Manet-based Mobile Database Buffer And Query Optimization Techniques

With the rapid development of wireless network technology, mobile computing hasbeen applying in more and more field. Mobile database is one of the most importantarea in mobile computing, it can make people access any data in any time and any place.The appearance of MANET provides a new form for mobile database. However, we arestill facing new challenges, because of the mobile hosts, disconnection of wirelessnetwork, limited transmission bandwidth and limited host energy, in mobile databaseresearch which is based on MANET. Existing research on caching technology, queryprocessing and query optimization are not enough, and still in the beginning phase,there are many problems waiting to solve and perfect.This paper mainly studies the technologies of data caching and query optimizing inmobile data base system, which is based on MANET, presents cooperative cachealgorithm among groups(CCAG for short), a common query algorithm based on CCAGand a multi-join query algorithm using cache data(MJCD for short). Cooperative cachemechanism among groups, which is on the basis of data using, fully considers the dataaccess frequency, the distance from cache node to source node, data size and the dataconsistency, realizes data caching among groups. CCAG makes the caching data morereasonable, enhances the hit ratio of cache. The common query algorithm based onCCAG which fully makes use of the cache data in the Network, improves the queryefficiency and depresses the energy cost. MJCD algorithm, which aims at saving energycost, optimizes the multi-join query in two phases. The first phase optimizes the queryin the whole aspect, it uses dynamic programming method to get a query plan whichcost the lowest energy, The second phase optimizes the query in partial aspect, it takesaccount of available cache data to choose a best execution plan for each sub join querywhich is got from the first phase. MJCD not only remarkably reduces the energy cost ofthe query but also adjusts MANET's environment. In the end, on the basis of above algorithms, this paper implements a mobiledatabase antitype system-MDBMS which is based on MANET, and gives experimentresults and performance analyses on all the algorithms.