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Date: Wed, 26 Mar 2008 09:49:26 -0700 (PDT)
From: "Amar Kamat (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=12582341#action_12582341 ] 

Amar Kamat commented on HADOOP-2175:
------------------------------------

In the default case it will take atleast 5min to send a notification. The reducer code is such that only one map task per host is tried at a time. It will try a new map task only if the earlier one succeeds/fails.

> 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: Amar Kamat
>             Fix For: 0.17.0
>
>         Attachments: HADOOP-2175-v1.1.patch, HADOOP-2175-v1.patch, HADOOP-2175-v2.patch, HADOOP-2175-v2.patch
>
>
> 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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