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https://issues.apache.org/jira/browse/HDFS-14563?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16868006#comment-16868006
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Chao Sun commented on HDFS-14563:
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If every NN reads the file and does the loading, will this still run into the
DNS issue where each NN sees a different subset of DNs? after the DNS look
fails, the DN will be disallowed to communicate with the NN. I'm not sure how a
subsequent setNodeState will work in that scenario.
It is also pretty hard to check the differences between all the DNs (e.g.,
which DN is reporting to NN1 but not NN2, etc).
> Enhance interface about recommissioning/decommissioning
> -------------------------------------------------------
>
> Key: HDFS-14563
> URL: https://issues.apache.org/jira/browse/HDFS-14563
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: hdfs-client, namenode
> Reporter: He Xiaoqiao
> Assignee: He Xiaoqiao
> Priority: Major
> Attachments: HDFS-14563.001.patch, HDFS-14563.002.patch, mt_mode-2.txt
>
>
> In current implementation, if we need to decommissioning or recommissioning
> one datanode, the only way is add the datanode to include or exclude file
> under namenode configuration path then execute command `bin/hadoop dfsadmin
> -refreshNodes` and trigger namenode to reload include/exclude and start to
> recommissioning or decommissioning datanode.
> The shortcomings of this approach is that:
> a. namenode reload include/exclude configuration file from devices, if I/O
> load is high, handler may be blocked.
> b. namenode has to process every datnodes in include and exclude
> configurations, if there are many datanodes (very common for large cluster)
> pending to process, namenode will be hung for hundred seconds to wait
> recommision/decommision finish at the worst since holding write lock.
> I think we should expose one lightweight interface to support recommissioning
> or decommissioning single datanode, thus we can operate datanode using
> dfsadmin more smooth.
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