The design and implementation of a full-fledged multiple DBMS

We have described our design of the multiple DBMS (MDBMS). This MDBMS enables users to access data controlled by different DBMSs as if data were managed by a single DBMS. It supports facilities for SQL queries and transactions, and considers security functions. In addition, an ODBC driver at the client site has been realized to ease the development of MDBMS applications. Several popular commercial DBMSs, including Oracle, Informix and Sybase, have been successfully integrated. The MDBMS is in operation now. However, we found the performance to be unsatisfactory. It took about several seconds to process an SQL query with single join on two relations of hundreds of tuples. We have identified the performance bottleneck to be on the retrieval of meta data. The current MDBMS Server employs a commercial DBMS to store meta data, which is necessary for processing a global query. The processing of a query is slow because it needs to retrieve the schema information via an external DBMS several times. We are currently designing a core storage manager and an access manager specifically for maintaining the meta data and the intermediate results of a global query. We expect this design to significantly improve the performance