Re: The State of Native XML databases

[Ilya Sterin]

On 8/21/07, Jeff Dexter <http://x-query.com/mailman/listinfo/talk> wrote:
> OK, I don't want to sounds like I'm always disagreeing, but I disagree :)
>
> I'd be curious to hear from users on this, but in my experience the notion
> of a "page" is too nebulous for most users. Granted, it's sub-document, but
> what subset of the document does it represent. If there's a clear mapping
> between a page and the nodes in the document, great, but I'd still argue
> that node level granularity is about the most granular you can get, and
> users understand what a node is (well, except for text node which still
> seems to cause the odd confused look).

Jeff, absolutely.  Page level locking is not something that a user can
control, I believe, right, so there is an undefined level of
concurrency that it might buy, but we never know.  Updating multiple
nodes on the same page would be no different than updating same nodes
with document level locking.  Now, yes, it probably does reduce the
possibility for lock contention, but that's not enough.  Node level
locking is granular and controllable from the standpoint of what  a
logic record is.  A user can employ multiple data access patterns they
wish to ensure the maximum level of concurrency and also with your
extensions for lock control, they can easily promote the locking to
any level they like.

>
> On a side note, while node level locks may be the most granular, some update
> operations may require locking multiple nodes. For instance, if you replace
> an element that has attributes and children, a lock of the element may imply
> a lock of its attributes and descendants as well.

Yes, that is how it should be done.  I'm also thinking of
insert/delete operations, that basically change parent's child counts.
 Those operations should probably perform a more extensive lock and
you can promote those higher up.

Ilya

>
> Jeff.
>
> -----Original Message-----
> From: http://x-query.com/mailman/listinfo/talk [mailto:http://x-query.com/mailman/listinfo/talk] On Behalf
> Of John Snelson
> Sent: Tuesday, August 21, 2007 7:23 AM
> To: Ronald Bourret
> Cc: http://x-query.com/mailman/listinfo/talk
> Subject: Re:  Re: The State of Native XML databases
>
> Ronald Bourret wrote:
> > Does anybody know how many native XML databases actually support
> > node-level locking? My impression is that most support document-level
> > locking.
>
> As I mentioned before, Berkeley DB XML has sub-document level locking in the
> form of page level locking with user-configurable page size.
>
> Talking about "node-level locking" is a bit of a red-herring - what you
> should be interested in is sub-document granularity locking, which in itself
> is only a means to achieve high concurrency in writes.
>
> John
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