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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1521) Persist transaction ID on disk between NN restarts
Date Wed, 16 Mar 2011 18:59:29 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1521?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13007628#comment-13007628
] 

Konstantin Shvachko commented on HDFS-1521:
-------------------------------------------

Ivan, you are reaching back one way or another.
{{namesystem.getImage().getStorage()}} points exactly where the version is.
I don't see any benefits in introducing another nnStorage variable. Do you?
It just obscures which layout version you are trying to get, and confuses
people there could be some other NNStorage that is different from the image one.
I would do this only if you could eliminate the reference to namesystem.
But it doesn't look it is possible.

> 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-1521.3.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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