JL Computer Consultancy
Boundary Conditions on Cost Calculations |
August 2006 |
Those of you who have followed the Addenda and Errata pages for my book “Cost Based Oracle Fundamentals” will be aware of the contributions made by Alberto Dell’Era to the addenda on Join Cardinality.
Recently Alberto sent me a note with a URL pointing to some other work he had done investigating the selectivity calculations with particular relevance to predicates close to – and outside – the boundary values recorded under the column statistics. This is an important issue, of course, since many applications revolve around queries for “the most recent data”, which leaves the optimizer dealing with exactly those queries most likely to be at, or past, the boundary values.
Rather than trying to say anything about the conclusions, I thought it appropriate to point you to the relevant URL so you could read the entire set of articles. There are several linked pages, but the discussion starts here.
