Yufeng Zhu focused on improving the stability and correctness of DDL extension samples in the apache/calcite repository during April 2025. He addressed a misconfiguration that prevented these samples from running by updating the parserFactory to use ServerDdlExecutor, resolving a longstanding issue and restoring the functionality of official documentation examples. His work emphasized build configuration and documentation quality, ensuring that onboarding for new users and contributors became smoother. Using Java and Gradle, Yufeng demonstrated a strong understanding of Calcite’s DDL extension pipeline, prioritizing code maintainability and reliability over new feature development during this period. The work was targeted and impactful.