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Date: Tue, 5 Oct 2010 13:56:38 -0400 (EDT)
From: "Sanjay Radia (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Subject: [jira] Commented: (HDFS-1073) Simpler model for Namenode's fs Image
 and edit Logs
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    [ https://issues.apache.org/jira/browse/HDFS-1073?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12918088#action_12918088 ] 

Sanjay Radia commented on HDFS-1073:
------------------------------------

  >> In order to do an offline fsck one can needs to dump the block map; ...
>Sorry, can you elaborate a little bit here?  ...

This has nothing to do with Backup namenode. Currently the fsck is implemented inside the
NN. We would like do this offiline. So one could do a dump of the block map and at the start of the dump record the transaction id. I believe that with this one would not have lock the FSNamspace.

The above is just one use case of the transaction id. There are others. For example, during
failover the transaction id would be useful for determining on one has the latest edits. 

> Simpler model for Namenode's fs Image and edit Logs 
> ----------------------------------------------------
>
>                 Key: HDFS-1073
>                 URL: https://issues.apache.org/jira/browse/HDFS-1073
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Sanjay Radia
>            Assignee: Todd Lipcon
>         Attachments: hdfs1073.pdf
>
>
> The naming and handling of  NN's fsImage and edit logs can be significantly improved resulting simpler and more robust code.

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