The only solution for me was to learn some database internals (I read the wonderful book written by Alex Petrov), and the problems seemed so interesting, I could not fight the urge and went ahead with trying to write my own db.
Anyway, ~9 months have passed and I feel like I'm "done", I have learned a ton, and really proud of dbeel.
Now I can pick a database and way more easily understand what are its most defining traits.
Some short time in the future, I will release a blog post or something, where I will write about the fundamental problems you need to solve when writing a performant data system like a database, so stay tuned :)