tail-latency
Installation
SKILL.md
Tail latency
One slow server sets the latency of every request that touches it. At a fan-out of 100, a single server's p99 becomes the whole system's p63.
From Dean and Barroso, The Tail at Scale (CACM 2013).
Amplification math
When a request fans out to n servers and needs all of them, the slowest determines latency. Probability that at least one hits its p99:
1 - (1 - p)ⁿ
| Servers touched | Chance of a p99 event | Chance of a p99.9 event |
|---|---|---|
| 1 | 1% | 0.1% |
| 10 | 9.6% | 1% |
| 50 | 39% | 4.9% |
| 100 | 63% | 9.5% |
| 500 | 99.3% | 39% |