The default fetch.min.bytes is 1, that's true, but the default fetch.max.bytes is 50 MiB. And fetching small amounts of data repeatedly doesn't impose much ove

The default fetch.min.bytes is 1, that's true, but the default fetch.max.bytes is 50 MiB. And fetching small amounts of data repeatedly doesn't impose much overhead unless you're deliberately disconnecting and reconnecting between polls. And I assure you, you can definitely bottleneck network before CPU and/or network threads, Kafka was literally designed for very large numbers of consumers. And as for tuning, Kafka The Definitive Guide is pretty much as the name suggests. I've been recommending it very strongly, especially the chapters on monitoring and cluster replication, for years. You can download a free draft copy of the 2nd edition from Confluent, check it out :)