Result with flush | Method | Mean | Error | StdDev | Allocated | |------------------- |---------:|---------:|---------:|----------:| | KafkaProducerSync | 15.90 ms | 0.216 ms | 0.192 ms | 6.32 KB | | KafkaProducerAsync | 15.55 ms | 0.214 ms | 0.200 ms | 6.77 KB |

Not fair test, because during async you are awaiting delivery result, but with sync not (actually fire and forget). Call flush after sync produce to await callback get called