FA-73783 / Rate limiter algorithms / Member archive

EWMA arrival-rate throttle: late arrival rewinds the clock · case 03

After a late arrival the next interval is measured from the past and appears artificially long or short.

Member previewVariant 3 · 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
late arrival ignored for clock	`[["allow", 0.0], ["allow", 0.787], ["allow", 0.787], ["allow", 1.354], ["allow", 2.015]]`	`[["allow", 0.0], ["allow", 0.787], ["allow", 0.787], ["allow", 1.551], ["allow", 2.176]]`	Failed

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