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Posted to dev@tez.apache.org by "Kuhu Shukla (JIRA)" <ji...@apache.org> on 2018/07/19 21:19:00 UTC

[jira] [Created] (TEZ-3972) Tez DAG can hang when a single task fails to fetch

Kuhu Shukla created TEZ-3972:
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             Summary: 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


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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