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Date: Tue, 1 Apr 2008 07:36:25 -0700 (PDT)
From: "Runping Qi (JIRA)" <jira@apache.org>
To: core-dev@hadoop.apache.org
Subject: [jira] Commented: (HADOOP-3130) Shuffling takes too long to get the
 last map output.
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    [ https://issues.apache.org/jira/browse/HADOOP-3130?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12584154#action_12584154 ] 

Runping Qi commented on HADOOP-3130:
------------------------------------


>From timing point view, 

the following two are equivalent:
{code}
connect( , N_units_timeout);
{code}

{code}
lastException=null;
lastTime=-1;
for (int i = 0; i < N; i++) {
try {
    connect( , N_units_timeout);
    break;
}
catch (IOException e) {
    lastException = e;
    lastTime = i;
}
}
if (lastTime==N-1) throw lastException;

{code}

But the second one has a much stronger liveness.


> Shuffling takes too long to get the last map output.
> ----------------------------------------------------
>
>                 Key: HADOOP-3130
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3130
>             Project: Hadoop Core
>          Issue Type: Bug
>            Reporter: Runping Qi
>         Attachments: HADOOP-3130.patch, shuffling.log
>
>
> I noticed that towards the end of shufflling, the map output fetcher of the reducer backs off too aggressively.
> I attach a fraction of one reduce log of my job.
> Noticed that the last map output was not fetched in 2 minutes.

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