Transactions, really? How do you lock rows, how do you have relations, how do you do joins? In fact, ext3 can only handle about 50,000 files in one directory. So you'll have to split up your "primary key" into letters like abc/def/foo like we do
The bad but valid answer to locking rows and doing relations is that you write the logic in to your application. The better answer is of course that if you’re doing specific types of complex things a DB is a better fit.
Honestly splitting in to nested subfolders is not big deal anymore, it’s a single function you can write even if you’re having a “.10X” day.
