KIP-480 — Sticky Partitioner

Accepted Kafka 2.4 Producer

Introduces a `StickyPartitioner` that sends multiple consecutive records without an explicit key to the same partition until the batch is sent, then rotates to a new partition. The default round-robin partitioner assigns each keyless record to a different partition, producing many small batches and higher latency even when `linger.ms=0`, because records for the same partition never accumulate.

Details