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Date: Fri, 7 Mar 2008 06:19:46 -0800 (PST)
From: "Runping Qi (JIRA)" <jira@apache.org>
To: core-dev@hadoop.apache.org
Subject: [jira] Commented: (HADOOP-2175) Blacklisted hosts may not be able
 to serve map outputs
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    [ https://issues.apache.org/jira/browse/HADOOP-2175?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12576208#action_12576208 ] 

Runping Qi commented on HADOOP-2175:
------------------------------------


Re-executing the mappers will likely be the correct action in most cases.
Even for some cases where this is not optimal, its cost will not be that expensive.
Thus, I think that is the right behavior, before comebody comes up with a simple and effective alternative


> Blacklisted hosts may not be able to serve map outputs
> ------------------------------------------------------
>
>                 Key: HADOOP-2175
>                 URL: https://issues.apache.org/jira/browse/HADOOP-2175
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: mapred
>            Reporter: Runping Qi
>            Assignee: Arun C Murthy
>
> After a node fails 4 mappers (tasks), it is added to blacklist thus it will no longer accept tasks.
> But, it will continue serve the map outputs of any mappers that ran successfully there. 
> However, the node may not be able serve the map outputs either. 
> This will cause the reducers to mark the corresponding map outputs as from slow hosts, 
> but continue to try to get the map outputs from that node.
> This may lead to waiting forever.

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