Research in the concurrency control of real-time data access over mobile networks is receiving growing attention. WIht possible lengthy transmission delay nd frequent idsconnection, traditioal concurrency control mechanisms may become vry costly and time-consuming in mobile distributed real-time database systems. Due to limited bandwidth and unpredictable behavior of mobile networks, the past research on concurrency control for distributed real-time database systems can not be directly applied to MDRTDBS. in this paper, we propose a distributed real-time locking protocol, called SDHP-2PL, based on the High Priority Two Phase Locking Scheme and the concept of similarity for MDRTDBS. We considr the characteristics of obile networks and adopt the concept of similrity to reduce the possibility of lock ocnflicts. A detailed model of a MDRTDBS has been developed, and a series of simulation experiments have been conducted to evaluate the capability fo SDHP-2PL and the effectiveness of using similarity for MDRTDBS. The simulation results have confirmed our belief that the use of siilarity as the correctness criterion ofr ocncurrency control in MDRTDBS can significantly improve the system peroformance.
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