[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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