https://bz.apache.org/bugzilla/show_bug.cgi?id=65446
Bug ID: 65446
Summary: Report / Dashboard: Percentile over time values depend
on the order of the data even with large window size
Product: JMeter
Version: 5.4.1
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P2
Component: Main
Assignee: [email protected]
Reporter: [email protected]
Target Milestone: JMETER_5.5
We have a use case where we are merging CSV files from two different,
independent JMeter instances and using the combined CSV file to generate the
dashboard. While merging two files, there is obviously a question about the
order of the data points in the CSV and how it impacts the final dashboard. To
test it out, I created two CSV files with the same data but one where the data
is in increasing order of timestamps and the other is in decreasing order and
compared the Response Time Percentiles Over Time (successful responses) graphs.
>From what I understand from Kth select algorithm used for percentile
calculation, if the input data set contains of the same values, irrespective of
the order, the output should be the same every time. In JMeter, the input data
set is controlled by the jmeter.reportgenerator.statistic_window property.
So, my hypothesis is, if the statistic_window is large enough to hold all the
samples for a given time-granularity window, the output graphs should be 100%
identical but that doesn't seem to be the case. I generated graphs with a
statistic_window of 100 million which is far more than the number of samples in
the entire CSV file and still, the graphs are different from one another, even
if it is by a small percentage.
I like to understand if my assumptions are wrong or if there is a bug in JMeter
that I need to search for.
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