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Abstract:

We present an overview and initial performance assessment of a rule-based query optimizer written in VenusDB. VenusDB is an active-database rule language embedded in C++. Following the developments in extensible database query optimizers, first in rule-based form followed by optimizers written as object-oriented programs, the VenusDB optimizer avails the advantages of both. To date, development of rule-based query optimizers have included the definition and implementation of custom rule languages. Thus, extensibility required detailed understanding and often further development of the underlying search mechanism of the rule system. Objectoriented query optimizers appear to have achieved their goals with respect to a clear organization and encapsulation of an optimizer's elements. They do not, however, provide for the concise, declarative expression of domain specific heuristics. Our experience demonstrates that a rule-based query optimizer developed in VenusDB can be well structured, flexible, and demonstrate good performance. We compare a relational optimizer developed with Volcano and a functionally identical optimizer developed with VenusDB. The results demonstrate comparable performance on small queries with few joins, while the VenusDB optimizer scales better and outperforms Volcano on larger joinarity queries. Since we did not have to develop a specialized rule language or consider application specific programming constructs, the source code for the optimizer is small and straightforward, about one-third the size. Similar code comparisons with an object-based optimizer, the VenusDB optimizer reveals similar benefit.

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