KIP-250 — Add Support for Quorum-based Producer Acknowledgment

Discussion ProducerBroker

Adds a `acks=quorum` producer acknowledgment mode that waits for a configurable quorum (e.g., majority) of in-sync replicas to acknowledge rather than all ISRs, reducing tail latency caused by the slowest ISR member. With `acks=all`, produce P999 latency spikes to `replica.lag.time.max.ms` (often 10s) because a lagging-but-still-in-ISR follower determines the worst-case latency.

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