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From "Amar Kamat (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1984) some reducer stuck at copy phase and progress extremely slowly
Date Fri, 16 Nov 2007 12:33:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1984?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12543057
] 

Amar Kamat commented on HADOOP-1984:
------------------------------------

Consider the following strategy :
{code}
backoff (t) = backoff-init * backoff-base^{t-1}
   t = number of retries
   backoff-init = 4 sec
   backoff-base = 2
   max-t = 5
{code}
So now the backoff intervals are {{4, 8, 16, 32, 64, 128}},  {{sum = 252 = 4.2 min}} after
which the notification is sent to the jobtracker from the reduce. So 6 retries are made before
sending the notification.

> some reducer stuck at copy phase and progress extremely slowly
> --------------------------------------------------------------
>
>                 Key: HADOOP-1984
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1984
>             Project: Hadoop
>          Issue Type: Bug
>          Components: mapred
>    Affects Versions: 0.16.0
>            Reporter: Runping Qi
>            Assignee: Amar Kamat
>            Priority: Critical
>             Fix For: 0.16.0
>
>         Attachments: HADOOP-1984.patch
>
>
> In many cases, some reducers got stuck at copy phase, progressing extremely slowly.
> The entire cluster seems doing nothing. This causes a very bad long tails of otherwise
well tuned map/red jobs.

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