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https://issues.apache.org/jira/browse/KAFKA-20090?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18056062#comment-18056062
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Justine Olshan commented on KAFKA-20090:
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Hey [~chickenchickenlove]
Thanks, I think one of the paths we were considering is always triggering the
generate producer ID logic on max epoch - 1 (right now we only do this in the
non-fencing case).
I think this is similar if not the same as your suggestion. I know that
[~alivshits] may have some thoughts as well with the exact logic he was
thinking.
We also may need to consider the non overflow scenarios and how those can be
handled. (Do we want to return to the double epoch bump?)
> TV2 can allow for ongoing transactions with max epoch that never complete
> -------------------------------------------------------------------------
>
> Key: KAFKA-20090
> URL: https://issues.apache.org/jira/browse/KAFKA-20090
> Project: Kafka
> Issue Type: Task
> Reporter: Justine Olshan
> Assignee: sanghyeok An
> Priority: Major
>
> When transaction version 2 was introduced, epoch bumps happen on every
> transaction.
> The original EndTransaction logic considers retries and because of epoch
> bumps we wanted to be careful to not fence ourselves. This means that for
> EndTransaction retries, we have to check if the epoch has been bumped to
> consider a retry.
> The original logic returns the current producer ID and epoch in the
> transaction metadata when a retry has been identified. The normal end
> transaction case with max epoch - 1 was considered and accounted for – the
> state there is safe to return to the producer.
> However, we didn't consider that in the case of fencing epoch bumps with max
> epoch - 1, where we also bump the epoch, but don't create a new producer ID
> and epoch. In this scenario the producer was expected to be fenced and call
> init producer ID, so this isn't a problem, but it is a problem if we try to
> return it to the producer.
> There is a scenario we race a timeout and end transaction abort with max
> epoch - 1, we can consider the end transaction request a "retry" and return
> max epoch as the current producer's epoch instead of fencing.
> 1. The fencing abort on transactional timeout bumps the epoch to max
> 2. The EndTxn request with max epoch - 1 is considered a "retry" and we
> return max epoch
> 3. The producer can start a transaction since we don't check epochs on
> starting transactions
> 4. We cannot commit this transaction with TV2 and we cannot timeout the
> transaction. It is stuck in Ongoing forever.
> I modified
> [https://github.com/apache/kafka/blob/aad33e4e41aaa94b06f10a5be0094b717b98900f/core/src/test/scala/unit/kafka/coordinator/transaction/TransactionCoordinatorTest.scala#L1329]
> to capture this behavior. I added the following code to the end:
> {code:java}
> // Transition to COMPLETE_ABORT since we can't do it via writing markers
> response callback
> txnMetadata.completeTransitionTo(new
> TxnTransitMetadata(txnMetadata.producerId(), txnMetadata.prevProducerId(),
> txnMetadata.nextProducerId(), Short.MaxValue, Short.MaxValue -1,
> txnTimeoutMs, txnMetadata.pendingState().get(), new
> util.HashSet[TopicPartition](), txnMetadata.txnLastUpdateTimestamp(),
> txnMetadata.txnLastUpdateTimestamp(), TV_2))
> coordinator.handleEndTransaction(transactionalId, producerId,
> epochAtMaxBoundary, TransactionResult.ABORT, TV_2, endTxnCallback)
> assertEquals(10, newProducerId) assertEquals(Short.MaxValue, newEpoch)
> assertEquals(Errors.NONE, error){code}
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