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From "Milind Bhandarkar (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-227) Namespace check pointing is not performed until the namenode restarts.
Date Tue, 28 Nov 2006 01:32:22 GMT
    [ http://issues.apache.org/jira/browse/HADOOP-227?page=comments#action_12453772 ] 
            
Milind Bhandarkar commented on HADOOP-227:
------------------------------------------

Well, the sort-merge approach does not seem performant anyway if the number of renames is
large. So, I am adding the copy-on-write (Dhruba's comment on HADOOP-334) to the proposal.
This proposal suggests adding a clone member to every node. While checkpointing is in progress,
change to a node is instead made to a clone. When periodic checkpointing is finished, the
checkpointer resets the clones by making them actual nodes. I will write up a better description
and post as RFC soon.


> Namespace check pointing is not performed until the namenode restarts.
> ----------------------------------------------------------------------
>
>                 Key: HADOOP-227
>                 URL: http://issues.apache.org/jira/browse/HADOOP-227
>             Project: Hadoop
>          Issue Type: Bug
>          Components: dfs
>    Affects Versions: 0.2.0
>            Reporter: Konstantin Shvachko
>         Assigned To: Konstantin Shvachko
>
> In current implementation when the name node starts, it reads its image file, then
> the edits file, and then saves the updated image back into the image file.
> The image file is never updated after that.
> In order to provide the system reliability reliability the namespace information should
> be check pointed periodically, and the edits file should be kept relatively small.

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