Databases are not black boxes. Understand them by coding your own from scratch!
A walkthrough of a minimal persistent database implementation. We start with a B-Tree, then add a new concept with each chapter, and eventually go from a simple KV to a mini relational DB.
Covers three important topics:
1. Persistence. How not to lose or corrupt your data. Recovering from a crash.
2. Indexing. Efficiently querying and manipulating your data. (B-tree).
3. Concurrency. How to handle multiple (large number of) clients. And transactions.

Ever wondered how computers turn source code into working software? You can learn the art by building your own mini-compiler.
A succinct book walks through a minimal yet complete compiler implementation. Compiles a static-typed language into x64 ELF executables.