Thumbnailing is slow
I thought Nautilus' thumbnail generation speed was just "normal" or somehow limited by the speed of the gnome thumbnailer libraries, so I never paid attention to it... until now, where I discovered it's actually comparatively slow. Very, very slow.
If I grab a folder with 106 JPEG images totalling 1 gigabyte (fairly big images at ~10-12 MB each) as a torture test, or the contents of one of the subfolders in /usr/share/icons, and pit Nautilus against XFCE's "Thunar" file browser, Thunar absolutely crushes Nautilus. With Thor's hammer.
Clearing ~/.cache/thumbnails/ between both benchmarks, thumbnailing my "big picture folder" yielded the following results:
- Nautilus: 28.82 seconds.
- Thunar: 1.30 seconds.
The Thunar numbers are not a typo, it really is over 20 times faster than Nautilus (where you can see each image being painfully thumbnailed one after another). My thumb was barely fast enough to stop the stopwatch in Thunar's case. I don't know how Thunar does this, but you need to steal their code.
This is on a SSD and an 8-cores Xeon processor on Fedora, but I've seen the same thing happen on my friend's computer running the latest Ubuntu.
Update: see also this list of thumbnails-related performance issues.