KIP-1224 — Adaptive append.linger.ms for the group coordinator and share coordinator

Accepted Kafka 4.2 ConsumerBroker

Introduces an adaptive mode for group.coordinator.append.linger.ms (value -1) that dynamically adjusts batch linger time toward 0ms under low load and rises to reduce latency impact under high load. The fixed 5ms default linger introduced a minimum latency floor for all group coordinator and share coordinator writes under KIP-848's new coordinator runtime, causing latency regressions for low-throughput workloads after upgrading to Kafka 4.0.

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