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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-334) Redesign the dfs namespace datastructures to be copy on write
Date Mon, 06 Nov 2006 19:53:39 GMT
    [ http://issues.apache.org/jira/browse/HADOOP-334?page=comments#action_12447516 ] 
            
Doug Cutting commented on HADOOP-334:
-------------------------------------

The simplest copy-on-write approach would:

1. Keep a pointer to the root of the tree.
2. For any change, copy all structures on the path between the root and the change, and reset
the root.
3. To checkpoint, traverse the tree from the root.

Synchronization would be required around changes (single writer, multiple reader).

Allocating something proportional to the path length per change is probably fast enough. 
Do we have reason to think this would be too slow?

> 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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