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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1521) Persist transaction ID on disk between NN restarts
Date Fri, 10 Dec 2010 06:20:01 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1521?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12970088#action_12970088
] 

dhruba borthakur commented on HDFS-1521:
----------------------------------------

I am fine creating another persistent id here.

> @Dhruba > can we instead use the generationStamp that the NN maintains persistently
on disk?
> Isn;t the txId different - it is increment per transaction. The G# isn't.

@Sanjay: I was mentioning that we already have a sequentially increasing persistent id that
we store on disk. This is the generation stamp. it is currently incremented only during file
creations and error occurances. We could decide to increment it for every transaction too
for this JIRA.

> 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
>    Affects Versions: 0.22.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>             Fix For: 0.22.0
>
>         Attachments: 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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