Query regarding the Group stats calculation

I wanted to understand how the group stats are being calculated in gatling since the documentation present on the website is not very clear.

Suppose i have two groups(“Group1” & “group2”) in my scenario with 5 users ramped up.

Group1 has following 2 requests with the following stats ( which were calculated by gatling in the html report )

1.Name - request1
Total requests -5
KO -0
Mean resp. time - 5000 and so on…
2. Name - request 2
Total requests - 10
OK -5
Mean Resp. Time - 4000 and so…

So i wanted to know how the group stats will be calculated by gatling?

I calculated the mean resp. time of the group using the formula- totalRequests*MeanResponseTime of the request/Sum of all the requests in the group

i.e (5 x 5000 + 10 x 4000)/(5+10)
and the numbers were not matching the mean response time of the group calculated by gatling.

I also checked with the formula = sum of MeanResponseTime of all the requests in a group/Sum of all the requests in the group

i.e (5000+4000)/(5+10)
and still the number was not matching the mean response time of the group calculated by gatling.

So can you please clarify and explain how gatling understands this and how the stats are calculated in a more detailed way (P:s- i have gone through the documentation and still it is very unclear about the actual calculation)
Gatling version being used - 3.7.6

cc- @slandelle

Please check Gatling - Timings

Group timings can’t be computed from request timings, even means.

@slandelle The documentation here is not very detailed. So can you explain what all parameters are considered instead of request stats for the calculation? Because we need to verify on what basis its being done for analysing the results.

Also one more thing on the website

Response Time#

The response time of a group is the cumulated response times of each individual request in that group.
It is said that the group response time will be the cumulative of each individual request.

So why Group timings can’t be computed from request timings?

You’re getting the group stats wrong.

Group stats are NOT request stats aggregated for all the requests of a group.

For a given group execution:

  • the cumulated response time is the total time traffic was flying
  • the group duration is the time between the instant the virtual user enters and the instant it exists

In short, cumulated response time = group duration - pauses.

mean(group) is equal to mean(req1) + mean(req2) ONLY IF each group always consists of the same number of req1 and req2, which your 5 and 10 weights seem to refute.

Regarding percentiles, you can’t aggregate percentiles, period.

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