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https://issues.apache.org/jira/browse/KAFKA-7481?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16669323#comment-16669323
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Dong Lin commented on KAFKA-7481:
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[~ijuma] Regarding `I am still not sure if there's a lot of value in having two
separate upgrade states`, I think we need at least one separate upgrade state
for changes that can not be rolled back, since it seems weird not to be able to
downgrade if there is only minor version change in the Kafka. And the rational
for the second separate upgrade state is that, there are two categories of
changes that prevents downgrade, e.g. those that changes topic schema and those
that changes message format. It is common for user to be willing to pickup the
first category of change very soon, and only pickup the second category of
change much later after client library has been upgraded to reduce performance
cost in the broker.
> Consider options for safer upgrade of offset commit value schema
> ----------------------------------------------------------------
>
> Key: KAFKA-7481
> URL: https://issues.apache.org/jira/browse/KAFKA-7481
> Project: Kafka
> Issue Type: Bug
> Reporter: Jason Gustafson
> Priority: Blocker
> Fix For: 2.1.0
>
>
> KIP-211 and KIP-320 add new versions of the offset commit value schema. The
> use of the new schema version is controlled by the
> `inter.broker.protocol.version` configuration. Once the new inter-broker
> version is in use, it is not possible to downgrade since the older brokers
> will not be able to parse the new schema.
> The options at the moment are the following:
> 1. Do nothing. Users can try the new version and keep
> `inter.broker.protocol.version` locked to the old release. Downgrade will
> still be possible, but users will not be able to test new capabilities which
> depend on inter-broker protocol changes.
> 2. Instead of using `inter.broker.protocol.version`, we could use
> `message.format.version`. This would basically extend the use of this config
> to apply to all persistent formats. The advantage is that it allows users to
> upgrade the broker and begin using the new inter-broker protocol while still
> allowing downgrade. But features which depend on the persistent format could
> not be tested.
> Any other options?
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