[merijnv]

> Is making à file based database that hard,compared to creating new programming language for exemple ?

Yes. I can hack together a trivial compiler in a weekend. A serious (non-optimising) compiler for a complex language is a task you could do in a few months.

If you gave me two year I'm not sure I could implement a filesystem API that correctly did something as simple as "atomically append to a file". See also Dan Luu's writing on the topic of filesystems: https://danluu.com/deconstruct-files/