[elephant-devel] Querying for objects on two slots

[Robert Synnott]

I don't believe the Postmodern backend, at least, allows search by conses.

If you want sensible (ordered) results with a and b if a and/or b are
integers, by the way, you should zero-pad them; otherwise, say, '1 2'
comes after '1 12', which is probably not what you want
Rob

2009/1/14 Yarek Kowalik <yarek.kowalik at gmail.com>:
> 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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>
>
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Robert Synnott
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