View the k-th percentile of a set of measurements with Silk Performer

View the k-th percentile of a set of measurements with Silk Performer

The Overview report, generated after a load test, presents some Percentile charts along with the values for 50th, 90th, 95th, and 99th percentile displayed. Is it possible to include additional Percentile charts and how to determine the k-th percentile using Silk Performer?

To include additional Percentile charts, the function “MeasureCalculateRawPercentiles” should be declared in the TInit transaction along with appropriate Measurement Functions to set or start/stop the measure. Following is a code snippet for a timer measure:

transaction TInit
begin
    MeasureCalculateRawPercentiles("Home page", MEASURE_TIMER_RESPONSETIME);

transaction TMain
begin
      MeasureStart("Home page");
      WebPageUrl("http://"+serverAddress+"/ShopItV60", "ShopIt - Greetings");
      MeasureStop("Home page");

Refer to Silk Performer Help for definition of MeasureCalculateRawPercentiles as well as an example for a custom counter measure.

Following is a screenshot of two percentile charts as shown in the Overview report:

To find out the k-th percentile (other than those shown in the report) without estimating it from the graph, open the baselineReport.brp file using a text editor.

And using the text editor search facility, locate the Percentile Data of the desired measure by searching for the name of the measure or the “PercentileData” keyword. 

Following is a sample of the Percentile Data appearing in the baselineReport.brp:

In Silk Performer, there are one hundred markers, identified by Marker nr=”0”, Marker nr=”1”, etc.

Marker nr=”0” indicates the 1st percentile;

Marker nr=”24” indicates the 25th percentile;

Marker nr=”49” indicates the 50th percentile;

Marker nr=”74” indicates the 75th percentile; and

Marker nr=”99” indicates the 100th percentile

Background

  • Percentile graphs enable you to analyze the percentages of actions that execute within certain time limits. With the help of percentile graphs you can determine the percentage of transactions, page-load times, and custom timers that meet the performance criteria defined for your system. Additionally, by considering the shape of a graph, you can analyze the distribution of execution times.

Additional Notes

  • Silk Performer offers a more precise percentile calculation than earlier releases, pre Silk Performer 9.5. To support this improved implementation, a new function named MeasureCalculateRawPercentiles is released and the original function MeasureCalculatePercentiles is deprecated. Executing the function MeasureCalculatePercentiles in Silk Performer will internally invoke the MeasureCalculateRawPercentiles with default parameters. This is mentioned in Silk Performer release notes. 

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