Jepsen Testing

Jepsen Testing

Intake

• Identify the system under test and the exact client surface (Redis, S3, Kafka, HTTP, gRPC).
• Define what "acknowledged" means for each operation (what does the client treat as committed).
• Write the claimed consistency guarantees as a checkable property (linearizable register, RYW, monotonic reads, serializable txns).
• Specify the failure model to test (crash-stop, partitions, clock skew, disk stalls, restarts).
• Decide whether the test must be multi-surface (write via Redis, read via S3) to validate cross-frontend coherence.

Workload Design

• Prefer the smallest workload that can falsify the claim.
• Use a mix of reads and writes that creates ambiguous interleavings.
• Add a "witness" invariant that is easy to explain:
• Lost acknowledged write.
• Read sees a value that cannot be explained by any sequential execution respecting real-time order.
• List-append: element lost/duplicated or observed order implies a cycle.

Checker Selection

• Register or map semantics: use a linearizability checker.
• Transactional / multi-object semantics: use Elle-style anomaly detection (write cycles, dirty reads, lost updates).
• If linearizability is too strong for the product, explicitly select a weaker model and encode it (do not silently downgrade).

Fault (Nemesis) Selection

• Partitions: majority/minority splits, bridge partitions, flapping partitions.
• Process faults: kill and restart, node reboot, rolling restarts.
• Time faults: clock offsets and jumps if the system relies on time.
• Storage faults: fsync latency, I/O stalls, disk-full behavior (only if safe and reversible).

Run and Minimize

• Start with a short, low-concurrency run until the harness is stable.
• When a failure appears, minimize by reducing:
• Keys, operation count, and concurrency.
• Fault intensity and schedule complexity.
• Preserve determinism (fixed seeds, fixed partition schedule) so a failing history can be reproduced.

Reporting

• State the exact claim under test and the precise pass/fail property.
• Include the workload, nemesis schedule, and a minimal failing history excerpt.
• Distinguish availability failures (timeouts) from safety failures (incorrect ok results).