Calibrating the Query Optimizer Cost Model of IRO-DB,

an Object-Oriented Federated Database System*

20/06/1996

Georges Gardarin, Fei Sha, Zhao-Hui Tang

PRiSM Laboratory,
University of Versailles,
45 Avenue des Etats-Unis
78035 Versailles Cedex, FRANCE

email : <Firstname>.<Lastname>@prism.uvsq.fr

Abstract Providing integrated access to multiple, distributed and heterogeneous data sources has become one of the major issue in database research and industry. Being a major European Esprit project started in 1993, IRO-DB is experimenting an on-demand solution to this problem. IRO-DB is an object-oriented federated database system to access multiple data sources from an ODMG compliant C++ interface. The system encompasses several components, including local database adapters to homogenize local data sources, a remote object access component to query and transfer collections of objects from site to site, and a mediator to define integrated views, decompose and optimize queries, and combine results. A first version is currently operational with a simplified query optimizer not using a cost model. This paper gives an overview of the IRO-DB architecture and describes in details the cost evaluator currently under elaboration for the next version of the distributed query optimizer. The cost model is composed of a set of mathematical formulas with coefficients to estimate the cost of the search operators. The coefficients are deduced from a calibrating object-oriented database composed of linked collections of objects. A tuning application is run on each local site to adjust the cost formulas and fix the coefficients. We report on the tuning of O2 and ObjectStore. We show that the estimation is quite accurate for path traversals with the OO7 benchmark on top of ObjectStore.

Keyword : Cost Model, Object, Calibrating, Heterogeneous, Path Expression

* This work is initiated and partially supported by the European IRO-DB ESPRIT project. The project is developed in cooperation with GMD, GOPAS, IBERMATICA, EDS, GRAPHAEL, INTRASOFT and O2 Technology. PRiSM acts as a subcontractor of both GRAPHAEL and EDS.