darktable's thumbnail cache: where the mipmaps go on a Mac, and how to cap them

darktable creates thumbnails, called mipmaps, for every image it shows in the lighttable, at several sizes, so browsing is fast. Its documentation puts the cache in ~/.cache/darktable, the same place on a Mac as on Linux. It is easy to miss on a Mac, because few Mac apps use that folder.

Measure it

du -sh ~/.cache/darktable
du -sh ~/.cache/darktable/* 2>/dev/null | sort -h

The thumbnails are in folders named mipmaps- followed by an identifier, one per library. Precompiled graphics code is cached there too.

Clearing it

darktable's manual describes clearing the thumbnail cache by deleting the files in the mipmaps-*.d folder. Quit darktable first. Thumbnails are regenerated as you browse, which is slow the first time through a large collection.

rm -rf ~/.cache/darktable/mipmaps-*.d/*     # with darktable closed

Choosing how big it can get

• The in-memory cache size is set in Preferences, CPU / GPU / memory.
• Generating thumbnails in advance for a whole collection fills the disk cache quickly. Do it for the folders you are actively working on rather than your whole archive.
• If you use several libraries, each has its own mipmaps folder. Clear the ones for libraries you no longer use.

Where the real space is

darktable edits are stored in small sidecar files and its library database, which stay small. The space in a photo workflow is the raw files themselves. See Mac storage for photographers and RAW plus JPEG, and for other editors, photo editor caches.