All buckets hanging on start of render

[lukepenry]

I am facing a problem that I cannot work out. When I hit render, the scene loads and then starts “rendering” but the buckets hang for a very long time at the start of the render, and then take off all at once and render as they should.

I am testing this on a small number of objects, but when the scene is full it can really take a long time.

My scene is lots of XRefs scattered with forest pack. I have been in contact with the forest pack team and been running tests to determine if its that causing the problem and it looks like it’s not, because if I replace all the forest pack scatters with instances it still happens. It seems to be an Xref thing, but I can’t work out what Xrefs and Vray have to do with one another.
I just finished rendering on a cloud farm and was told by their staff that some frames took 2 hours before starting the render.

I have attached a real time video of a smaller test scene to view so hopefully that helps.
https://www.dropbox.com/s/wi1iuw0rjz...15-28.mp4?dl=0

About 40 Xref animated objects. Xref file is 2gb

Specs:
AMD 32 Core threadripper
3080ti
128gb Ram

[^Lele^]

There are a number of things that can happen as the frame starts being rendered.
Proxies start getting loaded, dynamic displacement and subdivisions are calculated, and so on.
If those are in xRefs, the loading compounds, sometimes in unfathomable ways: a displacement setting that was good for the xRef when that was tested alone, may change into an untreatable problem as that asset is xrefed in the final scene (change of resolution, screen coverage, and so on.).

Have a read here as to the general concepts about RAM reduction, as it also contains some of the pitfalls of using those techniques.

[lukepenry]

thanks for the speedy response, I had read this a few weeks ago and it was very helpful although none of it seems to fix this issue.

there is only displacement on 1 surface and none of the XRefs. the xrefs are simply animated by point cloud data files. could they perhaps be the issue?

[^Lele^]

Umh, it ought to be loaded before the frame start, so to pass V-Ray the correct vertices positions.
If you could pack the scene and send it to support (the full thing would be ideal), then we may be able to investigate what the exact issue is.

[lukepenry]

It's over 100gb and i don't have time to do that, sorry. thanks though. I will keep trying some stuff or just live with it.

[^Lele^]

Well, try and merge all xRefs, and see if it works any better.

[lukepenry]

It doesn't seem to change anything, now i'm confused lol

[lukepenry]

After some more testing the problem simply seems to be having to load lots of geometry, I thought using Xrefs and Forestpack would stop this type of thing from happening, but i guess there is no way around it sometimes.

[^Lele^]

Eh, no, sometimes it's just brute-forcing the heck out of it.
Don't feel alone, though.

[lukepenry]

Although i can't use Vray GPU for this project as some features are not supported i am interested to know why this hanging doesn't happen when I use it, it doesn't even seem to load any textures, just starts rendering.

[^Lele^]

Possibly some feature is different, or unsupported, of those you use.
Impossible to say from here.