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https://issues.apache.org/jira/browse/KAFKA-15537?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17771844#comment-17771844
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Federico Valeri commented on KAFKA-15537:
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Sure. I already opened a PR to fix the documentation and improve the error
message.
https://github.com/apache/kafka/pull/14484
> Unsafe metadata.version downgrade is not supported
> --------------------------------------------------
>
> Key: KAFKA-15537
> URL: https://issues.apache.org/jira/browse/KAFKA-15537
> Project: Kafka
> Issue Type: Bug
> Reporter: Federico Valeri
> Priority: Major
>
> In KIP-778 we introduced the "unsafe" downgrade in case one of the metadata
> versions between target and current have changes, as defined in
> MetadataVersion.
> This is a lossy downgrade where each node rebuilds its metadata snapshots,
> omitting the metadata changes.
> Currently, this is not supported, as shown by the following command.
> {code}
> bin/kafka-features.sh --bootstrap-server :9092 downgrade --metadata 3.4
> --unsafe
> Could not downgrade metadata.version to 8. Invalid metadata.version 8.
> Unsafe metadata downgrade is not supported in this version.
> 1 out of 1 operation(s) failed.
> {code}
> Also note that documentation says it's possible:
> "Note that the cluster metadata version cannot be downgraded to a
> pre-production 3.0.x, 3.1.x, or 3.2.x version once it has been upgraded.
> However, it is possible to downgrade to production versions such as 3.3-IV0,
> 3.3-IV1, etc."
> The error message could be improved: "Unsafe metadata downgrade is not
> supported in this Kafka version."
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