[elephant-devel] Getting count of the number of persistent objects of a particular class

[Ian Eslick]

Part of the problem with Elephant is that we currently create CLOS  
objects in memory for every 'row' that is touched in a query (or  
touched during an index operation).  We have to de-serialize the  
record, create an object, initialize any transient slots, etc.  The  
SQL engine, by contrast, can just keep track of a list of OIDs and  
then count the size of the arrays that result from any joins.  This is  
a much cheaper set of operations per-row (i.e. per object).  If we  
only read OIDs into memory until the final step when we need to access  
a slot, we can save quite a bit of the cost of object creation.

My hope is that a query system would implement this model properly.   
Unfortunately, this will not happen soon, as much as I'm itching to do  
it!

However, the recent change to split object instantiation into initial  
and deserialization pathways should have sped things up a bit (e.g. no  
p-slot accesses during de-serialization).

Ian



On Jan 20, 2008, at 9:32 PM, Joubert Nel wrote:

> Hello,
>
> I did some reading through the mailing list archives and the Elephant
> manual, but cannot find a recommended way of counting the number of
> persistent objects of a particular class.
>
> I have a method that works (using map-class) but this is way too slow
> for my purposes.
>
> I did find some postings from Oct last year about this question but no
> definitive answer it seams.
>
> Any advice?
>
> Joubert
>
> PS: I'm using the postmodern back-end.
>
>
>
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