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https://issues.apache.org/jira/browse/MAPREDUCE-2764?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13095387#comment-13095387
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Nathan Roberts commented on MAPREDUCE-2764:
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After jitendra latest comment on HADOOP-7510, I think I know the answer to #2 
(please tell me if this if incorrect). When a new (205) client gets redirected 
to an old (204) datanode to stream the file contents, the service information 
within the token is ignored. The kind has to be right, but the service can be 
pretty much anything because the servlet is going to reconstruct the service 
field anyway.

> Fix renewal of dfs delegation tokens
> ------------------------------------
>
>                 Key: MAPREDUCE-2764
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2764
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>            Reporter: Daryn Sharp
>            Assignee: Daryn Sharp
>             Fix For: 0.20.205.0
>
>         Attachments: MAPREDUCE-2764-2.patch, MAPREDUCE-2764.patch, 
> delegation.patch
>
>
> The JT may have issues renewing hftp tokens which disrupt long distcp jobs.  
> The problem is the JT's delegation token renewal code is built on brittle 
> assumptions.  The token's service field contains only the "ip:port" pair.  
> The renewal process assumes that the scheme must be hdfs.  If that fails due 
> to a {{VersionMismatchException}}, it tries https based on another assumption 
> that it must be hftp if it's not hdfs.  A number of other exceptions, most 
> commonly {{IOExceptions}}, can be generated which fouls up the renewal since 
> it won't fallback to https.

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