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From "Arun C Murthy (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1984) some reducer stuck at copy phase and progress extremely slowly
Date Mon, 12 Nov 2007 10:26:51 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1984?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12541731
] 

Arun C Murthy commented on HADOOP-1984:
---------------------------------------

Ok, after some more thought...

Initial back-off of 2s is too aggressive - it means that it only takes 5 failures in 1minute
(2 + 4 + 8 + 16 + 32 = 62s) to send a fetch-failure notification to the JT (see HADOOP-1158)
and thus doesn't sufficiently account for transient problems faced by the tasktracker's jetty
(tt on which the map ran).

I propose we peg the starting back-off at 8s which means that it takes approximately 4mins
for one notification to be sent to the JT i.e. (8 + 16 + 32 + 64 + 128 = 249s).

Also, we need to maintain a per-host fetch-failure count since the penaltyBox is also maintained
on a per-host basis.

> 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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