Thanks I understand now. It is quite clear.

In my case however, the accumulated Foo's will be different for each source Foo. The two classes could have been different. A more precise sample conditions would be :

$a: A(someConditions)

accumulate ($b:B(someField==$a.somefield); ....)

My problem being that the Drools engine will create one RightTuple per instance of B (and per rule with a similar accumulate), even if no instance of A matches the someConditions.

I will try to add alpha conditions (not related to $a or other CI) to $b, to reduce the number of joinable instances, but it would be great to be able to ask drools to wait for the $a to match before looking for the $b's. Was'nt it something that Phreak enabled ?

And about the diagnostic function, listing the most numerous Tuples. Does a similar it exist somewhere? If not do you think it could help others ? It sure helps me finding the related conditions.

Regards,

Benoît