FA-73765 / Rate limiter algorithms / Member archive

EWMA arrival-rate throttle: decay constant treated as seconds · case 05

The estimate barely reacts to new arrivals and throttling kicks in minutes late.

Member previewVariant 5 · 3 implementations · 6 checks per implementation

Case contract

Input {tau_ms, limit_rps, requests [t_ms]}. The rate estimate r starts at 0. For each arrival strictly after the latest seen time, dt = t - last, a = exp(-dt/tau) and r = a*r + (1-a)*(1000/dt) requests per second. Simultaneous or late arrivals leave r unchanged and never move the clock backwards. Every arrival reports deny if r > limit else allow, with r rounded to 3 decimals.

Why this case matters

Irregular-interval EWMA estimators throttle clients by smoothed request rate; time-unit and duplicate-timestamp handling decide whether bursts are detected.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
steady ten per second	`[["allow", 0.0], ["allow", 0.001], ["allow", 0.002], ["allow", 0.003], ["allow", 0.004], ["allow", 0.005], ["allow", 0.006], ["allow", 0.007], ["allow", 0.008], ["allow", 0.009]]`	`[["allow", 0.0], ["allow", 0.952], ["allow", 1.813], ["allow", 2.592], ["allow", 3.297], ["allow", 3.935], ["allow", 4.512], ["allow", 5.034], ["allow", 5.507], ["allow", 5.934]]`	Failed

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