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For applications writing to external systems (Databases, S3) that require transactional acknowledgments coordinated with their own internal checkpoints.

• Tool: KIP-1302 1310 General Transaction Session

• The Flow: Aggregates acks and commits them via a background transaction once the external sink confirms the write.

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Abort case: 

6. Corner Cases

Failure Scenarios

• Crash Before/During Txn: If the application crashes before commitTransaction(), the Transaction Coordinator (TC) auto-aborts

• The "Critical Case" (Crash after sendShareAcks): If a crash occurs after acks are sent but before the final commit, the TC sends Abort  signal and ensures pending acks are discarded.

• Zombie Producers: If a new producer instance starts, the old one is fenced. Any in-flight output or acks are discarded by the TC, preventing "split-brain" duplicates.

• Post-Prepare Crash: If the TC crashes after logging PREPARE_COMMIT, the 2PC protocol ensures that the transaction is finalized upon recovery. Both outputs and acks will successfully materialize.

7. Compatibility, Deprecation, and Migration Plan

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