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Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

KAFKA-3853 asks for an improvement to the new-consumer option of the consumer group command. This command, when passed a consumer group that has no consumer (i.e., when the group state is Empty), currently reports an error indicating that there is no active member:

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When the group is Stable (i.e. when there are active consumers in the group), the offsets associated with the group are returned as part of the info returned for each consumer in the group in terms of a ConsumerSummary record. But there is no ConsumerSummary record if there is no consumer in the group, and therefore, in that scenario a different method is required for extracting those offsets.

Public Interfaces

This is the current schema for DescribeGroups (version 0).

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There should be no impact to existing users of this protocol. The Request schema remains unchanged, and the Response schema is only expanded. There is no change in the existing Response structure, and, therefore, users who use version 0 of the schema should not be affected. The code behind kafka-consumer-groups.sh will also be updated (as requested in the JIRA) to return more helpful information. In case it is necessary to provide the old output as well, a new parameter can be defined for the tool to report the new information; while the old way of running the tool still prints out the old output.

Rejected Alternatives

If there are alternative ways of accomplishing the same thing, what were they? The purpose of this section is to motivate why the design is the way it is and not some other way.