A Cost Evaluator for Parallel Database Systems

. The design of ESQL queries Optimizer may be decomposed into three dimensions: (i) the search space which defines the syntactic representation of all relevant aspects of an execution, (ii) the search strategy used to generate an optimal execution plan and (iii) the cost evaluator which calculates the metrics used by the search strategies. In this paper, we investigate issues involved in designing and using a cost evaluator, separate from the Optimizer, for queries optimization in parallel database environments. This cost evaluator can be seen as an extension of the cost evaluator of the EDS [1], DBS3 [3, 20] parallel database systems and the Papyrus project [7]. 1. Introduction Following [13, 30], we break the ESQL [8] (a conservative extension of SQL with object and deductive capabilities) queries Optimization into three phases: logical optimization, physical optimization and parallelization. Logical optimization [30] consists of two main activities: simplification (i.e. eliminatio..