The original formulas used clamp_min(denominator, 1) to avoid divide-
by-zero, but that inflates the denominator when request rate is < 1/s.
Real example from prod: ~0.04 req/s, all successful, displayed as
1.02% health (red) instead of ~100%.
Switch to (numerator or vector(0)) / denominator:
- Missing "hit" series (no cache hits yet) → numerator resolves to 0
instead of empty set, so the stat shows 0% instead of "No data".
- Zero traffic (empty denominator) → whole expr is empty, Grafana
renders "No data", which is the correct behaviour for a health
stat when nothing's happening.
- Non-zero low traffic → ratio is true ratio, not artificially
depressed by the clamp.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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