A window-based object allocation and replication algorithm for real-time distributed database systems in mobile computing environment

A real-time distributed database system (RTDDBS) must maintain the consistency constraints of objects and must also guarantee the deadline imposed by each arriving request. Servicing these requests may incur I/O costs, control-message transferring costs or data-message transferring costs. In this paper, we consider our system in the mobile computing environment, where the link bandwidth is very limited and hence the transfer of data-messages and control-messages over the wireless network incurs very high cost when compared to I/O cost. Thus, we present a mathematical model that considers the communication costs (control-message/data-message transferring cost) associated with the servicing of a request. Using this cost model, our objective is to service the arriving requests on or before their respective deadline periods and minimize the total communication cost. To this end, we design an adaptive object allocation and replication algorithm, referred to as Real-Time Distributed Dynamic Window Mechanism (RDDWM), that adapts to the random patterns of read-write requests. Using competitive analysis, we study the performance of RDDWM algorithm under two extreme conditions.