Worked on enhancing the reliability of the delayed delivery tracking system in both the datastax/pulsar and apache/pulsar repositories, focusing on backend stability under high concurrency. Addressed critical race conditions and logic bugs in the InMemoryDelayedDeliveryTracker, which previously led to runtime exceptions during message processing. Applied Java and concurrent programming techniques to debug and resolve these issues, ensuring consistent fixes across forks through careful cherry-picking. Improved broker resilience and throughput by reducing error scenarios and strengthening test coverage. The work emphasized backend development, concurrency debugging, and cross-repository collaboration, resulting in a more robust message broker system for concurrent workloads.