Few months ago, I wrote about a faster way to do certain table modifications online. It works well when all you want is to remove auto_increment or change ENUM values. When it comes to changes that really require table to be rebuilt - adding/dropping columns or indexes, changing data type, converting data to different character set - MySQL master-master replication especially accompanied by MMM can be very handy to do the changes with virtually no downtime.
Couple of days ago I worked with one of our MySQL support customers as they were upgrading their application and mysql schema. We deployed and used MySQL Master-Master replication manager (MMM) ever since we started working so doing all the schema changes synchronously and with only couple seconds of “downtime” was really trivial. I’d like to share my experience.