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Comment by diroussel | Hacker News Reader

Did you consider wrk2?

Maybe you duplicated some of these fixes?

Yea, I looked it wrk2 but it was a no-go right out the gate. From what I recall the changes to handle coordinated omission use a timer that has a 1ms resolution. So basically things broke immediately because all requests were under 1ms.

so twrk doesn't handle coordinated omission or you found a different way to do it?

I didn't make any coordinated omission changes (I really didn't make many changes in general), so twrk does what wrk does. It attempts to correct it after the fact by looking for requests that took twice as long as average and doing some backfilling[1].

I am no expert where coordinated omission is concerned, but my understanding is that it is most problematic in scenarios where your p90+ latency is high. Looking at the results for the 1.2M req/s test you have the following latencies:

  p50     203.00us
  p90     236.00us
  p99     265.00us
  p99.99  317.00us
  pMAX    626.00us

If you were to apply wrk's coordinated omission hack to these result, the backfilling only starts for requests that took longer than p50 x 2 (roughly) = 406us, which is probably somewhere between p99.999 and pMAX; a very, very small percentage.

I am not claiming that wrk's hack is "correct", just that I don't think coordinated omission is a major concern for *this specific workload/environment*

1. https://github.com/wg/wrk/blob/a211dd5a7050b1f9e8a9870b95513...

If I understand correctly, coordinated omission handling only matters if the benchmark is done with a fixed rate RPS right? In this case, it looks like a closed model benchmark where a fixed number of client threads just go as fast as they can.

edit: Oh, perhaps wrk2 still relies on the timer even when not specifying a fixed rate RPS.

I really like that wrk2 allows to configure fixed framerate, latency measurement works much better in this case. But wrk2 itself has bugs that doesn't allow it to use in more complicated cases, e.g. lua scripts are not working properly.

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