KAFKA-20739: Transaction coordinator accepts InitProducerId v6 keepPreparedTxn recovery#22704
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| // transaction exists, preserve it and return its producer id/epoch so the client can | ||
| // finalize it. There is no state change, so respond directly without a log append. | ||
| val preservedResult = coordinatorEpochAndMetadata.toOption.flatMap { existingEpochAndMetadata => | ||
| val txnMetadata = existingEpochAndMetadata.transactionMetadata |
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The epoch fence is skipped on the preserve path —
the prepared txn's epoch must stay valid for completeTransaction.
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Ref https://issues.apache.org/jira/browse/KAFKA-20739
The transaction coordinator rejected every InitProducerId keepPreparedTxn=true with UNSUPPORTED_VERSION (a stub), so a 2PC producer could not recover a prepared transaction after a crash/restart.
TransactionCoordinator.handleInitProducerId: replace the stub — reject only keepPreparedTxn && !enable2Pc (INVALID_REQUEST); otherwise proceed.
Add a recovery short-circuit: when an ongoing 2PC transaction exists (ONGOING + isDistributedTwoPhaseCommitTxn), preserve it and return its producerId/epoch as ongoingTxnProducerId/ongoingTxnProducerEpoch
KafkaApis.createResponse: populate the v6 ongoing response fields.
Client side already sends v6 (KAFKA-20738) and consumes these response fields (TransactionManager → PREPARED_TRANSACTION), so the two complete the recovery loop together.
Tests: TransactionCoordinatorTest — keepPreparedTxn without 2PC → INVALID_REQUEST; with 2PC + no ongoing txn → NONE; with an ongoing 2PC txn → returns its pid/epoch and asserts no log append.