FA-73417 / Rate limiter algorithms / Member archive

Fixed-window request counter: one counter shared by every key · case 02

One tenant exhausts the quota for everyone.

Member previewVariant 2 · 3 implementations · 6 checks per implementation

Case contract

Input {limit, window_ms, requests [[t, key]]}. Windows are epoch-aligned: index t div W. Each (case-sensitive) key keeps [window, count]; a request in a later window resets the count, while a late request from an earlier window is charged to the current window. Allow while count < limit and report remaining = limit - count after charging; denials are not counted. reset = ms until the end of the key's current window. Return [[decision, remaining, reset]].

Why this case matters

Fixed windows are the simplest API quota; alignment, reset and key-identity mistakes show up as double bursts, stuck quotas or cross-tenant throttling.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
keys are isolated and case-sensitive	`[["allow", 0, 490], ["deny", 0, 480], ["deny", 0, 470], ["deny", 0, 458]]`	`[["allow", 0, 490], ["allow", 0, 480], ["allow", 0, 470], ["deny", 0, 458]]`	Failed

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