On Wed, Apr 27, 2011 at 10:34 PM, Alex Mizrahi <killerst...@newmail.ru>wrote:
> > Currently, I do something along the lines of the following on the results > > on get-instance[s]-by-XXX functions: > > (remove-if #'(lambda (x) (not (member ',class-name (mapcar #'class-name > > (sb-mop:class-precedence-list x))))) lst :key #'class-of) > > if I want results on the whole inheritance chain, or > > (remove-if #'(lambda (x) (not (equal ',class-name x)))) lst :key > > #'class-of) if I want result on the specific class. > > I wonder why not just typep? > It should be enough to answer any reasonable class-related query. Yes I was wondering the same thing yesterday... Lisp newbie here. Not well acquainted with the tools yet :) > > Now I know that efficiency is the issue here, but my (naive , since I > > havent had performance problems yet) response to that is that since the > > the search is indexed anyway, does it really matter? > > I mean since the complexity of the search is logarithmic wont the > separate > > hierachical index implementation you propose have diminishing returns? > > If you consider only search then yes, in theory there should be no > significant difference. > > But if multiple instances are returned you'll just have more data read and > sent to the Lisp side, so it will be proportionally slower. > > Le'ts consider a situation when you have one base class and M subclasses, > and each subclass has N instances matching a query on average. > Then with simple inherited index you'll have N*M instances read from > database, while direct index on subclass would return only N. > Thus M times more data is read. > I totally agree with the rationale. How realistic this simple estimate is, I agree (as you imply below) depends on the application. > But it depends on expected value of N. If it is low (e.g N*M<1) then query > time will be dominated by search but not data read or transfer. So it > doesn't matter in this case. > But if you queries you run typically return many instances it might be a > problem. You mean many instances of the subclasses dont you? _______________________________________________ > elephant-devel site list > elephant-devel@common-lisp.net > http://common-lisp.net/mailman/listinfo/elephant-devel >
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