Transaction processing in an asymmetric mobile environment

Pao Yue-kong Library Electronic Theses Database

Transaction processing in an asymmetric mobile environment


Author: Mok, Siu-yu Eppie
Title: Transaction processing in an asymmetric mobile environment
Degree: M.Sc.
Year: 2000
Subject: Mobile computing
Transaction systems (Computer systems)
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Dept. of Computing
Pages: v, 85 leaves : ill. ; 31 cm
Language: English
InnoPac Record:
Abstract: Recently the demand of mobile computing has increased. Not only the laptop becomes lighter, but also it has the ability to access data regardless of location. This allows transactions, e.g. banking or stock transactions, to be done through the laptop. Mobile clients may issue transactions simultaneously and the server is required to handle such requests. This thesis focuses on transaction processing in mobile database. A transaction is an execution of program that accesses a shared database. When two or more transactions execute concurrently, their database operations execute in an interleaved manner. This interleaving may lead to an inconsistent database state. Concurrency control protocol is one that synchronizes concurrent transactions to ensure consistency. In many application domains, the downstream capacity from servers to clients is much greater than the upstream communication capacity from clients back to servers. We refer to these environments as Asymmetric Communication Environments. Our model consists of a database server managing a collection of data items. Users are connected to the server via one of the two types of channels: point-to-point and broadcast. For data items which are of interest to a majority of users, they will be periodically broadcast to all users. In a mobile environment, users may disconnect from the server due to run out of battery, expensive connection charges, etc. The data items that clients receive are cached in their local disk so that they can continue to work even when they become offline. Since the cache size is limited, cache replacement algorithm should be considered. We have proposed a protocol which is an extension of traditional optimistic concurrency control protocol, but in the context of mobile environment. Optimistic concurrency control protocol is a concurrency control protocol that assumes the conflicts among transactions are rare. Our algorithm is then generalized and improved. The performance of the protocol and the asymmetric communication behavior of the mobile environment as well as the energy consumption are studied. The simulation model is built based on CSIM. Simulation results would be presented, followed by interpretation and discussion of results.

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