As I try to re-import my photo for renaming all my photo file to unique name. I found that if my library growing large, the import time increase significantly.
When the library have 183,000 photo, 128 photo required 1m53s to import.
So, I remove the library.db to test an empty library, the same 128 photo just need 4s to import.
For 10K photo import, it will take about 2~3 hours to complete.
I am running Darktable 3.4 on Windows 10, AMD 2700X, 32G ram. The CPU / DISK usage keeping low during import.