[jira] Commented: (HADOOP-1077) Race condition in fetching map outputs (might lead to hung reduces)

["Devaraj Das (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-1077?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12478722 ] 

Devaraj Das commented on HADOOP-1077:
-------------------------------------

A clarification (the description should read as follows):
Sometimes when a map task is lost while the map-output fetch is happening from the TT for that task, and the lost map has, *in the meantime*, successfully executed on some other node, the event for that successful execution is lost at the fetching TT. The fetching TT might eventually fail to fetch the output for the lost task, but then since the event for the new run of the lost map might also have been lost, the fetching TT might hang.


> Race condition in fetching map outputs (might lead to hung reduces)
> -------------------------------------------------------------------
>
>                 Key: HADOOP-1077
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1077
>             Project: Hadoop
>          Issue Type: Bug
>          Components: mapred
>            Reporter: Devaraj Das
>         Assigned To: Devaraj Das
>
> Sometimes when a map task is lost while the map-output fetch is happening from the TT for that task, and the lost map has successfully executed on some other node, the event for that successful execution is lost at the fetching TT. The fetching TT might eventually fail to fetch the output for the lost task, but then since the event for the new run of the lost map might also have been lost, the fetching TT might hang.
> This "hung" problem was discovered while working on HADOOP-1060.

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