[elephant-devel] Querying for objects on two slots

[Yarek Kowalik]

When serializing tuples, is the string representation best:  You suggest
using (format t "~A ~A" a b) - is that efficient enough?  what about doing
(cons a b) = is there a way to index and search for conses? Any other ideas?

Yarek

On Tue, Jan 6, 2009 at 5:17 AM, Alex Mizrahi <killerstorm at newmail.ru> wrote:

> YK> Is this a reasonable way of finding an object of type
> YK> 'my-class that matches on values val-a and val-b for slots a and b?
>
> yep, it is reasonable if you have relatively low number of objects
> in returned by (get-instances-by-value 'my-class 'slot-b val-b) query.
> if number of objects is significant and you get a slowdown because
> of this, you might want to optimize this. a trivial thing is to try it
> symmertrically with slot-a -- whatever returns less objects is better.
> less trivial optimizations would be to work on lower-level -- via
> map-inverted-index (to avoid allocating whole list but instead test objects
> one by one) or even cursor API (this way you can retrieve oids rather
> than objects, which should be faster, and also iterating both indices at
> once might be a significant benefit if values are not uniformly
> distributed).
>
> but the most optimal way doing this in case of high number of objects
> in both slot-a and slot-b queries would be building and using multi-column
> index. unfortunately, Elephant does not help you with it -- either you'll
> have
> to serialize slot tuples into a string (e.g (format nil "~a_~a" slot-a
> slot-b)),
> or reorganize your data to use a custom index structure (like btree of
> btrees).
>
> there are also backend-specific considerations. for postmodern
>
>  (intersection (get-instances-by-value 'my-class 'slot-b val-b)
>                    (get-instances-by-value 'my-class 'slot-a val-a))
>
> would be much faster then testing objects one by one, for BDB -- i doubt
> so.
>
> LP> Use MAP-CLASS, this will considerably speed up the query.
>
> how is that? using at least one index is much better than using no index at
> all.
>
>
>
>
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