>> [off but interesting topic] > <cut> > >> What would be the corresponding database layout that would scale and I >> could get the total number of legs in the zoo or total number of >> animals in the zoo without join(s)? >> >> Cheers, >> Daniel >> >> [/off but interesting topic] >> > > That all comes down to the keywords, efficiency, robustness and > performance and you can only pick one of them. So which two can you > sacrifice? The good news is that it is only theoretical, if you have > your requirements (i.e. the query with the right results has to return > within an acceptable time for the user not to get frustrated) who cares > if it is not as fast as it theoretically could be? Especially if this > means you can sacrifice the theoretically performance for easier > deployment and maintenance. > > To get back to the layout question, if I need to have a count of the > legs at any given time, I would like to see the business process that > requires this operation.
Well, I gave the concrete example of zoo/cage/animal/leg because this *is* the business logic. I need to know for example the total number of animals, this is pretty understandable if you have a zoo. Or you mean that I should give another example? > Using the business process I could probably > narrow down the scope quite a bit like, it is not necessary to have a > precise count at time *now* but it is good enough to have an exact count > which is no more then 4 seconds old but the query does need to return > within 50 ms. No, I'd like to have the exact number at any given time. > One solution could be to build a central data warehouse where all info > is stored in. Then have satellite db's that does ETL syncing with the > central one. The layout of the satellites contain an optimised table > version for the queries you want to throw at it. Let's say I need to implement this on the google app engine, so I can't make too many choices on my own. On the GAE, how would I do this? Cheers, Daniel -- Psss, psss, put it down! - http://www.cafepress.com/putitdown -- http://mail.python.org/mailman/listinfo/python-list
