The scenario
Replace modulo sharding with a hash ring so a joining node moves few keys, not all of them.
A failure to reason about
Adding one worker changes the routing of far more keys than the operator expects, producing an avoidable rebalance.
Illustrative context for the topic. The exercise’s full requirements arrive in the workspace.
Questions to bring to your review
- Which caller makes the reported behavior visible?
- What focused regression would distinguish the current behavior from the requirement?
- What existing behavior must remain intact after the change?
Skills you will practice
- Consistent hashing
- Sharding
- Rebalancing
Read the existing code, reproduce the reported behavior, review proposed changes, and verify your final implementation. You can use AI assistance while staying responsible for the result.
Prepare with a worked example
- How to review AI-generated code
A worked review of a cache patch: establish the contract, find a counterexample, verify the fix, and explain the evidence.
See how nrml evaluates an attempt, including the limits of automated evidence.