FA-73399 / Rate limiter algorithms / Member archive

Generic cell rate algorithm limiter: oversize check compares units with time · case 04

Requests larger than the burst receive retry hints that can never succeed.

Member previewVariant 4 · 3 implementations · 6 checks per implementation

Case contract

Input {period_ms T, burst B, requests [[t, quantity]]}. State TAT starts at 0. A quantity above B is ["never", 0, 0]. Otherwise tat = max(TAT, t) and new_tat = tat + q*T; the request is allowed iff new_tat - t <= B*T, in which case TAT = new_tat and remaining = floor((B*T - (TAT - t))/T). A denied request leaves TAT unchanged and reports retry_after = new_tat - B*T - t and remaining floor((B*T - (tat - t))/T). Return [[decision, retry_after, remaining]].

Why this case matters

GCRA limiters store a single theoretical-arrival timestamp per key; every decision and header value is derived from it, so small formula errors leak bursts or starve clients.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
multi-unit request	`[["allow", 0, 1], ["deny", 20, 1], ["allow", 0, 1], ["deny", 100, 0]]`	`[["allow", 0, 1], ["deny", 20, 1], ["allow", 0, 1], ["never", 0, 0]]`	Failed

MEMBER ARCHIVE

The complete case is available to members.

This record includes three runnable implementations, regression fixtures, execution results, and source hashes.

Member access is invitation-based. Sign in with your invited account to inspect the sources.