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Conference Paper

On the Optimal Ordering of Maps, Selections, and Joins Under Factorization


Neumann,  Thomas
Databases and Information Systems, MPI for Informatics, Max Planck Society;

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Neumann, T., Helmer, S., & Moerkotte, G. (2006). On the Optimal Ordering of Maps, Selections, and Joins Under Factorization. In Flexible and efficient information handling : 23rd British National Conference on Databases, BNCOD 23 (pp. 115-126). Berlin, Germany: Springer.

Cite as: https://hdl.handle.net/11858/00-001M-0000-000F-23A1-A
We examine the problem of producing the optimal evaluation order for queries containing joins, selections, and maps. Specifically, we look at the case where common subexpressions involving expensive UDF calls can be factored out. First, we show that ignoring factorization during optimization can lead to plans that are far of the best possible plan: the difference in cost between the best plan considering factorization and the best plan not considering factorization can easily reach several orders of magnitude. Then, we introduce optimization strategies that produce op- timal left-deep and bushy plans when factorization is taken into account. Experiments (1) confirm that factorization is a critical issue when it comes to generating optimal plans and (2) we show that to consider factorization does not make plan generation significantly more expensive.