Ram usage and previews

I'm new to Fusion and I wanted to learn it because i find nodes much easier to handle than levels. But I have a problem and I can't use this software at all. Previews are really slow and I think the problem is ram management. It is true that I have only 8 GB of ram, but It's strange that a short 60fps 1080p clip makes my ram full, Fusion starts to lag and I have to force quit everything; this without any effect. When I use After Effects, very often previews aren't real time, but with ram cache, waiting a bit, I can see the final result. Instead in Fusion, I start the preview and for a few seconds it is realtime, then it start to slow down until the ram is full and everything is unusable. Can anyone explain me how to improve the cache management (If this is the problem)?
In the preferences I tried to put some limits but they seem not to work. I also wanted to know if OpenCL is worth it or not.
Thanks.
P.S. sorry but I'm not English so I could have done some mistake.

Hey Giulio,

sorry to hear that Fusion is not working for You as expected. However 8GB is really low by Fusion standards, and a big chunk of it will be already used up by Your operating system and any loaded apps. Even simple comps will max out the rest of it pretty fast, as You already noticed.

You can try enabling the disk cache for certain nodes and prerender Your comp until that particular node. Check out this post https://forum.blackmagicdesign.com/viewtopic.php?f=22&t=63561. There is also this (old) video which explains caching pretty well

. I am not sure if a lot (or anything) has changed since then, and I think it is a good starting point.

Hope this helps,
Marin

Hello,
Thanks for your answer. I know 8GB are not so much, in fact I was not expecting real time, but I wanted only fusion to run smoothly, at least like After Effects does. I will check what you suggested and I will let you know the results.
Thank again

Hello, I tried every possible ram, ram cache, disk cache and OpenCL setup, after a preview or a few nodes Fusion fills all the ram and my OS seems to crash, it can't load the desktop wallpaper for how it is charged. At this point I think Fusion is not optimised at all for my system. When I started using after effects I was complaining how bad it was for previews and general speed since for example in motion I can have effects in real time on 4k clips and the same on Final Cut. Watching same video I discovered that DaVinci Resolve was also optimised with Metal to have similar performances to Final Cut and so i thought that it would have been the same for Fusion but it isn't. Obviously I cannot use Motion for VFX, a lot of tool there are missing such as camera tracking, rotoscoping tools and all the plugins. It seems that After Effects for now is my only choice.
Thank you.