FA-73052 / Probabilistic sketches / Member archive

Count-Min sketch with conservative update: zero and negative counts accepted · case 02

Deletions are acknowledged although conservative cells cannot decrease, and the stream total drifts.

Member previewVariant 2 · 3 implementations · 6 checks per implementation

Case contract

Input {w, d, ops}. Row r hashes key to ((A_r*key + B_r) mod 2^31-1) mod w with fixed A and B. add with count <= 0 is "rejected" (conservative update cannot represent deletions). Otherwise the current estimate e is the minimum of the key's cells, and each cell is raised to max(cell, e + count). The stream total counts accepted mass and the overestimate bound is ceil(e/w * total). q returns the minimum of the key's cells. Return [results, total, bound, table].

Why this case matters

Conservative update reduces Count-Min overestimation in heavy-hitter monitors, but only if the raise-to-target rule is applied exactly.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
zero and negative counts	`[["ok", "ok", "ok", 5], 3, 2, [[0, 0, 0, 5, 0, 0, 0], [0, 0, 0, 5, 0, 0, 0]]]`	`[["rejected", "rejected", "ok", 5], 5, 2, [[0, 0, 0, 5, 0, 0, 0], [0, 0, 0, 5, 0, 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.