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The button determines whether the numeric metric displays are denominated as rates or cumulative summaries.
 

Note that time graph displays always display the metrics as rate (per second), regardless of the button selection. Furthermore, in all windows, the TOP are selected using TOTAL. The fact that you select Rate, or per-interval or per-execution only affects the numbers displayed, not the selection of the records.

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Total - The default display. The metric values are the total over the selected period.

Select this option if you are interested in the total period activity.

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Rate (Per Interval) - Rate per window-defined resolution (see time range), allowing for comparison and statistical (average and high values) calculation per interval.
 

Select this option when the per-second option values yield values too low for ready comparison.

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Rate (Per Second) - Metric parameters in the list pane are calculated as an average per second for the selected time frame, allowing for comparison and statistical (average and high values) calculation. All graphical displays are based on this calculation method.
 

Select this option for ease of inter-period comparison.

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Per Execution - Metric parameters in the list pane are calculated as an average per SQL-statement execution.
 

Select this option when interested in the impact of a SQL statement execution.

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