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From Jukka Zitting <jukka.zitt...@gmail.com>
Subject Re: [jr3] Flat hierarchy
Date Thu, 18 Feb 2010 13:14:40 GMT

On Thu, Feb 18, 2010 at 2:01 PM, Thomas Müller <thomas.mueller@day.com> wrote:
> The repository is one large b-tree, and each JCR node is a b-tree node
> (except for the JCR nodes that don't have any child nodes: those are
> b-tree leaves).

I don't think we can model the entire repository as a B-tree (it's
certainly a tree, but the B-tree restructuring and balancing features
don't apply). Instead I'd store the child node lists of each node as
separate B-trees.

> Path lookups would still be fast (the same speed as now), except for
> large child node lists that were re-ordered. The difference is only
> for large child node lists. There is a difference between 'orderable'
> nodes (have the ability to reorder the child node list) and actually
> 're-ordered' child node lists. Is it acceptable if new nodes appear in
> lexicographic order in the child node list?

Instead of modifying the standard insertion order semantics for
orderable nodes, we could add a "next" pointer to the B-tree entries
to overlay a linked list on top of the B-tree structure. This makes
the data structure more complex but allows us to maintain support for
orderable nodes.


Jukka Zitting

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