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https://issues.apache.org/jira/browse/KAFKA-7174?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17107880#comment-17107880
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Sophie Blee-Goldman commented on KAFKA-7174:
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Technically w.r.t version probing we still just detect the case by comparing
the version numbers rather than encoding the followup rebalance in the
subscription. I considered changing this during
[pull/8596|https://github.com/apache/kafka/pull/8596] but ultimately decided to
leave this logic as is, since we need to process the version number anyway in
order to detect that we need to downgrade.
I might be missing the real point of this ticket, but, I think we should close
it as Not a Problem?
> Improve version probing of subscription info
> --------------------------------------------
>
> Key: KAFKA-7174
> URL: https://issues.apache.org/jira/browse/KAFKA-7174
> Project: Kafka
> Issue Type: Improvement
> Components: streams
> Reporter: Ted Yu
> Priority: Major
> Labels: compatibility
>
> During code review for KAFKA-5037, [~guozhang] made the following suggestion:
> Currently the version probing works as the following:
> when leader receives the subscription info encoded with a higher version that
> it can understand (e.g. the leader is on version 3, while one of the
> subscription received is encode with version 4), it will send back an empty
> assignment with the assignment encoded with version 3, and also
> latestSupportedVersion set to 3.
> when the member receives the assignment, it checks if latestSupportedVersion
> is smaller than the version it used for encoding the sent subscription (i.e.
> the above logic). If it is smaller, then it means that leader cannot
> understand, in this case, version 4. It will then set the flag and then
> re-subscribe but with a down-graded encoding format of version 3.
> NOW with PR #5322, we can let leader to clearly communicate this error via
> the error code, and upon receiving the assignment, if the error code is
> VERSION_PROBING, then the member can immediately know what happens, and hence
> can simplify the above logic.
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