Data Management For The Client In Mobile Real-time Database

The study of traditional distributed computing and distributed database is based on limited network and fixed host. It adopts some tolerant crytic hypothesis, such as fixed network connecting, peer to peer communication cost, fixed host etc. With the development of mobile communication technology and internet technology, and the popularity of mobile computing, many computing node can connect with network as they move. Then above-mentioned conditions do not exist any more. The technology of traditional distributed database cannot apply to mobile database absolutely. So there bring the concepts of "mobile computing" and "mobile database", which are becoming the new research in the area of database. In this paper, some related technology about data management for the client in mobile real-time database is investigated, including data broadcast, data hoarding, data cache and consistency maintenance.The pivotal problem of data broadcast technology is the problem of data broadcast scheduling, the key are scheduling algorithm and ascertaining cycle of broadcast to optimize database performance. In this paper, the optimization values of two parameters which are access time and tuning time scaling for data broadcast scheduling algorithm are deduced. The advantage of multi-disk scheduling algorithm is analyzed by comparison. A multi-disk scheduling algorithm which can keep low access time as tuning time optimized is designed. Problems about disk partition and broadcast frequency brought by this algorithm are resolved.Data hoarding technology means the technology of prefetching data which may access by user after disconnection later to cache. In this paper, merits and demerits of PIU algorithm which is a view update algorithm based on the dynamic data freshness priority are analyzed. On this ground, an improved PIU algorithm presented, in order that view at mobile host can get as much freshness as possible in as short time as possible when disconnection or low connection happens. It effectively improves the user-oriented, real-time and consistency problem in the data on the client of mobile real-time database, providing the service of accessing data on database through wireless network for users better.Cache is necessary at mobile host to satisfy the real-time of users' accessing database on the server through wireless network. It is determined by the character of mobile computing environment. Then bring the problems of cache and consistency maintenance. In this paper, cache granularity is ascertained by comparison. Then cache working mechanism is investigated based on this. According to the requirement of cache weak consistency, weak consistency caching is proposed to resolve the disconnection caused in wireless environment. It retrenches the network bandwidth by broadcasting update reports and sending update reports.