Code Reading: The Open Source Perspective (v. 1)

Start by reading Redis code, slowly take notes on paper, try to make your version changing small bits at a time.

https://www.amazon.com/Code-Reading-Open-Source-Perspective/...

"Code Reading" tends to be criticized, but I think mostly unfairly.

I just skimmed the article, but a more comprehensive text on acquiring the skill to read code is the book Code Reading, from Diomedis Spinelli [1].

[1]: https://www.amazon.com/Code-Reading-Open-Source-Perspective/...