I agree with you. The Raytrace engine seems to handle gpu ram rather poorly and I don´t understand why it is requiring so much computer power compared to any other ray-trace engine I came across in any 3d software. I have recently finished a project were I used the ray-trace engine a lot - and I had to reboot my machine more than I´ve ever done before (like 5-10 times a day). If I did as much as look at a website, chances were the render would crash and give me the cryptic message of 5070. And upping the sampling from 3 was just too risky, so the final result became more grainy than what I would have hoped for. And changing to CPU render would make the ray trace engine unusably slow. So, with the extremely limited possibilities with the ray trace engine compared to f.example Element 3d and considering how much VRAM it needs the whole engine seems to me as being unfinished and badly optimized. I think I will invest in Element 3D, its performing faster and giving a better result anyway and you have much more options. ..Adobe should give us the option to purge the GPU RAM in AE until they improved the code, so we would be able to multitask without rebooting EVERY time doing anything else than AE on the machine.
As for specs, I thought I bought a good machine last december when I bought a fully specced iMac late 2012, with a 680MX with 2gb VRAM.... But obviously thats far from ok specs according to what Adobe expect AE users to have for the GPU . That leaves the new unavailable Mac Pro the only option for Mac Users wanting to use the AE ray trace engine efficiently without trouble while still multitasking. That´s a bit disappointing, I hope it will get better over time
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The After Effects CC (12.2) update and After Effects CS6 (11.0.4) update include fixes and changes regarding the OptiX library for the ray-traced 3D renderer that make VRAM handling better, prevent crashes, and otherwise improve the experience in this area.
Let us know how it's working for you after you've installed the updates.