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There are two cases: 1) we introduce a tagged field that is required for correctness, i.e. a new field that enforces correct access and without it results in incorrect coordinator behavior / data loss or 2) a non-tagged field is added. For both incompatible changes, we propose to have a version bump (already required for non-tagged fields) and add a new isBackwardCompatible field to the MetadataVersion enum so that the operator, if they decide, can downgrade with the --force option knowing that the downgrade is not backward compatible. 

For 1), we can still maintain compatibility with the proposed 3.X versions above. We have 3 versions: a) pre-915 version, b) 915 version (3.X versions above), and c) post-915 version (this would add a new tagged field without changing the record version). We can do a 2-step upgrade by upgrading all (a) brokers to (b), then upgrade them to (c). 

Public Interfaces

__consumer_offsets

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