> The new BTree is made of  persistent instances, and these
> are cached in the client in the same way as other persistent objects.
> The Durus server knows nothing about BTrees.
>
> The nice thing about BTrees is that it takes less space to
> record each change.

Thank you David for the explanation. BTW I also noticed BTree lacks a
has_key method - is this an intentional move to shift usage towards
__contains__, in general?