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From "Ivan Kelly (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3958) Integrate upgrade/finalize/rollback with external journals
Date Wed, 19 Sep 2012 09:37:07 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3958?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13458528#comment-13458528
] 

Ivan Kelly commented on HDFS-3958:
----------------------------------

I guess an "upgrade" operation itself isn't really needed, as when you upgrade the NN, it
merges the editlog with the image. Then the upgraded NN can use what looks like a newly formatted
editlog. Doing this on a live system with multiple possible writers to the editlog could be
problematic though. 

Snapshotting itself shouldn't be too difficult for us, as we just need to take a snapshot
of the zk tree at a certain znode version.
                
> Integrate upgrade/finalize/rollback with external journals
> ----------------------------------------------------------
>
>                 Key: HDFS-3958
>                 URL: https://issues.apache.org/jira/browse/HDFS-3958
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: name-node
>    Affects Versions: 3.0.0
>            Reporter: Todd Lipcon
>
> Currently the NameNode upgrade/rollback/finalize framework only supports local storage.
With edits being stored in pluggable Journals, this could create certain difficulties - in
particular, rollback wouldn't actually rollback the external storage to the old state.
> We should look at how to expose the right hooks to the external journal storage to snapshot/rollback/finalize.

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