We recently spent a few weeks trying to make it work in production, and couldn't. We always ran into deadlocks due to gap locking and auto_increment columns.

We recently spent a few weeks trying to make it work in production, and couldn't. We always ran into deadlocks due to gap locking and auto_increment columns. After a few weeks of failure, we finally gave up and did it the slow way, unweigh a slave, do the alter offline, catch up in replication, and fail over. Repeat as needed. Percona's OSC is great for the cases where it works, but there are still many cases where it doesn't.