The Design And Implementation Of Query Optimizer In Database Management System

Database software is the kernel of data processing; our scientists are always trying to develop our own database management system. At the same time the vital departments such as national defense, government, finance demand a safe DBMS. So developing our own DBMS will affect China's software industry and protect national information. This paper is about the research work for "DBMS and Application" project which is the national 863 high-tech programs, introducing the module of query optimization which supports the system working in good order and with high performance.Query optimization is an important element of database manager system. After describing the architecture of our own DBMS, this paper introduce the function of query optimization, the common processing steps of OSCAR query optimization the relation with other modules. Then, this paper mainly discuss the design and implementation of OSCAR query optimization. It introduces the common rules of query optimization. Then the technique of query preprocessing and pulling sub query up is introduced. Finally, the access path selection and the account method of const evaluation are discussed in detail.Because query sentences of the same pattern has the same result of optimization in general, so it need only be optimized one time. In order to improve performance of query, we can provide a cache to save query result. It resolves the problem effectively.Based on the contents of this paper, query optimization module was implemented properly. It is a useful practice of developing our own DBMS product.