Which one of the following statements about the schedules is TRUE?

To check conflict serializability, we construct the precedence graph for each schedule:

For Schedule S1:

• Conflict on $X$: $r_3(X)$ is followed by $w_1(X) \implies T_3 \to T_1$

• Conflict on $Y$: $r_2(Y)$ is followed by $w_3(Y) \implies T_2 \to T_3$

• Conflict on $Z$: $w_2(Z)$ is followed by $r_1(Z)$ and $w_1(Z) \implies T_2 \to T_1$

The precedence graph has edges $T_2 \to T_3 \to T_1$ and $T_2 \to T_1$, which is acyclic. Therefore, S1 is conflict-serializable.

For Schedule S2:

• Conflict on $X$: $r_3(X)$ is followed by $w_1(X) \implies T_3 \to T_1$

• Conflict on $Y$: $r_2(Y)$ is followed by $w_3(Y) \implies T_2 \to T_3$

• Conflict on $Z$:

  • $r_1(Z)$ appears before $w_2(Z) \implies T_1 \to T_2$

  • $w_2(Z)$ appears before $w_1(Z) \implies T_2 \to T_1$

This creates a cycle ($T_1 \to T_2 \to T_1$). Therefore, S2 is not conflict-serializable.

Hence, only S1 is conflict-serializable (A).