Load Testing · Senior · Question 23 of 76
How do you get correct fleet-wide p99 from server-side histograms?
- 1Sum histogram buckets across instances, then compute the quantile
- 2Average the p99 values of all instances on the dashboard
- 3Take the p99 from the busiest instance and assume it's global
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Correct answer: Sum histogram buckets across instances, then compute the quantile
Explanation
Percentiles can't be averaged. Bucketed histograms can be summed, e.g. histogram_quantile(0.99, sum by (le) (rate(...))) in Prometheus.