[Question] What is the definition of GenerationID

[chientranthien]

There is a function of ConsumerGroupSession called GenerationID

• What is the definition of GenerationID?
• Is it true that GenerationID of a consumer group always increases each consumer-group rebalancing?

[dnwe]

@chientranthien yes, this is sort of exposing the internals of Kafka, but the ConsumerGroup has an ID integer that increases whenever a rebalance or change of membership occurs in the group, so that the server-side group coordinator can be sure that all members of the group are aware of the configuration/memberships and it can ignore any requests that come in referring to an old/outdated generation, forcing consumers to correctly re-join the group at the new generation

https://github.com/apache/kafka/blob/60e845626d8a465a8cfe68bb2d7d4b88d622634e/core/src/main/scala/kafka/coordinator/group/GroupMetadata.scala#L583-L598

You might find https://chrzaszcz.dev/2019/06/kafka-rebalancing/ some useful background reading as well