Presenting Percentages

Today, a quick performance comparison came back to bite me, and it was all about percentages.

A few days ago, I was asked to do a quick comparison between two (2) test runs using AWR data. So, I produced a report similar to the following:

Metric Run #1 Run #2
% CPU Usage 0.3 0.3
% DB Time on User I/O 53.0 14.0
% DB Time on Network O/H 8.0 8.0
% DB Time as CPU 39.0 78.0

What I had hoped to say was that the second run had less User I/O overhead (O/H) than the first one.

What people read was that the second run was more CPU using than the first.

It was only after I produced a chart similar to the following that people got the message:


They could see that there was the same amount of CPU time consumed in both runs thereby giving the same overall CPU Usage % figure. And most noticeably, the biggest improvement between the two (2) runs was the big drop in the amount of time that the database engine spent waiting for User I/O.

Next time, I should spend some more time creating charts to accompany the raw figures.


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