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This approach prevents a critical consistency issue: the destination cluster could retain partial transaction data that would never be completed since mirroring has stopped. This would leave the topic in an inconsistent state where read_committed consumers may be blocked due to incomplete transaction data. Additionally, the transaction coordinator would not be able to rollback these hanging transactions because there would be no __transaction_state metadata in the destination cluster.

Transactional Consumer Guarantees

Kafka consumers with isolation.level=read_committed determine transaction visibility using only the Last Stable Offset (LSO), which is computed from COMMIT/ABORT control markers in the log. Consumers never interact with the transaction coordinator or validate producer IDs. This separation between log-level markers (replicated) and coordinator state (not replicated) is why transactional consumers work correctly on mirrored topics without mirroring coordinator state. The LSO truncation during failover ensures all remaining transactions have mirrored markers, maintaining this guarantee.

Example Scenario

Consider this source cluster log:

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