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From "Sameer Paranjpye (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-334) Redesign the dfs namespace datastructures to be copy on write
Date Tue, 07 Nov 2006 04:22:38 GMT
    [ http://issues.apache.org/jira/browse/HADOOP-334?page=comments#action_12447623 ] 
            
Sameer Paranjpye commented on HADOOP-334:
-----------------------------------------

I'm not sure that overlapping diminishes debuggability. With a sequence number per node in
the image and edits we can completely validate an edits log. There are 3 kinds of node in
the image and edits:

a. Those that occur in the image but not in the edits. These must have a sequence number lower
than the lowest sequence number in the edits.
b. Those that occur in both, the "overlapping" ones. For each such node, the sequence number
in the image must match the sequence number of the last reference to the node in the edits
c. Those that occur in the edits but not in the image. These must occur in rename or delete
transactions only.

This validation is indirect, but I don't think it's incorrect.

> Redesign the dfs namespace datastructures to be copy on write
> -------------------------------------------------------------
>
>                 Key: HADOOP-334
>                 URL: http://issues.apache.org/jira/browse/HADOOP-334
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: dfs
>    Affects Versions: 0.4.0
>            Reporter: Owen O'Malley
>         Assigned To: Konstantin Shvachko
>
> The namespace datastructures should be copy on write so that the namespace does not need
to be completely locked down from user changes while the checkpoint is being made.

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