so I finally managed to create the scene for reproducing memory issues...
Basicaly it doesn't matter how big the scene is, it always happens when you want to make a close-up shot on an object in a bigger scene/environment.
here's the scene:
testscene_closeup.rar
Sometimes it helps to tweak the parameters(map resolution) in other cases it worn't help and it can even introduce artifacts if clamping is used.
I would sum up my experience with this feature like this:
Pros:
1. Automatic (almost)
2. Performance boost - in an ideal condition it will perform just as good as portals. (fewer openings, not too many objects in a scene and no close ups and no border rendering on previews)
Cons:
1. None of my production scenes fit the "ideal conditions" and I doubt anyone who would use luxcore for professional use would have a smooth experince with this feature.
2. It's painfully slow and makes previewing complex interior renderings impossible - many times I wait longer on preprocess than on the preview render itself
3. It's unpredictable. I don't know if I'll have enough memory until I do rendering, then if I run out of memory it takes forever for luxcore to figure out it won't fit into vram and then I can try lowering resolution and hope that I will see some rendering done.
4. It's unreliable, in some cases I can get clean and fast rendering using pretty low clamping values, however artifacts from this cache might creep in
renderings and sometimes they are so subtle that I might only notice them a good amount of time in rendering.
5. It's not really an automatic solution, it cannot be used all the time as it will damage performance in open scenes (now you might think, ok but why would you use it in an open scene? Well 3 times already I worked with an interior that had so many openings that this cache was pretty much useless and only added to rendertime with preprocessing)
So all in all, when it works it works well, but I have no time figuring out if it will work and how well it will work during a project.