Query Optimization in Distributed Databases

摘要

Distributed database management systems (DDBMS) are amongst the most important and successful software developments in this decade. They are enabling he computing power and data to be placed within the user environment close to the point of user activities. The performance efficiency of DDBMS is deeply related to the query processing strategies involving data transmission over different nodes through the network. This thesis is to study the optimization of query processing strategies in a distributed databases environment. With the objective of minimum communication cost, we have developed a mathematical model to find a join-semijoin program for processing a given equi-join query in distributed homogeneous relational databases. Rules for estimating the size of the derived relation is proposed. The distributed query processing problem is formulated as dynamic network problem. We also extend this model to consider both communication cost and local processing cost. We extend this model to query processing in a distributed heterogeneous databases environment. A heterogeneous database communication system is proposed to integrate heterogeneous database management systems to combine and share information. The use of a database communication system for heterogeneous DBMSs makes the overall system transparent to users from an operational point of view. Problems of schema translation and query translation of the query processing in this environment are studied.