Ask HN: Resources for creating my own database

I know a lot about to how use different databases (SQL, Elasticsearch, Mongodb, etc), but I thought it would make an interesting project to create my own database. I have an idea of where I would start, but was hoping looking for some resources to help me out (free or paid). I tried googling around but most of the results are dominated by MS Access or SQL stuff.

Any links to books/pdfs/github repos would be awesome.