[jira] [Commented] (KAFKA-955) After a leader change, messages sent with ack=0 are lost

["Jun Rao (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-955?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13727824#comment-13727824 ] 

Jun Rao commented on KAFKA-955:
-------------------------------

Thanks for patch v2. Some more comments.

20. testSendWithAckZeroDeadBroker(): I am not sure if the unit test does what you want. First of all, setup() will always start brokers for each test unless you explicitly shut them down. So, in this test, the brokers are not dead. Second, the test doesn't really test that the socket is closed after error. I suggest that we add a new test in SyncProducerTest. We send a request with ack=0 with a large message. After that, we can try to send a new request again and we should hit a socket I/O exception. We may have to wait for some time between the two requests.
                
> After a leader change, messages sent with ack=0 are lost
> --------------------------------------------------------
>
>                 Key: KAFKA-955
>                 URL: https://issues.apache.org/jira/browse/KAFKA-955
>             Project: Kafka
>          Issue Type: Bug
>            Reporter: Jason Rosenberg
>            Assignee: Guozhang Wang
>         Attachments: KAFKA-955.v1.patch, KAFKA-955.v1.patch, KAFKA-955.v2.patch
>
>
> If the leader changes for a partition, and a producer is sending messages with ack=0, then messages will be lost, since the producer has no active way of knowing that the leader has changed, until it's next metadata refresh update.
> The broker receiving the message, which is no longer the leader, logs a message like this:
> Produce request with correlation id 7136261 from client  on partition [mytopic,0] failed due to Leader not local for partition [mytopic,0] on broker 508818741
> This is exacerbated by the controlled shutdown mechanism, which forces an immediate leader change.
> A possible solution to this would be for a broker which receives a message, for a topic that it is no longer the leader for (and if the ack level is 0), then the broker could just silently forward the message over to the current leader.

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