A percentage rollout should give one user a stable experience without storing an assignment for every account. A deterministic hash can place each user in a reproducible bucket that every application server calculates independently.
Design a FeatureFlagBucketer class:
FeatureFlagBucketer() creates a stateless bucketer.int bucket(String userId) returns the user's stable bucket from 0 through 99.boolean isEnabled(String userId, int rolloutPercent) returns whether the feature is enabled for that user.
Use this exact unsigned 32-bit polynomial hash:
The bucket is h % 100. A user is enabled exactly when:
Do not use a language's built-in string hash. Each call is independent and must produce the same result on every supported language.
Example 1:
Input:
Output:
Explanation: The users land in buckets 40, 17, 9, and 76. At a 50% rollout, only buckets below 50 are enabled.
Example 2:
Input:
Output:
Explanation: Hashing is deterministic, so these IDs always return the same three buckets without stored assignments.
Constraints
1 <= userId.length <= 40userId contains printable ASCII characters.0 <= rolloutPercent <= 100- Use the specified unsigned 32-bit polynomial hash.
- At most
200 total method calls are made.
Build Sticky Feature-Flag Bucketseasy