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https://issues.apache.org/jira/browse/TEZ-3972?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16596684#comment-16596684
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Jonathan Eagles commented on TEZ-3972:
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[~kshukla], I think we may need to protect ourselves from division by zero to
avoid this in race conditions. What do you think?
> Tez DAG can hang when a single task fails to fetch
> --------------------------------------------------
>
> Key: TEZ-3972
> URL: https://issues.apache.org/jira/browse/TEZ-3972
> Project: Apache Tez
> Issue Type: Bug
> Affects Versions: 0.9.1
> Reporter: Kuhu Shukla
> Assignee: Kuhu Shukla
> Priority: Major
> Attachments: TEZ-3972.001.patch, TEZ-3972.002.patch
>
>
> Description of the hung DAG:
> A DAG with 2 vertices. {{Map}} Vertex has 22k maps, downstream vertex
> {{Reduce}} has 1009 tasks. All tasks succeed but one, which hangs. This one
> task (attempt) is doing a local fetch from a node that (now) has a bad disk.
> It fails to fetch and reports to the AM for the offending input attempt
> identifiers. However the AM does not schedule a re-run as
> {{uniquefailedOutputReports}} size is 1 (since only this task attempt failed
> to fetch) and failure fraction is not met. The denominator for this fraction
> is the total number of tasks. That causes the re-run to never occur. This
> JIRA tracks the AM side of the change to alleviate this problem.
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