bbs bump ordered index

I'm making a BBS thing without using sql and I'm wondering what's the best way to save the bump order
I'm thinking of having a array-like index that each line has the thread-id but if someone bumps the last thread it has to move everything one line down and insert the last line into the first line
do you have any other way to save the index? how does shiichan/tablecat/non-sql forums/4chan do it?

What is your adversity to using a filesystem? Why are you trying to make things harder for yourself?

>>20
Isn't a file system a form of nosql db after all?