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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-227) Namespace check pointing is not performed until the namenode restarts.
Date Mon, 27 Nov 2006 21:58:22 GMT
    [ http://issues.apache.org/jira/browse/HADOOP-227?page=comments#action_12453716 ] 
            
Doug Cutting commented on HADOOP-227:
-------------------------------------

A checkpointing approach you don't seem to evaluate is making it very cheap to clone the in-memory
 tree, specifically, by always copying nodes between the root and each edit.  That way one
can checkpoint by just grabbing the pointer to the root, and then writing the shadow tree
in the background.  No merging required, no complex re-sorting of operations, etc.

> 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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