Tail Latency

Symptom → diagnosis → action playbook; three analytical lenses (Little's Law, utilisation curve, percentile arithmetic); capacity planning workflow; antipatterns (sizing for average, running at high utilisation, unbounded queues); when performance tuning doesn't apply

Little's Law (L=λW), utilisation curves (W=S/(1−ρ)) and hyperbolic response-time growth, tail latency amplification in fan-out designs, percentile arithmetic (averages lie; can't average percentiles; t-digest/HdrHistogram), queues in series, thread pools as queueing systems; practical heuristics for capacity and tuning