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