From KDE UserBase Wiki

Optimise digiKam’s Performance

Transcribed from Mohamed Malik's web post of 21 February 2011

There are a few things that you can do in order to optimise the performance of digiKam when you are using it for the first time.

1. Rebuild All Thumbnails...
When digiKam starts it loads the thumbnails whenever an album is opened. Most of the time this takes sometime, however you can solve this issue by generating thumbnails. To do this go to Tools -> Rebuild All Thumbnails. Depending on the amount of images on your collection this will take sometime.
2. Rebuild All Fingerprints...
This option is a must if you want to search your images for duplicates or if you want to enable fuzzy searches. To do this go to Tools -> Rebuild Finger Prints.
3. Scan for new items at startup (makes startup slower)
By default digiKam scans your collections for new images. If you feel digiKam opens slowly when starting up disable this option. To do this go to Settings -> Configure digiKam. When the window opens go to the last option on the Miscellaneous screen and disable it. See screen capture below.

These options will definitely improve performance and will give you a much more pleasant experience with digiKam.