The simplicity of a dimensional model also has performance benefits. Database optimizers process these simple schemas with fewer joins more efficiently. A database engine can make strong assumptions about first constraining the heavily indexed dimension tables, and then attacking the fact table all at once with the Cartesian product of the dimension table keys satisfying the user's constraints. Amazingly, using this approach, the optimizer can evaluate arbitrary n-way joins to a fact table in a single pass through the fact table's index.
- Chapter 1: Data Warehousing, Business Intelligence, and Dimensional Modeling Primer
- from The Data Warehouse Toolkit: The Definitive Guide to Dimensional Modeling, 3rd Edition
- Publisher: John Wiley & Sons
- Released: July 2013
Is there a point to be made here about how this pattern maps to MapReduce
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