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Comment by na-- | Hacker News Reader

That's one of the main uses, yes. Although k6 gives you a lot of flexibility to decide what your pass/fail criteria are with its custom metrics ( https://k6.io/docs/using-k6/metrics#custom-metrics ), checks (https://k6.io/docs/using-k6/checks) and thresholds ( https://k6.io/docs/using-k6/thresholds ).

See the example in https://github.com/loadimpact/k6/#checks-and-thresholds. If, at the end of the test run, some of these rules (encoded as `thresholds`) were unsatisfied, k6 will exit with a non-zero exit code (and thus fail your CI check): - The 95th percentile of all HTTP request durations should be be less than 500ms - The 99th percentile of all HTTP request durations that were tagged with `staticAsset:yes` should be less than 250ms - The failure rate of the checks should be less than 1%, although if it's more than 5% the test will abort immediately.

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Does K6 deal with the coordinated omission problem?

Gil Tene (Azul Systems) has argued convincingly [1] (slides [2]) that monitoring tools get latency measurement wrong because sudden spikes aren't represented correctly in timings because of averaging and the wrong use of percentiles.

He argues that percentiles simply aren't useful, because, statistically, most requests will experience >= 99.99-percentile response times. All percentiles lie; the only truly useful and realistic number is, in fact, the 100th percentile.

He also argues that the most revealing way to show latency is with a complete histogram.

I haven't used K6 yet, but I've been looking for a good load-testing tool, and intend to try it out.

[1] https://www.youtube.com/watch?v=lJ8ydIuPFeU

[2] https://www.azul.com/files/HowNotToMeasureLatency_LLSummit_N...

This used to be an issue with older k6 versions, but since v0.27.0 we have arrival-rate executors [1] that should address the biggest issue of coordinated omission. And we've always measured the max value of all metrics, even when they are not exported to some external output and we just show the end-of-test summary.

It has been a while since I watched these Gil Tene talks, so I might be missing something, but I think the only remaining task we have is to adopt something like his HDR histogram library [2]. And that's mostly for performance reasons, though we'll probably play around with the correction logic as well.

[1] https://k6.io/docs/using-k6/scenarios/arrival-rate

[2] https://github.com/loadimpact/k6/issues/763

That's perfect, thanks!

That's an interesting talk.

k6 allows the user to choose[1] which metrics are relevant for the particular test. By default, it displays max or p(100), p(95), p(90), min, med, and avg. User can specify other values such as p(99.995)

It's also possible to create completely custom metrics[2] to track whatever is relevant to the user.

k6 allows the user to change almost all aspects of execution, tracking, and reporting.

[1] https://k6.io/docs/using-k6/options#summary-trend-stats

[2] https://k6.io/docs/using-k6/metrics

Yup. I put a couple of metrics for failures of a couple of types in the load script and ship them out to InfluxDb/Grafana for plotting in the very first graph. That way, if I see a lot of "failure" color, flags go up. Otherwise the usual amount of background noise is ok.

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