I've got a pretty powerful system and I'm an animator / cartoonist by trade. I have thousands upon thousands of images on my PC, and I find myself in 2020 often waiting to browse a folder in thumbnails mode, while the computer again updates the thumbnail images. I've got the appropriate Windows tweaks set to increase the thumbnail cache, keep the maintenance from deleting that cache as well as just now increasing Opus' cache for such things.
Is there any way to have Opus do a one time massive pass through every existing drive / folder on my pc and just generate thumbnails for absolutely everything? I wouldn't care if it took a week to complete.
I don't think there is a good way to do that currently.
Something which may help slightly is Auto-load Thumbnails only in specific folders which you can use to make Opus start pre-caching thumbnails as soon as you enter a folder, even if you haven't switched to thumbnails yet. But you'd still need to enter a folder for its thumbnails to start generating.
In the thumbnail cache setting, there is a "use loseless compression". Does checking that increase the size of the cache but will speed up the thumbnails loading?
There is also a "Thumbnails threads" which defaults to 12. I am guessing setting it to 24, will speed things up too, maybe?
Lossless compression won't speed things up. It's more of a space/quality trade-off than to do with speed.
The number of thumbnail threads defaults to the number of threads your CPU has (up to a maximum where adding more threads probably won't help because storage becomes the bottleneck). If it is defaulted to 12, you presumably have a CPU with 12 threads. Increasing it to 24 would probably slow things down in that case, but you can try it and measure the results if you want to test the idea.
I faced a similar problem some years ago. To solve it, unfortunately, took a lot of work.
First your need a decent directory structure to keep the number of images to be thumbnailed in any folder to a reasonable number. (An alphabetically schema is a sound starting point)
Next, if you use a lot of graphic formats like PDF Adobe Illustrator of EPS files, then you also need a decent thumbnail generator.
Next you need to add appropriate metadata to your files and index them with Windows 10. That is the killer, as backdating metadata is tremendously time-consuming.
Add appropriate Opus tab groups to get around your directory schema efficiently, and there should be no reason why you cannot find the image you want in under a couple of seconds.
Only you can know whether the task is worth the effort.
Trying to make thumbnailing keep pace with your needs is, in my opinion, a dead duck.
I might be wrong, but OTOH it should be possible to just use the Flat View in "Mixed (No Folders)" mode and turn on the thumbnails view, that should generate the thumbnails of all files in the current folder and its subfolders.
If Opus doesn't generate the thumbnails for files which are not in view, you'll need to scroll the large file list manually of course, but still better than having to navigate folders in & out.
Pro tip
Enter this path: /dopuslocaldata/Thumbnail Cache to see the thumbnail cache database files, you can see by their date (and existence) whether the Opus generates any new thumbnail cache files.
For the large amount of files the Opus lister will hang until the Flat View processes everything so patience will be needed.
I think Flat View only generates thumbnails that are visible (plus an extra row so they're ready before you scroll). Running Show LOADALLTHUMBS might force Flat View to generate everything (not sure). But it would be very slow just to load a huge folder, and could potentially use a lot of memory (or cause some of the out-of-view thumbnail requests to be dropped once memory usage gets too high; I forget the exact strategy).
Caching usually takes care of itself. Maybe a better thing to look at is why generating uncached thumbnails is so slow. It would usually be very fast, unless the images are huge or the storage/network is slow, or antivirus is delaying files being loaded, or archives are involved, or file formats which Opus doesn't handle natively (in which case caching them via Windows will work). There may be things to look into there instead.
@leo True, the reported slowness itself is weird, there shouldn't be need for any preloading hacks. I've tested and thumbnails get generated instantly for thousands of jpg files (I've made sure to clear the cache).
@cartoonmonkey I think the slowness problem might be due to a complex filetypes (PSD with some complex features/effects/smart layers or maybe vector image filetype?), large image resolutions and slow third party thumbnails handler.