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From "Arun C Murthy (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-2639) Reducers stuck in shuffle
Date Mon, 28 Jan 2008 18:53:34 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-2639?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12563245#action_12563245
] 

Arun C Murthy commented on HADOOP-2639:
---------------------------------------

Ok, looks like there is some disconnect...

While implementing HADOOP-2247, I remember that the following code: 

{noformat}
    float failureRate = (float)fetchFailures / runningReduceTasks;
{noformat}

is to mean: _Check if there are too many currently running reduce TIPs are complaining about
this map._

I had a discussion with Amar and he clarified that he was considering the counter as _currently
running reduce task-attempts_ and not _currently running reduce TIPs_ as was the original
intention... and hence this debate/disconnect.

Given that, I think the right fix is for us to figure _why_ the *runningReduceTasks* counter
is wrongly turning -ve and fix the wrong decrement... 

Thoughts?

> Reducers stuck in shuffle
> -------------------------
>
>                 Key: HADOOP-2639
>                 URL: https://issues.apache.org/jira/browse/HADOOP-2639
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: mapred
>            Reporter: Amareshwari Sri Ramadasu
>            Assignee: Amar Kamat
>            Priority: Blocker
>             Fix For: 0.16.0
>
>         Attachments: HADOOP-2639.patch
>
>
> I started sort benchmark on 500 nodes. It has 40000 maps and 900 reducers.
> There are 11 reducers stuck in shuffle with 33% progress. I could see a node down which
ran 80 maps on it. And all these reducers are trying to fetch map output from that node. 

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