The kill-wait concurrency control combines the concepts of the immediate update concurrency control and the timestamp-ordered control. As in the timestamp-ordered system, when a transaction, T1 is initiated, it is assigned a timestamp, TS(T1). However, the system uses the same conflict table as the immediate-update pessimistic control does and resolves conflicts using the rule

If transaction T1 makes a request that conflicts with an operation of active
transaction, T2
if TS(T1) < TS(T2), then abort T2, else make T1 wait until
T2 terminates.
where abort T2 is referred to as a kill because T1 kills T2.

a. Showthat the kill-wait control serializes in commit order.
b. Give a schedule produced by a kill-wait control that is not serializable in timestamp order.
c. Explain why deadlock does not occur in a kill-wait control.

a. It serializes in commit order because transactions that are not aborted are granted
requests or wait using the same locking protocol used in an immediate-update
pessimistic control.
b. w1(x) w2(y) commit2 r1(y) w1(z ) commit1
T2 started after T1 but is serialized before T1.
c. Since a transaction waits only for an older transaction, there can be no cycle of
waits.