The Volcano optimizer generator: extensibility and efficient search

The Volcano project, which provides efficient, extensible tools for query and request processing, particularly for object-oriented and scientific database systems, is reviewed. In particular, one of its tools, the optimizer generator, is discussed. The data model, logical algebra, physical algebra, and optimization rules are translated by the optimizer generator into optimizer source code. It is shown that, compared with the EXODUS optimizer generator prototype, the search engine of the Volcano optimizer generator is more extensible and powerful. It provides effective support for non-trivial cost models and for physical properties such as sorting order. At the same time, it is much more efficient, as it combines dynamic programming with goal-directed searching and branch-and-bound pruning. Compared with other rule-based optimization systems, it provides complete data model independence and more natural extensibility.<<ETX>>