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?

>>29
most file systems have all the things that needed in a database and it's really easy to use, one way is to use it as a key-value database (file path + name = key, file = value) and having hard/solf links for many keys with one value
with file systems like the apple's one you can do even more things