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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7007) Interfaces to plugin ConsensusNode.
Date Sat, 06 Sep 2014 00:29:29 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7007?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14123884#comment-14123884
] 

Konstantin Shvachko commented on HDFS-7007:
-------------------------------------------

Another [observation|https://issues.apache.org/jira/browse/HDFS-6940?focusedCommentId=14109691&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14109691],
which [~atm] does, argues that subclassing of NameNode classes makes the implementation more
fragile (if I understood it correctly).
There is one essential advantage of subclassing. I can create a completely different sub-project,
recreate the package structure of the parent class and reuse methods classes of that package
in the parent class project, without modifying the parent project. That way the parent project
is completely independent of the new sub-project.
Example:
{code}
/hadoop-hdfs/
      org.apache.hadoop.hdfs.server.namenode.NameNode {}
/hadoop-cnode/
      org.apache.hadoop.hdfs.server.namenode.ConsensusNode implements NameNode {}
{code}
In this case you can modify and build hadoop-hdfs without taking into account hadoop-cnode.
And deal with CNode only on the integration stage. I thought such separation is desirable.

> 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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