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Posted to mapreduce-issues@hadoop.apache.org by "Karthik Kambatla (JIRA)" <ji...@apache.org> on 2013/03/28 03:53:16 UTC

[jira] [Commented] (MAPREDUCE-5110) Long task launch delays can lead to multiple parallel attempts of the task

    [ https://issues.apache.org/jira/browse/MAPREDUCE-5110?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13616000#comment-13616000 ] 

Karthik Kambatla commented on MAPREDUCE-5110:
---------------------------------------------

The issue can be reproduced by applying the above patch on a 4 node cluster (8 map/reduce slots) with mapred.tasktracker.expiry.interval set to 1000 and running terasort on 20 GB data.
                
> Long task launch delays can lead to multiple parallel attempts of the task
> --------------------------------------------------------------------------
>
>                 Key: MAPREDUCE-5110
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-5110
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: tasktracker
>    Affects Versions: 1.1.2
>            Reporter: Karthik Kambatla
>            Assignee: Karthik Kambatla
>         Attachments: expose-mr-5110.patch
>
>
> If a task takes too long to launch, the JT expires the task and schedules another attempt. The earlier attempt can start after the later attempt leading to two parallel attempts running at the same time. This is particularly an issue if the user turns off speculation and expects a single attempt of a task to run at any point in time.

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