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