow T_1$ maintained).

  • On $D$: $T_2$'s $R(D)$ precedes $T_1$'s $W(D)$ ($T_2 \rightarrow T_1$ maintained).

  • On $C$: $T_1$'s $R(C)$ precedes $T_2$'s $W(C)$ ($T_1 \rightarrow T_2$ maintained).

Since all conflicting operation pairs preserve the exact same relative ordering, schedule (A) is conflict equivalent to the given schedule.