Performance Studies of Locking Protocols for Real-time Databases With Earliest Deadline First

Abstract

Transaction scheduling in real-time database systems (RTDBS) is complicated by the requirements to satisfy the timing constraints of transactions and at the same time to maintain database consistency. These two goals may not be easily achieved at the same time because of the incompatibility between the two schedulings, namely data scheduling and resource scheduling. In this paper, a new locking protocol, called Hybrid 2-Phase Locking (Hb2PL), is proposed for concurrency control in RTDBS with the objectives to maintain database consistency and to minimize its impact on the adopted resource scheduling algorithm. The performance of Hb2PL has been compared with two other well-known realtime locking protocols, High Priority 2-Phase Locking (H2PL) and Conditional High Priority 2-Phase Locking (CH2PL). Amongst the three protocols, the performance of Hb2PL is the best for different degrees of system workloads and number of CPUs. CH2PL is most sensitive towards changes in data contention and CPU preemption. The results also indicate that the effect of the protocols on the system performance is more significant under light workloads than under heavy workloads in which case the effectiveness of the resource scheduling algorithm is the dominant factor on system performance. Relationship between the optimal resource scheduling algorithm, Earliest Deadline First (EDF), and the locking protocols has also been studied. It has been found that their effect on the performance of RTDBS is significantly affected by the distribution of transaction deadlines and the deadline variability.