CONCURRENCY CONTROL IN MOBILE DISTRIBUTED REAL-TIME DATABASE SYSTEMS

With the rapid advances in mobile computing technology, there is an increasing demand for processing real-time transactions in a mobile environment. This paper studies concurrency control problem in mobile distributed real-time database systems (MDRTDBS). Based on the High Priority Two Phase Locking (HP-2PL) scheme, we propose a distributed real-time locking protocol, called Distributed High Priority Two Phase Locking (DHP-2PL), for MDRTDBS. In the protocol, the characteristics of a mobile computing system are considered in resolving lock conflicts. Two strategies are proposed on further improve the system performance and to reduce the impact of mobile network on the performance of the DHP-2PL): (1) A transaction shipping approach is proposed to process transactions in a mobile environment by exploring the well-defined behavior of real-time transactions. (2) We explore the application semantics of real-time database applications by adopting the notion of similarity in concurrency control to further reduce the number of transaction restarts due to priority inversion, which could be very costly in a mobile network. A detailed simulation model of a MDRTDBS has been developed, and a series of simulation experiments have been conducted to evaluate the performance of the proposed approaches and the effectiveness of using similarity for concurrency control in MDRTDBS.