Unable to sustain stable requests rate

Grafana k6
1

Hi.

I’m running K6 to load-test an external vendor’s API. I have been getting rather wild fluctuations in requests rate. We monitor the requests rate using statsd and new relic.

To check if the problem is on our end, I ran some tests against a mock server. I added a delay in this mock server’s request handling to simulate the response time. I found that as I increased the delay, the requests rate got more unstable.

For example, for one group of requests (CreateFoWithLatLong-AU), our target was to sustain 2000 iterations/min. However, we got:

  • with a 1s delay, requests rate hovered between 1.91 - 1.97 k iters/min
  • with a 3s delay, requests rate hovered between 1.78 - 1.89 k iters/min

I checked that:

  • it was not due to insufficient CPU/memory
  • there was still available VUs (*see CreateFoWithLatLong-AU - 203/300 VUs)
running (10m06.4s), 260/814 VUs, 87321 complete and 0 interrupted iterations
CreateCustomer-AU            [  67% ] 06/10 VUs    10m06.4s/15m0s  5.00 iters/s
CreateCustomer-SG            [  67% ] 11/20 VUs    10m06.4s/15m0s  11.00 iters/s
CreateCustomer-TH            [  67% ] 4/7 VUs      10m06.4s/15m0s  3.33 iters/s
CreateFoWithLatLong-AU       [  67% ] 203/300 VUs  10m06.4s/15m0s  33.33 iters/s
CreateOrder-AU               [  67% ] 02/25 VUs    10m06.4s/15m0s  1.67 iters/s
CreateOrder-SG               [  67% ] 06/50 VUs    10m06.4s/15m0s  3.67 iters/s
CreateOrder-TH               [  67% ] 02/15 VUs    10m06.4s/15m0s  1.12 iters/s
QueryCustomer-AU             [  67% ] 06/10 VUs    10m06.4s/15m0s  5.00 iters/s
QueryCustomer-SG             [  67% ] 11/20 VUs    10m06.4s/15m0s  11.00 iters/s
QueryCustomer-TH             [  67% ] 4/7 VUs      10m06.4s/15m0s  3.33 iters/s
QueryVirtualPosition-AU      [  67% ] 005/300 VUs  10m06.4s/15m0s  61.10 iters/s
QueryVirtualPosition500-AU   [  67% ] 01/50 VUs    10m06.4s/15m0s  5.00 iters/s

Would anyone have any insight into what is causing the unstable requests rate?

3

Hi @pfu :wave:

Welcome to the support forum, and apologies for coming back to this so late :bowing_man:

Could you show us an example script that would reproduce the issue you’re experiencing? It would be tricky to make assumptions about what might happen without a somewhat clear picture of what the script does.

Thank you :bowing_man:

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