[jira] [Commented] (TEZ-3974) Tez: Correctness regression of TEZ-955 in TEZ-2937

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/TEZ-3974?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16568977#comment-16568977 ] 

ASF GitHub Bot commented on TEZ-3974:
-------------------------------------

GitHub user beltran opened a pull request:

    https://github.com/apache/tez/pull/29

    TEZ-3974: Correctness regression of TEZ-955 in TEZ-2937

    

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

    $ git pull https://github.com/beltran/tez TEZ-3974

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

    https://github.com/apache/tez/pull/29.patch

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

    This closes #29
    
----
commit 7d0d621482e9ab8357b5b5c13a89ff8f1b9438e5
Author: Jaume Marhuenda <ja...@...>
Date:   2018-08-03T22:40:09Z

    TEZ-3974: Correctness regression of TEZ-955 in TEZ-2937

----


> Tez: Correctness regression of TEZ-955 in TEZ-2937
> --------------------------------------------------
>
>                 Key: TEZ-3974
>                 URL: https://issues.apache.org/jira/browse/TEZ-3974
>             Project: Apache Tez
>          Issue Type: Bug
>            Reporter: Gopal V
>            Priority: Critical
>
> TEZ-2937 might have introduced a race condition for Tez output events, along with TEZ-2237
> {code}
>       // Close the Outputs.
>       for (OutputSpec outputSpec : outputSpecs) {
>         String destVertexName = outputSpec.getDestinationVertexName();
>         initializedOutputs.remove(destVertexName);
>         List<Event> closeOutputEvents = ((LogicalOutputFrameworkInterface)outputsMap.get(destVertexName)).close();
>         sendTaskGeneratedEvents(closeOutputEvents,
>             EventProducerConsumerType.OUTPUT, taskSpec.getVertexName(),
>             destVertexName, taskSpec.getTaskAttemptID());
>       }
>       // Close the Processor.
>       processorClosed = true;
>       processor.close();
> {code}
> As part of TEZ-2237, the outputs send empty events when the output is closed without being started (which happens in task init failures).
> These events are obsoleted when a task fails and this happens in the AM, but not before the dispatcher looks at them.
> Depending on the timing, the empty events can escape obsoletion & be sent to a downstream task.
> This gets marked as a SKIPPED event in the downstream task, which means that further obsoletion events sent to the downstream task is ignored (because a zero byte fetch is not repeated on node failure).
> So the downstream task can exit without actually waiting for the retry of the failed task and cause silent dataloss in case where the retry succeeds in another attempt.
> So if processor.close() throws an exception, this introduce a race condition and if the AM is too fast, we end up with correctness issues.
> This was originally reported in TEZ-955



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