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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
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Amar Kamat commented on HADOOP-2175:
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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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