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https://issues.apache.org/jira/browse/HADOOP-3232?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12595673#action_12595673
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Doug Cutting commented on HADOOP-3232:
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Oops.  I posted my previous comment before I saw your last comment.  You're 
right, I was confusing DU and DF.  And I missed the refresh in the ctor.  
Sorry!  That resolves most of my concerns.  Since this is called much more 
frequently than I was thinking, it makes sense for it not to be synchronous.  I 
think my only remaining concern is the default interval, which you've said 
you'd address.  Thanks!

> Datanodes time out
> ------------------
>
>                 Key: HADOOP-3232
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3232
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: dfs
>    Affects Versions: 0.16.2
>         Environment: 10 node cluster + 1 namenode
>            Reporter: Johan Oskarsson
>            Priority: Critical
>             Fix For: 0.18.0
>
>         Attachments: du-nonblocking-v1.patch, du-nonblocking-v2-trunk.patch, 
> hadoop-hadoop-datanode-new.log, hadoop-hadoop-datanode-new.out, 
> hadoop-hadoop-datanode.out, hadoop-hadoop-namenode-master2.out
>
>
> I recently upgraded to 0.16.2 from 0.15.2 on our 10 node cluster.
> Unfortunately we're seeing datanode timeout issues. In previous versions 
> we've often seen in the nn webui that one or two datanodes "last contact" 
> goes from the usual 0-3 sec to ~200-300 before it drops down to 0 again.
> This causes mild discomfort but the big problems appear when all nodes do 
> this at once, as happened a few times after the upgrade.
> It was suggested that this could be due to namenode garbage collection, but 
> looking at the gc log output it doesn't seem to be the case.

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