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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (KAFKA-6119) Silent Data Loss in Kafka011 Transactional Producer
Date Thu, 26 Oct 2017 01:08:00 GMT

    [ https://issues.apache.org/jira/browse/KAFKA-6119?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16219806#comment-16219806

ASF GitHub Bot commented on KAFKA-6119:

GitHub user apurvam opened a pull request:


    KAFKA-6119: Bump epoch when expiring transactions in the TransactionCoordinator

    A description of the problem is in the JIRA. I have added an integration test which reproduces
the original scenario, and also added unit test cases.

You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/apurvam/kafka KAFKA-6119-bump-epoch-when-expiring-transactions

Alternatively you can review and apply these changes as the patch at:


To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #4137
commit 4405e4f9c30e82864417fdbafe3817ee4acee661
Author: Apurva Mehta <apurva@confluent.io>
Date:   2017-10-26T00:58:44Z

    Bump the epoch when we abort a transaction on the coordinator

commit 9945b4f8315dc8c82aaeb003c07458a6231ee96c
Author: Apurva Mehta <apurva@confluent.io>
Date:   2017-10-26T01:06:04Z

    Lock the transaction metadata before fencing the epoch. Make the case matching exhaustive


> Silent Data Loss in Kafka011 Transactional Producer
> ---------------------------------------------------
>                 Key: KAFKA-6119
>                 URL: https://issues.apache.org/jira/browse/KAFKA-6119
>             Project: Kafka
>          Issue Type: Bug
>          Components: core, producer 
>    Affects Versions:,
>         Environment: openjdk version "1.8.0_144"
> OpenJDK Runtime Environment (Zulu (build 1.8.0_144-b01)
> OpenJDK 64-Bit Server VM (Zulu (build 25.144-b01, mixed mode)
>            Reporter: Gary Y.
>            Assignee: Apurva Mehta
>            Priority: Blocker
>              Labels: reliability
>             Fix For: 1.0.0,
> Kafka can lose data published by a transactional {{KafkaProducer}} under some circumstances,
i.e., data that should be committed atomically may not be fully visible from a consumer with
{{read_committed}} isolation level.
> *Steps to reproduce:*
> # Set {{transaction.timeout.ms}} to a low value such as {{100}}
> # Publish two messages in one transaction to different partitions of a topic with a sufficiently
long time in-between the messages (e.g., 70 s).
> # Only the second message is visible with {{read_committed}} isolation level.
> See 
> https://github.com/GJL/kafka011-transactional-producer-bug-demo/blob/master/src/main/java/com/garyyao/App.java
for a full example. Detailed instructions can be found in the {{README.md}}: https://github.com/GJL/kafka011-transactional-producer-bug-demo
> *Why is this possible?*
> Because the transaction timeout is set to a low value, the transaction will be rolled
back quickly after the first message is sent. Indeed, in the broker the following logs could
be found:
> {code}
> [2017-10-25 22:54:58,224] INFO [Transaction Coordinator 0]: Initialized transactionalId
test-producer-1508964897483 with producerId 5 and producer epoch 0 on partition __transaction_state-10
> [2017-10-25 22:55:24,260] INFO [Transaction Coordinator 0]: Completed rollback ongoing
transaction of transactionalId: test-producer-1508964897483 due to timeout (kafka.coordinator.transaction.TransactionCoordinator)
> {code}
> After rollback, the second message is sent to a different partition than the first message.

> Upon, transaction commit, {{org.apache.kafka.clients.producer.internals.TransactionManager}}
may enqueue the request {{addPartitionsToTransactionHandler}}:
> {code}
> private TransactionalRequestResult beginCompletingTransaction(TransactionResult transactionResult)
>         if (!newPartitionsInTransaction.isEmpty())
>             enqueueRequest(addPartitionsToTransactionHandler());
>         EndTxnRequest.Builder builder = new EndTxnRequest.Builder(transactionalId, producerIdAndEpoch.producerId,
>                 producerIdAndEpoch.epoch, transactionResult);
>         EndTxnHandler handler = new EndTxnHandler(builder);
>         enqueueRequest(handler);
>         return handler.result;
>     }
> {code}
> As can be seen, the condition is fulfilled if {{newPartitionsInTransaction}} is non-empty.
I suspect because the second message goes to a different partition, this condition is satisfied.
> In {{KafkaApis.scala}}, I can see that {{handleAddPartitionToTxnRequest}} may eventually
call {{TransactionMetadata#prepareAddPartitions}}:
> {code}
>  def prepareAddPartitions(addedTopicPartitions: immutable.Set[TopicPartition], updateTimestamp:
Long): TxnTransitMetadata = {
>     val newTxnStartTimestamp = state match {
>       case Empty | CompleteAbort | CompleteCommit => updateTimestamp
>       case _ => txnStartTimestamp
>     }
>     prepareTransitionTo(Ongoing, producerId, producerEpoch, txnTimeoutMs, (topicPartitions
++ addedTopicPartitions).toSet,
>       newTxnStartTimestamp, updateTimestamp)
>   }
> {code}
> Note that the method's first argument {{newState}} of is always *Ongoing* here. I suspect
that this puts the transaction, which should be aborted, to _Ongoing_ again.

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