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https://issues.apache.org/jira/browse/KAFKA-6774?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16459266#comment-16459266
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Jason Gustafson commented on KAFKA-6774:
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[~vahid] The suggestion here would be to have the standalone consumer skip
querying for committed offsets if no groupId is provided. So if the user hasn't
done in explicit seek, then we would try to use the auto reset behavior. Does
that seem reasonable?
> Improve default groupId behavior in consumer
> --------------------------------------------
>
> Key: KAFKA-6774
> URL: https://issues.apache.org/jira/browse/KAFKA-6774
> Project: Kafka
> Issue Type: Improvement
> Components: consumer
> Reporter: Jason Gustafson
> Assignee: Vahid Hashemian
> Priority: Major
> Labels: needs-kip
>
> At the moment, the default groupId in the consumer is "". If you try to use
> this to subscribe() to a topic, the broker will reject the group as invalid.
> On the other hand, if you use it with assign(), then the user will be able to
> fetch and commit offsets using the empty groupId. Probably 99% of the time,
> this is not what the user expects. Instead you would probably expect that if
> no groupId is provided, then no committed offsets will be fetched at all and
> we'll just use the auto reset behavior if we don't have a current position.
> Here are two potential solutions (both requiring a KIP):
> 1. Change the default to null. We will preserve the current behavior for
> subscribe(). When using assign(), we will not bother fetching committed
> offsets for the null groupId, and any attempt to commit offsets will raise an
> error. The user can still use the empty groupId, but they have to specify it
> explicitly.
> 2. Keep the current default, but change the consumer to treat this value as
> if it were null as described in option 1. The argument for this behavior is
> that using the empty groupId to commit offsets is inherently a dangerous
> practice and should not be permitted. We'd have to convince ourselves that
> we're fine not needing to allow the empty groupId for backwards compatibility
> though.
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