Calculating graph points on a performance curve
During a test run, multiple graphs collect performance metrics. Each graph has multiple curves. Each curve has data points calculated based on the graph sample rate controlled by the Graph sample rate (s) property in the Other Options -> Advanced Options section, as shown below.
The sample rate is the number of seconds between the previous and the next sample timestamps. During a test run, on every sample timestamp, a new data point is added to every performance curve based on data collected from the previous sample timestamp. For example, for a requests/sec KPI curve, the next data point will be calculated by taking the number of requests from the previous data point and dividing it by the sample rate.
Each load agent is queried on every sample timestamp in a distributed test. Decreasing the sample rate will give more granular data points but may impact the controller's performance. Setting the Graph sample rate property (s) to at least 10 during a distributed test is recommended.
Reading the graph
Every performance graph has one or more graph curves. Each curve has its own units. For example, the requests/second and average response time curves have different units in a KPI graph. To plot multiple different unit curves on one graph, StresStimulus uses ranges.
- Each curve has a range value which is displayed in the Range column (a).
- The y-axis (b) of the graph is a percentage (0-100%) of the range.
- A point's actual value is plotted as the percentage of the range on the graph. To see the actual value of the data point (d), mouse over the data point to see the tooltip.
Re-scaling the curve
During the test, if the point's value falls outside the curve's range, the range is increased by order of magnitude, and all data points are rescaled.
- The Min column represents the minimum graph point value
- The Max column represents the maximum graph point value
- The Avg column represents the average of graph point values
The Last column represents the last graph point value.
Additional grid fields
Some graphs have additional grid fields that are described here.
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