[elephant-devel] Re: Getting count of the number of persistent objectsof a particular class

[Alex Mizrahi]

 JN> I did some reading through the mailing list archives and the Elephant
 JN> manual, but cannot find a recommended way of counting the number of
 JN> persistent objects of a particular class.

 JN> I have a method that works (using map-class) but this is way too slow
 JN> for my purposes.

 JN> I did find some postings from Oct last year about this question but no
 JN> definitive answer it seams.

 JN> Any advice?

as far as i know, most btree implementation do not have a fast way to count 
leafs -- you need to iterate through all of them.
in PostgreSQL (and i think in most relational databases like that) query 
"SELECT COUNT(*) FROM tree11" takes time proportional to number of elements 
in tree11.
of course it would be much faster to do "SELECT COUNT(*)" then reading all 
elements on Lisp side, but it will be flawed anyway.

so, the advice would be to count this parameter yourself. for example, make 
btree class-name -> instance count. and update it in initialize-instance 
(you can move this functionality to some instance-counter-mixin class), and 
whereever you delete them..