Check the reviews online, but generally random bits of Go code are presented with no build-up or explanation. B Trees are implemented immediately and without explanation. The book is incredibly short and seems just like a loose collection of notes, rather than an actual book. Very interested to check out the new version
https://leanpub.com/build_your_own_database_from_scratch/c/L...
To be honest it seems a bit strange to pay for the code since all the source codes to build the database is literally inside the book.