[Mulgara-dev] Model metadata

Paul Gearon gearon at ieee.org
Wed Mar 7 05:37:47 UTC 2007


I've always been surprised at the lack of statements found in the  
system model.  I just thought there'd be more to say about models  
beyond their type.  So this actually sounds good to me.

That said, I'm not so sure about the revision number on the model.   
It would have to be a delete/insert during a commit, which sounds  
messy.  More to the point, it sounds like it may have a performance  
impact.  Since Andrae has his head around transaction at the moment,  
he might be the person to ask.

BTW, if there IS a performance impact, it could be possible to have a  
resolver that does some of this work separate to the store, and get  
the update time from that.  That could be kept separate from the rest  
of the storage system, with minimal impact.

Paul

On Mar 6, 2007, at 8:06 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.
>
> Version number metadata could be very useful for statement caching  
> on remote consumers. For example, a client could cache statements  
> about multiple resources and check the revision number periodically  
> to determine if the model has changed since the last read. So  
> instead of frequently executing queries and serializing many  
> statements over the network, a single statement could be checked  
> periodically to see if the cache requires purging.
>
> Whenever a write operation is invoked, the version number for any  
> modified models would be incremented. The version number could also  
> be returned to the client via the Answer API whenever a query is  
> executed.
>
> 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.
>
> Let me know what you think. Any ideas, suggestions, comments or  
> hate mail?
>
> Thanks,
> Rob
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