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From "Chris Nauroth (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-11034) Provide a command line tool to clear decommissioned DataNode information from the NameNode without restarting.
Date Wed, 26 Oct 2016 23:45:58 GMT

    [ https://issues.apache.org/jira/browse/HDFS-11034?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15610068#comment-15610068
] 

Chris Nauroth commented on HDFS-11034:
--------------------------------------

Hello [~GergelyNovak].

If the decommissioned host is removed from the {{dfs.hosts.exclude}} file, followed by running
{{hdfs dfsadmin -refreshNodes}}, then the host is no longer considered to be excluded.  If
the DataNode process is still running, or if it's restarted accidentally, then that DataNode
will re-register with the NameNode, come back into service and become a candidate for writing
new blocks.

I was imagining a new workflow, where the host remains decommissioned, but the administrator
has a way to clear out the in-memory tracked state about that node.  It's interesting that
you brought up the exclude file.  Since that's already the existing mechanism for inclusion/exclusion
of hosts, I wonder if there is a way to enhance it to cover this use case, so that administrators
wouldn't need to learn a new command.  I'll think about it more (and comments are welcome
from others who have ideas too).

> Provide a command line tool to clear decommissioned DataNode information from the NameNode
without restarting.
> --------------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-11034
>                 URL: https://issues.apache.org/jira/browse/HDFS-11034
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode
>            Reporter: Chris Nauroth
>            Assignee: Gergely Novák
>
> Information about decommissioned DataNodes remains tracked in the NameNode for the entire
NameNode process lifetime.  Currently, the only way to clear this information is to restart
the NameNode.  This issue proposes to add a way to clear this information online, without
requiring a process restart.



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