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From "Kuhu Shukla (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (TEZ-3972) Tez DAG can hang when a single task fails to fetch
Date Fri, 24 Aug 2018 15:32:00 GMT

    [ https://issues.apache.org/jira/browse/TEZ-3972?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16591814#comment-16591814

Kuhu Shukla commented on TEZ-3972:

 [~jeagles], request for review/comments. Thanks a lot!

> 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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