I wanted to track the delay of a mysql slave server in Munin, and found nothing appropriate after a quick google. So, in case anyone else finds it useful, here is a plugin which will allow you to do just that.
Here’s a typical graph:
Download: mysql_slave (1 Kb)
EDIT: I wrote this so I could better understand the recovery time of a slave which had 13 hours of updates to catch up on. While it was good for that, it’s less useful for the day-to-day lag as munin will only be polling it every 5 minutes. A better way would be to use mk-heartbeat to get a more accurate moving average.