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Subject: Fundamentals Question on CoucheDB's append only b+tree.
Date: Tue, 13 Mar 2012 17:26:31 -0000
Message-ID: <5293620AC1A91649BDD85E5380BC837A79A808@uksrpblkexb02.detica.com>
Thread-Topic: Fundamentals Question on CoucheDB's append only b+tree.
Thread-Index: Ac0BPm38UVfADao8QfSvz3JvdWcXqA==
From: "Davies, Owain" <Owain.Davies@baesystemsdetica.com>
To: <dev@couchdb.apache.org>

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Hi,

I have been reading the couchDB guide, particularly the appendix on the
power of b-trees. As I understand it couchdb uses a b+tree, in which the
leaf nodes have pointers to their siblings to facilitate quick in-order
and reverse in-order enumeration of the documents in the b+tree.

When a document is modified (or added), then the document is appended to
the file, the leaf node is cloned and updated to point to the new
document. However in order to maintain the linked list between the
sibling leaf nodes, you would need to update the adjacent link nodes
(creating new leaf nodes appended onto the end of the file), this will
eventually require that the whole tree is replicated, not just the node
on the path to the effected leaf node.

I do not think this can be the case, could somebody point out where I
have made the mistake?=20

Thanks,

Owain

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