FreeBSD does not automatically include a default my.cnf for MySQL. Instead, a set of sample configuration files can be found under /usr/local/share/mysql. These configuration files include my-small.cnf, my-medium.cnf, my-large.cnf, my-innodb-heavy-4G, and my-huge.cnf. The appropriate file can be copied and used as a template configuration by performing the following actions:
cd /usr/local/share/mysql/
cp /usr/local/share/mysq/mysql-large.cnf /etc/my.cnf
/usr/local/etc/rc.d/mysql-server restart

thanks to http://www.barik.net/archive/2008/05/26/114616/ for the tip.