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https://issues.apache.org/jira/browse/HDFS-7007?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14124953#comment-14124953
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Steve Loughran commented on HDFS-7007:
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The current NN code isn't suitable for subclassing, and the fact that
BackupNode does exactly that is a bit dangerous.
Specifically, the NN ctor calls {{initialize()}} which appears designed to be
overrridden ... but subclasses won't be fully constructed until this happens.
The DNs are worse -they start threads in their ctors, which are one of the big
forbidden actions of Java.
I'd propose making the NN and DN YARN services first, so we have a nice
consistent override model. As with the RM, we can make them subclasses of
CompositeService, so making it easy to add children.
This does not have to be done in the consensus node branch ... it can be done
in trunk.
> Interfaces to plugin ConsensusNode.
> -----------------------------------
>
> Key: HDFS-7007
> URL: https://issues.apache.org/jira/browse/HDFS-7007
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: namenode
> Affects Versions: 3.0.0
> Reporter: Konstantin Shvachko
>
> This is to introduce interfaces in NameNode and namesystem, which are needed
> to plugin ConsensusNode.
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