Processing real-time transactions in distributed mobile environments

Abstract

With the rapid advances in mobile computing technology, there is an increasing demand for processing real-time transactions in a mobile environment. In this thesis we study the concurrency control problem in mobile distributed real-time database systems (MDRTDBS). Firstly, we study the impact of mobile network on the performance of a well-know concurrency control protocol, the High Priority Two Phase Locking (HP-2PL), as compared with the conventional reliable wired network. Based on the findings and the 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. To further improve the system performance, two new strategies are proposed to reduce the impact of mobile network on the performance of the DHP-2PL: (1) A transaction shipping strategy 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 study the impact of mobile environment on the DRTDBS and evaluate the performance of the proposed transaction shipping approaches and the effectiveness of using similarity for concurrency control in MDRTDBS.