Track · 2:30 · Liner note
The Patient Ninety-Fifth
A percentile is the value below which a given share of observations fall, so the 95th percentile of response time exposes the slow tail that an average hides.
Most requests are fast, which is why the average looks healthy while a few users wait far too long. The 95th percentile is the value that 95 percent of requests come in under, and it shows the tail the mean smooths over. The Patient Ninety-Fifth is the number that waits at the edge of the distribution until someone checks.
Report p95 or p99 for latency and delay, never just the mean. Do not average percentiles across groups, since the result is not valid; compute them from the combined data or from mergeable sketches. And state the window you calculated over.