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From "Arun C Murthy (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-1862) reduces are getting stuck trying to find map outputs
Date Tue, 11 Sep 2007 10:35:34 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-1862?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Arun C Murthy updated HADOOP-1862:
----------------------------------

    Attachment: HADOOP-1862_debug.patch

Ok, I was fortunate to be able to look at an actual job exhibiting this same behaviour (thanks
to Christian and HADOOP-1874) and here are some insights:

Essentially there seems like a issue with {{TaskCompletionEvent}}s received by the {{ReduceTask}}.
More than one *stuck* reducer (looking for map outputs) never actually scheduled a copy from
the maps from which it is missing outputs, which leads me to believe that there is an issue
with missing {{TaskCompletionEvents}}s.

The other minor bug is the one I pointed out in my previous comment, so I've attached another
patch which incorporates:
a) previous fix
b) a debug statement to help track the received {{TaskCompletionEvent}}s at the {{Reduce}}
task.

Christian: I'd appreciate if you could try this out... Thanks!

> reduces are getting stuck trying to find map outputs
> ----------------------------------------------------
>
>                 Key: HADOOP-1862
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1862
>             Project: Hadoop
>          Issue Type: Bug
>          Components: mapred
>    Affects Versions: 0.14.1
>            Reporter: Owen O'Malley
>            Assignee: Owen O'Malley
>            Priority: Blocker
>             Fix For: 0.15.0
>
>         Attachments: HADOOP-1862_debug.patch, HADOOP-1862_prelim.patch
>
>
> Some of the reduces have been stuck for hours looking for 137 map outputs. When I look
at the job events all 2600 of the maps have succeeded. There have been lots of lost task trackers
and shuffle failures. The maps have been run between 1 to 6 times each. I do see some of the
events in the task event log are marked OBSOLETE.

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