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From Jeff Yemin <jeff.ye...@gmail.com>
Subject Re: [jr3] Flat hierarchy
Date Thu, 18 Feb 2010 15:28:19 GMT

I think Jukka is correct that the correct use of B-trees is to use one for
each list of child nodes, not as a way to model the entire hierarchy.  I've
seen this implementation approach used for similar use cases, so I know that
it can work.  And there are modifications that can easily be applied to
B-trees that deal with arbitrary (not based on a key) ordering of the nodes,
even allowing you to skip to the n-th child efficiently (without having to
traverse the entire tree).

The part that's not clear to me is how this can be efficiently combined with
an append-only storage format that's being discussed on the "[jr3] Unified
persistence" thread.  It wouldn't be good if every time a list of children
is modified the persistence layer has to make a complete copy of the
modified B-tree, as that would defeat the purpose of use a b-tree in the
first place, wouldn't it?

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