Starting or stopping MySQL in Linux (CentOS)
service mysqld start
service mysqld stop
service mysqld restart
Restarting MySQL should only take a second or so. I would be surprised if many of your users noticed that you did it. In saying that, don’t do it unless you have spare time to deal with a failure to restart. You might have made a mistake in the config file and that can stop MySQL starting again.
Your database might appear slower immediately following a restart. This is normal, because you have lost all your cached data/queries. You shouldn’t experience too much of a slow down, but it’s worth noting, just in case.