Awesome presentations including some of my favorite presenters/authors, Tim Gorman, Cary Millsap, Debra Lilley, Dennis Horton and Deep Ram, Tanel Poder, Nadia Bendjedou and Cliff Godwin.

My Favorite presentation was from Cary Millsap on his presentation on “Skew”. Skew is everywhere. Did you know the average number of legs per person was 1.99? Why is it not greater than 2, because there are no three legged humans.

The James Bond joke, if you don’t know what a Thermos is and someone tells you that it keeps hot things hot, and cold things cold, why didn’t it work when I put my coffee and my popsicle in my thermos?  Understand your data.

Skew exists everywhere, especially in systems, charaterized by CPU, memory, disks and networks. In 11.2.0.2 there are 1118 system calls, 6 dba calls and 2 psuedo calls. The system  processes are dominated by system calls, with a few critical DBA calls.

This system basically makes calls to the system and to the database.

The main idea was to illustrate the common misconception that idle wait events can be ignored. The answer is, you have to drill down to the exac cause of the wait and not look at summary data that represents median values or averages.

Cary summarized his Method R process: Identify the Important Task, Measure the Response Time, Optimize Response, Repeat until satisfied.

Check out Simpson’s paradox, a baseball statistical conundrum. Bobby Bragan the 1966 manager of the Atlanta Braves, was quoted as saying, “If you have one foot in the oven and one foot in the icebox, the percentages would say you’re fine”.

Drill down on each issue and remove the skew from each case by understanding the details of each wait.