Improvement of the Performance of a Query Optimization for Distributed System

Query processing is an important concern in the field of distributed databases. The main problem is: if a query can be decomposed into sub queries that require operations at geographically separated databases, determine the sequence and the sites for performing this set of operations such that the operating cost (communication cost and processing cost) for processing this query is minimized. The problem is complicated by the fact that query processing not only depends on the operations of the query, but also on the parameter values associated with the query. Distributed query processing is an important factor in the overall performance of a distributed database system. Query optimization is a difficult task in a distributed client/server environment as data location becomes a major factor. In order to optimize queries accurately, sufficient information must be available to determine which data access techniques are most effective (for example, table and column cardinality, organization information, and index availability). Optimization algorithms have an important impact on the performance of distributed query processing.