Hi all, I'd like to propose PIP-474: Key_Shared Hot Key Overflow Mechanism.
Key_Shared is Pulsar's only built-in solution for parallel consumption with per-key ordering. But it has a critical production issue: a single stuck consumer can starve ALL other keys across ALL partitions within minutes, due to the containsStickyKeyHash ordering check flooding the Replay queue. This becomes especially urgent as AI inference workloads adopt MQ as their transport layer — slow consumption (seconds per request) plus strict per-key ordering is exactly what Key_Shared is designed for, yet the hot-key starvation bug makes it unusable in production. PIP-474 proposes diverting hot-key messages to an independent Overflow ManagedLedger, unblocking Normal Read and mark-delete advancement while preserving at-least-once delivery and per-key ordering. Zero overhead when no hot keys are present. PIP: https://github.com/apache/pulsar/pull/25706 Feedback welcome. Thanks, Xiangying Meng
