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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2223) Untangle depencencies between NN components
Date Wed, 10 Aug 2011 23:45:27 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2223?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13082771#comment-13082771
] 

Todd Lipcon commented on HDFS-2223:
-----------------------------------

bq. Should FSImage.namesystem be removed?
Yes - it is removed in this patch. I wasn't able to easily remove it from BackupImage at this
point, without changing a bunch of the BN around. So, I left it in the subclass only.

bq. Why not container for FSDirectory, FSImage, FSEditlog, as they are very closely related
to namespace.
bq. Should NNStorage belong to NameNode?

I think FSEditLog still belongs below FSImage, as it's part of the "image on disk" in a sense,
and their lifecycle is tightly related.
Moving NNStorage up into NameNode does make a certain amount of sense to me, but I didn't
want to bite off too much in one patch.


Do you think the changes in the attached patch are good, even if they're not a complete cleanup
of everything? If so, let's commit this and then do some more work in another JIRA, just so
each small improvement is easy to review?

> Untangle depencencies between NN components
> -------------------------------------------
>
>                 Key: HDFS-2223
>                 URL: https://issues.apache.org/jira/browse/HDFS-2223
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: name-node
>    Affects Versions: 0.23.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: hdfs-2223-1.txt, hdfs-2223-2.txt, hdfs-2223-3.txt, hdfs-2223-4.txt
>
>
> Working in the NN a lot for HA (HDFS-1623) I've come across a number of situations where
the tangled dependencies between NN components has been problematic for adding new features
and for testability. It would be good to untangle some of these and clarify what the distinction
is between the different components: NameNode, FSNamesystem, FSDirectory, FSImage, NNStorage,
and FSEditLog

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