| |
| from prometheus_client import Gauge |
| import math |
|
|
|
|
| LOWER_BOUND = Gauge( |
| "arf_rust_agreement_lower_bound", |
| "Lower 99.9% Wilson bound on agreement rate", |
| ) |
|
|
|
|
| def wilson_lower(success, total, z=3.291): |
| """ |
| Compute the lower bound of the Wilson confidence interval |
| for a binomial proportion. |
| |
| Parameters |
| ---------- |
| success : int |
| Number of agreed evaluations. |
| total : int |
| Total number of shadow evaluations (agreed + diverged). |
| z : float |
| Z‑score for the desired confidence level (default 3.291 for 99.9%). |
| |
| Returns |
| ------- |
| float |
| Lower bound of the Wilson interval, clamped to [0, 1]. |
| """ |
| if total == 0: |
| return 0.0 |
| p = success / total |
| n = total |
| denom = 1 + z**2 / n |
| center = (p + z**2 / (2 * n)) / denom |
| margin = z * math.sqrt(p * (1 - p) / n + z**2 / (4 * n**2)) / denom |
| return max(0.0, center - margin) |
|
|
|
|
| def update(agreed, diverged): |
| """ |
| Query the Prometheus agreement counters and set the lower‑bound gauge. |
| |
| This function is called periodically by the background thread started |
| in the API lifespan (see `app/main.py`). |
| |
| Parameters |
| ---------- |
| agreed : int |
| Current value of `arf_rust_agreement_total{result="agreed"}`. |
| diverged : int |
| Current value of `arf_rust_agreement_total{result="diverged"}`. |
| """ |
| lower = wilson_lower(agreed, agreed + diverged) |
| LOWER_BOUND.set(lower) |
|
|
