We have a lot of documents in our folders and there is no need to generate tiny images as it is really slow and pins all 16 cores to 100% as users scroll.
We want to keep this feature for Image thumbnails (png, jpg). I just can’t figure out how to do this…
I know we can pre-generate thumbs, but I don’t want the user to need to load the images at all. The default icons are far better
This disables PDF but also everything else: 'enable_previews' => false
This disables images but PDF and other documents still generates thumbnails: 'enabledPreviewProviders' => 
I’ve gone as far as to edit ImageMagic’s meta.xml and removed PDF from the meta and it still generates thumbnails.
How do I disable document thumbnails? Ripping my hair out here
1200-1800ms for the previews to load, and it pins the CPUs. At the moment we only have IT trialing it with 3 users. If more users come online, I’m afraid that the previews will slow everything down during peak times.
Although if accessing already generated previews, it loads from cache, we have hundreds of folders of PDF invoices and other documents that will be accessed at one time.
As for the preview generator, I have tried that out, but it only uses a single core and is very slow to generate previews. I read in the issues that some people run it for 18 hours and still going.
Just had a look and mem is actually unrelated. mysqld and snapd
This will save you CPU time in peak hours. Just execute it at the evening to be ready for a next day.
You can always interrupt it and as you say, it uses only 1 Core, should not be too bad for your performance.
For my old 2 core Cubietruck
For my new Ryzen with 16 GB RAM around 6 Hours for the same amount of job after migration to the newer Server.
Even after I moved out Preview folder to the SSD, by simply mounting it to the nextcloud folder as preview app, now All Nextcloud files are on a huge HDDs, but previews are on a SSD that makes random access to them extremely good.
mount | grep preview
/var/previews on /mnt/raid/nextcloud/data/appdata_xxxxxxxxxxx/preview type ext4 (rw,relatime)
I guess this is the solution for now as I don’t have time to try to replicate this issue and submit to github. I’m 80% sure its to do with preview requests being sent to Collabora when it shouldn’t have been.
Would be nice if it can run in parallel. I will try this weekend when no one is using the server in case it rolls over to the next day.