Very slow DB regenerate

I had to learn this the hard way too. Never, ever manually delete (or add, or modify) files in Blue Iris managed folders. It's a certainty that this will damage Blue Iris' fragile database. At this point, I would:
1. Close the Blue Iris app.
2. Stop the Blue Iris service.
3. Delete the *.db files in the database folder.
4. Reboot.
5. Start Blue Iris and let it regenerate the database.
This makes sense. I suspect if one deletes the .dat files in the Managed folders, the DB needs to to regenerated from scratch.
I suspect that I didn't have the hanging issue because I had already tried 'Delete and Regenerate' which had also failed to complete, and I did the regenerate (that completed successfully) without restarting BI.