Did you see this discussion? https://news.ycombinator.com/item?id=32965075
As far as books are concerend: - Database Internals
- Designing Data Intensive Applications
- Disk-Based Algorithms for Big Data
- Database Systems by Ullman et al (http://infolab.stanford.edu/~ullman/pub/dscbtoc.txt) Part IV covers implementation details of a database system.