Consider the following four schedules due to three transactions (indicated by the subscript) using read and write on a data item $x$, denoted by $r(x)$ and $w(x)$respectively. Which one of them is conflict serializable?
- $r_1(x);r_2(x);w_1(x);r_3(x);w_2(x)$
- $r_2(x);r_1(x);w_2(x);r_3(x);w_1(x)$
- $r_3(x);r_2(x);r_1(x);w_2(x);w_1(x)$
- $r_2(x);w_2(x);r_3(x);r_1(x);w_1(x)$
- $1$
- $2$
- $3$
- $4$