> A popular way to do it wrong is to use summary statistics that regularly emit a quantile, for example don't collect the p90 from every server every minute. Th

> A popular way to do it wrong is to use summary statistics that regularly emit a quantile, for example don't collect the p90 from every server every minute. That discards far too much information. Instead, collect the CDF of service times. CDFs can be combined in a lossless way, and they carry their own denominators. Basically if you are using the typical Prometheus setup, you should be getting the right data. And choose the right quantization for histograms/cdfs. > To go to the next level I would suggest also emitting the sum and sum of squares, which will make your summary statistic far more useful. Histograms should also give you the sum. I haven't seen sum of squares in many monitoring setups; is this for underlying metrics that are differences/errors?