April 2026 monthly summary for apache/hadoop focusing on business value and technical achievements. No new user-facing features were delivered this month; the primary emphasis was on stability and reliability improvements within the Hadoop YARN resource manager. A critical concurrency bug affecting node attribute updates was fixed, improving thread-safety and preventing instability under concurrent scheduling. Key fix: - Resource Manager Node Attributes Update Concurrency Bug (YARN-11942): Resolved a ConcurrentModificationException in NodeAttributesManagerImpl by adjusting how node attributes are updated, ensuring thread-safety in the resource manager. Impact and outcomes: - Increased stability and reliability of the Resource Manager under high-concurrency workloads, reducing the risk of outages in multi-tenant environments. - Improved correctness of node attribute state propagation to the scheduler, leading to more predictable resource allocation. - Strengthened the foundation for future features that rely on node attribute data without introducing race conditions. Technologies/skills demonstrated: - Java concurrency patterns and thread-safety hardening in a complex, large-scale data-processing framework - Code review and collaborative development workflow (commit referenced below) - YARN internals knowledge and system-wide reliability improvements