Property Based Testing Confluent Cloud Storage for Fun and Safety

Confluent employs property-based testing to ensure the reliability and efficiency of Confluent Cloud's Tiered Storage feature, which optimizes storage costs and elasticity by transferring data from costly local disks to scalable object storage. This testing strategy complements traditional methods like example-based and integration testing, focusing on critical behaviors such as preventing premature data deletion and ensuring correct data exposure and tiering. The process involves using ScalaCheck’s stateful testing to validate the log-oriented storage system's retention logic, with initial and action generators creating varied test scenarios. Actions like appending records, advancing high watermarks, and simulating segment uploads are tested to ensure the system's integrity and performance. Findings from these tests have led to improved understanding and identification of issues like non-idempotent retention and high watermark mishandling, prompting further enhancements. Future efforts will focus on implementing additional features like retention.bytes and automatic segment rolls to expand the scope of property testing.