Cost-Based Optimization for Magic: Algebra and Implementation

Magic sets rewriting is a well-known optimization heuristic for complex decision-support queries. There can be many variants of this rewriting even for a single query, which differ greatly in execution performance. We propose cost-based techniques for selecting an efficient variant from the many choices. Our firstcontribution is a practicalschemethat modelsmagic sets rewriting as a specialjoin method thatcan be added to any cost-based query optimizer. We derive cost formulas that allow an optimizer to choose the best variant of the rewriting and to decide whether it is beneficial. The order of complexity of the optimization process is preserved by limiting the search space in a reasonable manner. We have implemented this technique in IBM's DB2 C/S V2 database system. Our performance measurements demonstrate that the costbasedmagic optimization techniqueperforms well, and that without it, several poor decisions could be made. Oursecondcontribution is a formal algebraicmodelof magi...

• Type: Conference
• Year: 1996
• Where: SIGMOD
• Authors: Praveen Seshadri, Joseph M. Hellerstein, Hamid Pirahesh, T. Y. Cliff Leung, Raghu Ramakrishnan, Divesh Srivastava, Peter J. Stuckey, S. Sudarshan
• Keywords: Complex Decision-support Queries, Cost-based Query Optimizer, Database, Magic Sets, SIGMOD 1996