I've been involved in a number of interviews over the last few weeks as a client has been loking for a MySQL DBA. When you are looking for position as a DBA in a large scale environement there are some very important things you have to know.
You absolutely must know a scripting language. In a smaller environment this often isn't necessary. You will live and die by this in a large environment. I asked every applicant one specific question..if you had to change a mysql server variable on a pool of 100 mysql servers how would you do this? It's easy when it's one,two or even a dozen servers. just log in, change the my.cnf and change it "on the fly" if you can. Restart mysql if you can't.
You going to do that to 100 servers? It will take all day and be prone to failures. Scripting is the key here. Even just bash shell scripting can be very powerful. In another post I will cover a simple bash script to loop through a series of servers executing MySQL commands on them. Output can be logged for later analysis. Changes to the my.cnf in an automated method are a little more complex but can be accomplished with multiple methods. Perl and even php are quite common as scripting options as well. While I've done no study on this, it has been my experience that those are the top three scripting languages in that order.
It requires a bit of system administration skill for a large environment. Since I came from a sys admin background it wasn't a difficult transition at all. Even if you have no experience with scripting the basics can be learned within weeks or months. This can make a huge difference in your "employability" and this type of automation can make for a much more stable environment no matter the number of servers you manage.