[KAFKA-15537] Unsafe metadata.version downgrade is not supported

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.6.0
• Fix Version/s: 3.7.0
• Component/s: documentation
• Assignee: Federico Valeri
• Reporter: Federico Valeri
• Created: 04/Oct/23 12:21
• Updated: 12/Oct/23 03:13
• Resolved: 12/Oct/23 03:13

Description

In KIP-778 we introduced the "unsafe" (lossy) downgrade in case metadata has changes in one of the versions between target and current, as defined in MetadataVersion.

The documentation says it is 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 command line tool shows that this doesn't work.

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.

This is also a mentioned in KIP-868: "Note that lossy downgrades of the metadata log are detailed in KIP-778 and not yet fully implemented as of Kafka 3.3".

Additionally, you can't do any safe downgrade, because cluster metadata records are still evolving and every release has changes.

Issue Links

• is caused by: KAFKA-13896 Support unsafe downgrades in KRaft
• links to: GitHub Pull Request #14484