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From Mark Robson <mar...@gmail.com>
Subject Re: How to store tree structure in Cassandra
Date Wed, 28 Oct 2009 07:35:17 GMT
2009/10/28 Brink <jqworld@163.com>

> Hi All,
>
> For a DMS, I want to replace MySQL with Cassandra to store file/folder
> nodes. Current I use adjacency list model to stores nodes hierarchy. The
> shortage of the adjacency list model is the expensive traversal cost. While
> I want to navigate the entire workspace or folder in hierarchy, I have to
> execute multiple queries (for each sub folder). In addition, special care
> must be taken when deleting nodes because of the potential for orphaning an
> entire sub-tree in the process (delete a folder and all of its children may
> be orphaned). How to design to store files/folders'node as tree structure in
> Cassandra?
>

Can you not use the entire path as a key? That would enable a recursive
directory scan to become a simple range scan (which is supported provided
you use the OrderedPartitioner)

The downside is that if you want to scan the immediate children you get a
lot of additional junk you have to discard.

Storing redundant information in Cassandra (or any such database) is not an
unusual solution - if you want very high scalability as well as good
performance in competing cases (e.g. store the same thing under several
keys)

Mark

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