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Median response times off

See original GitHub issue

 Name                                                          # reqs      # fails     Avg     Min     Max  |  Median   req/s
----------------------------------------------------------------------------------------------------
 POST long                                                        1     0(0.00%)    6067    6067    6067  |    6100    0.00
 POST short                                                       1     0(0.00%)    1239    1239    1239  |    1200    0.20
----------------------------------------------------------------------------------------------------
 Total                                                           2     0(0.00%)                                       0.20

 Name                                                          # reqs      # fails     Avg     Min     Max  |  Median   req/s
--------------------------------------------------------------------------------------------------------------------------------------------
 POST medium                                                       7     0(0.00%)     468     199    1006  |     360    
 POST short                                                        2     0(0.00%)    1063     574    1553  |     570    0.33
----------------------------------------------------------------------------------------------------
 Total                                                              9     0(0.00%)                                       1.00

This only seems to be an intermittent issue, but notice how the median response times are not within the bounds of min and max. Anyone else ran into a similar issue?

Issue Analytics

State:
Created 7 years ago
Comments:8 (8 by maintainers)

Top GitHub Comments

4reactions

heymancommented, Mar 23, 2017

In order to calculate the median response time, as well as response times for specific percentiles, without storing the response time for every single request, we keep a dict of the following format: {response_time: numer_of_requests}. In order to save memory we round the response time to only use two digits of precision (so that 6067 becomes 6100, 1239 -> 1200, 574 -> 570, and so on). Since that dict is used to calculate the median response times, while the exact response times are used when calculating min/max, it could happen that the median ends up outside of the min/max boundaries (especially for few requests).

I guess it would probably be good to mention that we only use two digits precision for median & percentile response times, in the docs and the web UI.

0reactions

heymancommented, Oct 19, 2019

#790 merged