3Delight rendering slows down over time

genius_3587271

I have observed some unexpected behaviour. I have a work around, so this is more for academic interest than anything else.

Normally, when I set off an image sequence render, I can measure the "time per frame" at the start, and from that work out roughly when it will finish. But not with my latest scene. This latest one takes twice as long per frame after about 5 hours; 3 times as long after about 14 hours. The work around is simple - stop the render, shutdown & restart Daz Studio & restart from where I left off - so that is what I am doing every few hours.

By removing items in turn, I've worked out the culprit is the oumua figure.

Another observation which may give a clue as to what is going on. The rendering progress bar stays at 0% for some time, before then ramping up to 100%. It is the period stuck at 0% which appears to increase over time. Also, when stuck at 0%, the machine is barely using any CPU and the majority of cores are sleeping. Once the progress bar starts moving it's virtually 100% CPU & all cores are in use. With all of my previous scenes I barely notice any delay before the progress bar starts moving. From this I assume there are distinct stages to the rendering of an image: some sort of preparation phase (which I assume is single threaded & what is, for some reason, increasing over time); followed by the actual render itself where all available cores are used. If I'm right about this then this "preparation" phase must be significantly extended when the oumua figure is included.

So, just to satisfy my curiosity, any idea why this is happening?