FeatureSignals

Evaluation Engine

The evaluation engine is the core of FeatureSignals. It determines what value a feature flag returns for a given evaluation context.

Evaluation Flow

text
1. Flag exists?          → NO: NOT_FOUND
2. Flag expired?         → YES: DISABLED
3. Env state enabled?   → NO: DISABLED
4. Mutex group winner?  → NO: EXCLUDED
5. Prerequisites met?   → NO: PREREQ
6. Targeting rules      → MATCH: value
7. Default rollout      → IN: rollout
8. A/B variants         → ASSIGN variant
9. Fallthrough           → default value

Each step short-circuits — the first matching condition determines the result.

Consistent Hashing

FeatureSignals uses MurmurHash3 (x86, 32-bit) for all bucket assignments:

text
hash = MurmurHash3(flagKey + "." + userKey, seed=0)
bucket = hash % 10000   // range: 0–9999

Performance

  • Zero-allocation hot path (except rule sorting)
  • No database calls during evaluation (cache hit)
  • No network calls from SDKs during variation reads
  • O(rules + conditions) per evaluation

Next Steps