Solving Local Cost Estimation Problem for Global Query Optimization in Multidatabase Systems

To meet users' growing needs for accessing pre-existing heterogeneous databases, a multidatabase system (MDBS) integrating multiple databases has attracted many researchers recently. A key feature of an MDBS is local autonomy. For a query retrieving data from multiple databases, global query optimization should be performed to achieve good system performance. There are a number of new challenges for global query optimization in an MDBS. Among them, a major one is that some local optimization information, such as local cost parameters, may not be available at the global level because of local autonomy. It creates difficulties for finding a good decomposition of a global query during query optimization. To tackle this challenge, a new query sampling method is proposed in this paper. The idea is to group component queries into homogeneous classes, draw a sample of queries from each class, and use observed costs of sample queries to derive a cost formula for each class by multiple regression. The derived formulas can be used to estimate the cost of a query during query optimization. The relevant issues, such as query classification rules, sampling procedures, and cost model development and validation, are explored in this paper. To verify the feasibility of the method, experiments were conducted on three commercial database management systems supported in an MDBS. Experimental results demonstrate that the proposed method is quite promising in estimating local cost parameters in an MDBS.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44824/1/10619_2004_Article_181758.pd

MULTIDATABASE GLOBAL QUERY OPTIMIZATION

Data requests ro mulriaiztabase (MDBSs) are posed through non-procedural languages such as SQL and for a global data request optimization must be performed to achieve good system performance. However, the issues are ofren complicated in multidatabases, due to addirional issues arising because of the autonomy and heterogeneity restrictions of the independent local DBMSs. The data translation problem between various local systems can be observed at the schema level and at the instance level. We have identified the need for a domain translation table in mulridatabase query processing and discuss methods of implementing it. Some observations about multidatabase inter-site joins are made and fou