Debugging MySQL installed through Homebrew on Yosemite

I recently came across an annoying issue where MySQL would not start on Mac OS X Yosemite, exiting with the following:

ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)

Join me on a journey which makes putting a greased ape on a waltzer and getting him to rate the experience seem like an easy task.

Finding the log files

To fix what’s going wrong, we need to know what’s going wrong. Unfortunately, finding log files (for me at least) can often be a bigger job than fixing the issue at hand. My version of MySQL is installed through Brew. After six days of Googling, I eventually found MySQL’s error log here:

tail -f /usr/local/var/mysql/Daves-MacBook-Pro.local.err

Four and a half days trawling through something which makes War and Peace look like a children’s book, I stumbled on a possible cause for the error:

2015-11-12T15:35:05.354808Z 0 [Warning] InnoDB: Ignoring tablespace `defender/wishlist_item_option` because it could not be opened.

Aha! It looks like one of the databases has become corrupted, MySQL can't open it, and it's failing! Great. Let's try moving the database elsewhere and see how we get on.

ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)

No dice. Right, looking through the log shows up another error:

2015-11-12T15:48:13.051616Z 0 [ERROR] unknown variable 'key_buffer=32M'

Variable variables

So, it looks like the variable key_buffer has been replaced with key_buffer_size in a newer version of MySQL. This exists in my MySQL config file:

/usr/local/etc/my.cnf

Changing this sorted my headache, and allowed me to get back to those yummy scrummy databases once more.