90th percentile accuracy in JMeter

2
votes

I have seen some 'odd' results in JMeter when it comes to calculating the 90th percentile response time from a test. I have a results.jtl from a one hour test, with approximately 20,000 data points per transaction. If I use the file to generate a dashboard with;

jmeter -g results.jtl -o c:\temp\report

I can see I get a 90th response time of 2261.10. If I look at the same results.jtl file through the aggregate report in JMeter (post test), I have 2260. I also used the percentile function in Excel which gave me 2260.3 (which ties in with the aggregate report). The 95th percentile is similar, I get 3551.50, 3549 and 3549.3 from each of the three calculations.

Has anyone else seen this type of discrepancy between reports? Is there anything I can do to correct the dashboard?

1
jmeter

1 Answers

0
votes

The differences are due to approximation that is made by JMeter when computing the report.

This can be adjusted by increasing the value of this property:

jmeter.reportgenerator.statistic_window=20000

See this doc and this blog:

By default JMeter tries not to consume too much memory.