Apart from using Cloud SQL, I haven’t touched MySQL for a while, so I decided to freshen up things and read High Performance MySQL by Baron Schwartz, Peter Zaitsev, and Vadim Tkachenko. The book feels solid, it explains how MySQL works (and worked before) inside, what problems storage engines/parser/optimizer/etc have and how to leverage them. It’s kind of nice that a big part of the book is about MySQL scaling. And it’s also good that the book has a lot of information about troubleshooting, debugging, profiling and some MySQL related tools.
Although the book is probably a bit outdated, it covers MySQL versions up to 5.5, but nowadays the latest version is 5.7.