[rules-users] Garbage collection in working memory

I read with interest how Drools 5 Fusion is able to compute when facts can not longer activate anything, and garbage collects them. Very clever and elegant! I am contemplating long-lived stateful working memories in a Drools 4 application. I assume that if I modify a fact, a new copy replaces the old copy, and the old copy should be subject to Java garbage collection. No net memory leak. If I add a new fact, use it, am now done with it, neither Drools nor Java knows it is collectible. If I have a rule like "When A and B...", I may know the B event is completely dead, but Drools can't know if a new A will arrive and use the B event in the activation. What is the state of the practice for managing working memory for Drools Expert applications? * Do people write rules to manually delete facts when they are no longer needed? * Is Drools smarter than I know, and is able to do the garbage collection of facts for itself? * I gather one common option is to limit the lifetime of the session, to do the nuclear garbage collection by killing the session and starting a new one. That could be a lot of hassle here, there are no good stopping points. I'd have to figure out what events need to be transferred over into the new session. Various people obviously run very large Drools apps but I have not seen much discussion of this issue. I am hoping there is something obvious I am missing, so I don't have to write an application-level fact collector myself. thanks, Allan