Default Acknowledgement Mode for Share Groups

[sandonjacobs]

What was the design process for using EXPLICIT acknowledgement mode as the default in Spring-Kafka? I ask because the default for Apache Kafka is IMPLICIT.

[sobychacko]

@sandonjacobs See this PR for some reasoning on that decision: #4376

See this docs section also: https://docs.spring.io/spring-kafka/reference/kafka/kafka-queues.html#share-ack-mode-explicit

The short version is that in EXPLICIT mode, the listener container takes full control over ack decisions without the listener (user) code involvement. This is similar to how Spring Kafka disables auto.commit in regular consumer container and let the container handles all commit decisions. Users can opt-into the default Kafka behavior in both cases if need be.