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I have a fairly complex scene which is consistently crashing or glitching out my system:

Ryzen 2700X 32 Gb RAM, RTX 2060, 90 Gb Swap file. Linux Ubuntu.

I am using Blender 2.90.1 but this was occurring in earlier versions.

I have had to increase the swap file on my system, and the amount of memory the scene is using when trying to render in Eevee is 90 Gb...I just don't understand it. It's big but not that big.

By contrast rendering in Cycles (BPT) is only using 20 Gb, and renders without issue, other than it takes a long time.

The main culprit seems to be a character that has UDIM textures, but the rest of the scene is using "way too much memory" as well. I have been able to render the scene in the past but only just, and it often has glitches. There is enough swap memory to allow the scene to render in theory, but I seem to now have pushed it over the edge.

I don't understand why Eevee requires so much memory to render but cycles does not. Can someone explain?

DrIgnatiusCole
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    Suggest try to render using the command line: https://docs.blender.org/manual/en/latest/advanced/command_line/arguments.html – brockmann Nov 21 '20 at 18:15
  • Thanks for the suggestion but I am not sure how this would help. It would also be useful to know how to use command line to start renders...the document doesn't explain. – DrIgnatiusCole Nov 22 '20 at 11:32
  • Helps reducing memory usage: https://blender.stackexchange.com/a/16261/31447 Also, how to render using the command line is explained in the link I've posted (note: there are hundreds of great answers here explaining that as well) – brockmann Nov 22 '20 at 11:44
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    Thank you again for your comment. For those struggling with the rather cryptic and lack of information on how to do this, you need to: 1) Open terminal 2) type in "blender -b" without the quotes, then a space. Drag the file you want to have rendered into the terminal at the location after the word "blender". This will locate the file you want rendered. 3) type a space and then "-a"...without the quotes. The instructions given elswhere are very confusing. The documentation on command line rendering can be found here: https://docs.blender.org/manual/en/latest/advanced/command_line/render.html – DrIgnatiusCole Nov 23 '20 at 15:32
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    Update: I was able to get the render to start but it is using Cycles render, not Eevee. According to the documentation: "Render the whole animation using all the settings saved in the blend-file.", but it is not rendering in Eevee. It may be possible to use "-E EEVEE" by adding that before "-a". – DrIgnatiusCole Nov 23 '20 at 16:16
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    Update 2: That should be "BLENDER_EEVEE". Also, I allowed the original render to render 1 frame with what must have been cycles (though I don't know whether it did in BPT or normal PT mode), but I don't know where blender saved it. It is not in my output location. – DrIgnatiusCole Nov 23 '20 at 16:39
  • Eevee is still using too much memory. Using command line render made no difference - it was still using about 90 Gbs compared to Cycles which using less than 30. However it did help to render a few frames - it managed 18 of the 500 I am trying to render before crashing, but unfortunately those frames are also glitching. Does anyone have any other ideas? Why is Eevee using so much more memory than Cycles? – DrIgnatiusCole Nov 24 '20 at 09:11
  • Update 3: This computer has been upgraded to a 2070 Super and this APPEARS to be rendering - though I won't know if it is without glitches because I stupidly decided to render as mp4 instead of image sequence. It still doesn't explain why Eevee is taking so much more memory than Cycles, but at least it is worth mentioning that 6 Gb card may not be enough for big scenes. – DrIgnatiusCole Nov 24 '20 at 21:43

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