UK Oracle User Group


Histograms in 12c

5 May 2017

UKOUG Database & RAC Cloud, Infrastructure & Availability SIG Thursday 8th June

Date: Thursday 8th June

Time: 10:45 - 11:30

Track: Database

Abstract: 

Before 12c histograms could be expensive to create and, if your data patterns were unlucky, could cause as many problems as they solved. Things are much better in 12. 

Historically Oracle gave us frequency histograms and height-balanced histograms, so we start this presentation with a brief look at their respective costs, benefits and threats, and the special cases where better strategies are needed. We then move on to looking at the enhancements to histograms that appear in 12c showing how an extension to the “approximate NDV” mechanism from 11g allows frequency (and the new, Top-N frequency) histograms to be built far more accurately and efficiently, and how the new “hybrid” histogram gives us more information with less risk using no more effort than the original height-balanced histogram.

Presented by:  Jonathan Lewis, JL Computer Consultancy

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