[ReidZB]

They do, and obviously it is workable, but I think every big MySQL org ends up with a tool/workflow like gh-ost: https://github.com/github/gh-ost which have their own set of challenges, like not playing well with foreign keys.

[kbenson]

Or the Percona tools, which support stuff like online schema change.

[evanelias]

Big MySQL orgs are sharded, which greatly reduces the utility of foreign key constraints anyway.