Hi, Tomasz! Could you please set linger.ms=0 explicitly in the test harness and run the test again?
In 3.9.2, the default value of linger.ms is 0, while in 4.x it seems to be 5. Does the RTT include the two send actions from the producer? If so, I wonder whether this could also be explained by an increase of roughly linger.ms × 2. What do you think? FYI - 3.9.2 linger.ms - https://github.com/apache/kafka/blob/5e9866f43ab8e7e41ef39e5584ac50019381328d/clients/src/main/java/org/apache/kafka/clients/producer/ProducerConfig.java#L388 - trunk linger.ms - https://github.com/apache/kafka/blob/9a28bd23ad10454ba911b600d5d21e8cc023006f/clients/src/main/java/org/apache/kafka/clients/producer/ProducerConfig.java#L405 Best regards Sanghyeok An
