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In the current consumer protocol, the field `member.id` is assigned by broker to track group member status. A new consumer joins the group with `member.id` field set as UNKNOWN_MEMBER_ID (empty string), since it needs to receive the identity assignment from broker first. For request with unknown member id, Broker broker will blindly accept the new join group request, store the member metadata and return a UUID to consumer. The edge case is that if initial join group request fails, or the consumer keeps restarting, there will be many leftover MemberMetadata within group metadata cache which will eventually burst broker memory. The detection and fencing of invalid join group request is crucial for broker stability.

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MEMBER_ID_REQUIRED(79, "Consumer needs to have a valid member id before actually joiningentering group ", MemeberIdRequiredException::new),

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