universal-scalability-law
Installation
SKILL.md
Universal Scalability Law
The model
Adding workers helps, then stops helping, then starts hurting. Neil Gunther's USL puts a number on where each of those turns happens. Relative throughput at N workers:
C(N) = N / (1 + α(N-1) + βN(N-1))
| Term | Name | Cause |
|---|---|---|
| α | Contention | Serialized work: locks, single-threaded sections, a shared queue |
| β | Coherency | Cross-talk: every worker must agree with every other one |
Setting β = 0 gives Amdahl's law: throughput approaches a ceiling of 1/α and stays there.
With β > 0 the curve does not plateau. It peaks and then declines. Adding capacity past the peak makes the system slower. That is the result worth knowing, and it is why "just add more servers" sometimes makes an incident worse.