As we all know, DataContext doesn't clean up unused registered
objects on an assumption that the entire DataContext has a finite
lifespan and will be garbage-collected eventually.
In my session-less web application I am using an app-scoped read-only
DC shared by all requests. Sure enough it leaks memory, given a big
enough database. In the past we solved this problem by periodically
replacing a shared instance of DC with a new one. Since this approach
intrerfered with the caching mechanism and generally seemed dirty,
the other day I implemented a self-cleaning ObjectStore based on
commons-collections ReferenceMap:
class LeakFreeObjectStore extends ObjectStore {
public LeakFreeObjectStore(DataRowStore dataRowCache) {
super(dataRowCache);
objectMap = new ReferenceMap(AbstractReferenceMap.HARD,
AbstractReferenceMap.WEAK);
}
}
Note that I couldn't use LRUMap, as we can't unregister objects that
are referenced by other application objects, so instead I used weak
references to cleanup otherwise unreferenced instances. Been watching
this in production for a day and it works perfectly.
Now the question is whether we want this behavior as a default (or as
an option) for the DataContext? In other words should I move this fix
to Cayenne? (I will have to modify it to create hard references to
the dirty objects as we can't deallocate those even if they are not
referenced in the app).
I'd say yes, but I was wondering if premature garbage collection of
registered objects is bad for any reason? Thoughts?
Andrus
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