2.14.5 Serial Equivalence

Definition: Two transactions are serial if all the operations in one transaction precede the operations in the other.

eg the following actions are serial

R_i(x)W_i(x)R_i(y)R_j(x)W_j(y)

Definition: Two operations are in conflict if:

• At least one is a write
• They both act on the same data
• They are issued by different transactions

R_i(x)R_j(x)W_i(x)W_j(y)R_i(y) has R_j(x)W_i(x) in conflict

Definition: Two schedules are computationally equivalent if:

• The same operations are involved (possibly reordered)
• For every pair of operations in conflict, the same operation appears first in each schedule

So, a schedule is serialisable if the schedule is computationally equivalent to a serial schedule.

Question: Is the following schedule for these two transaction serially equivalent?

R_i(x)R_i(y)R_j(y)W_j(y)R_i(x)W_j(x)W_i(y)