Recently I faced the problem that my Db became very huge and I cannot allow to myself downtime every time when I want to change the schema.
This caused me to start looking for solution that do schema changing online.
1) pt-online-schema-change. Very attractive project, but honestly I was disappointed. Having downloaded the newest version, I had to change the code in order to get the script working. At the beggining script fails with error messages. All of them I found on the bug report of Percona. After patching script did it's job, hopefully well.
2) oak-online-alter-table. Also very interesting project, facebook mentioned it as good product on Online Schema Change for MySQL. Tomorrow I gonna try it.
If you are more experienced, please share with us your opinion. What's the best and most reliable product?