[Mulgara-dev] Model metadata
Andrae Muys
andrae at netymon.com
Wed Mar 7 05:36:29 UTC 2007
On 07/03/2007, at 12:06 PM, Robert Turner wrote:
> Hi All,
>
> Here's an idea for your consideration.
>
> I am thinking it may be useful to add some extra model metadata to
> the System (#) model? It currently contains statement's about model
> type, but it may be useful to also include statements like a
> created timestamp, last modified, version number etc.
Yes we could put all this in the system model, but why? It's a
simple process to write a trivial resolver that will track all this
for you, and this would also simplify deciding _what_ additional
metadata should be provided. Ultimately the best place to store
metadata concerning a set of models is another model - if the client
wants this done transparently, then this is a job for a new resolver,
not a change to mulgara's core.
> Another "out-there" use of a version number could potentially be
> within transactions, especially if the statement store becomes
> journal-based. The model could be rolled back to a previous version
> or queried/read from as it was in a previous version (revision)...
> think CVS/SVN. I know this is not a new idea, but a (globally query
> able) version number may come in handy if it were to be implemented.
Well there are not plans or even thoughts of moving to a journal-
based system - in fact the current design of XA2 is moving us further
in the opposite direction. Multi-version is possible, but it comes
at a significant performance cost of either the normal case of
operations against head; or substantially increased vacuum overhead.
I don't believe it is feasible to provide full multi-version support
at this scale, but of course I'm happy to be proven wrong.
Andrae
--
Andrae Muys
andrae at netymon.com
Principal Mulgara Consultant
Netymon Pty Ltd
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