I updated all the packages I installed with Homebrew. MySQL got upgraded to 5.6.12 (from 5.5.27 or so):
$ mysql --version mysql Ver 14.14 Distrib 5.6.12, fo
The top answer here is out-of-date... the brewers have fixed mysql:
brew update brew upgrade mysql gem install mysql2
This will update mysql to the latest version, which seems to work fine with the mysql2 gem on OSX.