INDUSTRIAL-STRENGTH PARALLEL QUERY OPTIMIZATION - ISSUES AND LESSONS

In the industrial context of the EDS project, we have designed and imp lemented a query optimizer which we have integrated within a parallel database system. The optimizer takes as input a query expressed in ESQ L, an extension of SQL with objects and rules, and produces a minimum cost parallel execution plan. Our research agenda has focused on sever al difficult problems: support of ESQL's advanced features such as pat h expressions and recursion, modelling of parallel execution spaces an d extensibility of the search strategy. In this paper, we give a retro spective on the optimizer project with emphasis on our design goals, r esearch contributions and implementation decisions. We also describe t he current optimizer prototype and report on experiments performed wit h a pilot application. Finally, we present the lessons learned.