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From "Ivan Kelly (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1521) Persist transaction ID on disk between NN restarts
Date Wed, 16 Mar 2011 20:00:29 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1521?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13007667#comment-13007667
] 

Ivan Kelly commented on HDFS-1521:
----------------------------------

I've submitted a version without the storage change. 

The difference in "reaching back" with my former version was that FSImageFormat did not have
to know about the existence of the method getImage() on FSNameSystem, and of the method getStorage()
on FSImage. So it breaks a static code dependency. Im don't feel very strongly about it either
way though, so I've submitted a patch without it.

I've looked at breaking the dependency on FSNameSystem before, and it does look to be possible,
but would be a lot of work. Really FSImageFormat should only need the FSDirectory reference.

> Persist transaction ID on disk between NN restarts
> --------------------------------------------------
>
>                 Key: HDFS-1521
>                 URL: https://issues.apache.org/jira/browse/HDFS-1521
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: name-node
>    Affects Versions: 0.22.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: FSImageFormat.patch, HDFS-1521.diff, HDFS-1521.diff, HDFS-1521.diff,
HDFS-1521.diff, HDFS-1521.diff, hdfs-1521.3.txt, hdfs-1521.4.txt, hdfs-1521.5.txt, hdfs-1521.txt,
hdfs-1521.txt, hdfs-1521.txt
>
>
> For HDFS-1073 and other future work, we'd like to have the concept of a transaction ID
that is persisted on disk with the image/edits. We already have this concept in the NameNode
but it resets to 0 on restart. We can also use this txid to replace the _checkpointTime_ field,
I believe.

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