Jupyterhub: Jupyterhub 0.7.2 does not work with a MySQL backend

[yuvipanda]

How to reproduce the issue

1. Setup a JupyterHub with mysql database backend, pointing to an empty database

What you expected to happen

1. JupyterHub creates the required tables in the database on start

What actually happens

It fails to start, with:

    sqlalchemy.exc.InternalError: (pymysql.err.InternalError) (1071, 'Specified key was too long; max key length is 767 bytes') [SQL: '\nCREATE TABLE groups (\n\tid INTEGER NOT NULL AUTO_INCREMENT, \n\tname VARCHAR(1023), \n\tPRIMARY KEY (id), \n\tUNIQUE (name)\n)\n\n']

I think the group name needs to be smaller.

[ckbhatt]

Adding following to my.cnf
innodb_file_format = Barracuda
innodb_file_per_table = 1
innodb_large_prefix
and restarting MySQL changes allowed length and works as a workaround for now