Transaction scheduling in distributed real-time systems

In this paper, we study the performance of using optimistic approach to con currency control in distributed real-time database systems (RTDBS). The tra ditional optimistic approach suffers from the problem of unnecessary restar ts. Transaction restarts can significantly increase the system workload and intensify resource and data contention. In distributed environments, the c omplexity of the system and the high communication overhead exacerbate the problem. Therefore, the number of unnecessary restarts is the determinant f actor that affects the performance of optimistic approach in distributed RT DBS. When optimistic approach is extended to distributed environments, a nu mber of issues resulting from the increased complexity and communication ov erhead have to be resolved. In this paper, a new real-time distributed opti mistic concurrency control (DOCC) protocol with dynamic adjustment of seria lization order (DASO), called DOCC-DA is proposed. This protocol can avoid unnecessary transaction restarts by dynamically adjusting the serialization order of the conflicting transactions. Therefore, resources can be saved a nd more transactions can meet their deadlines. In the DOCC-DA protocol, a n ew distributed circular validation scheme is included to facilitate transac tion validation in distributed environments. The performance of the DOCC-DA protocol has been examined in detail by simulation. The results showed tha t the performance of the DOCC-DA protocol is consistently better than that of other protocols.