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For those using MySQL: https://www.percona.com/doc/percona-toolkit/2.2/pt-online-sc...

"The technique of atomically renaming the original and new tables does not work when foreign keys refer to the table."

I think generally mysql shops that use pt-online-schema-change don't create foreign key constraints in production, sidestepping the whole problem this article is about.

Which is most of them that have enough traffic/data to need this tool in the first place. MySQL generally tends to perform badly at massive scale with foreign keys. (i.e., when your doing 30k queries/second)

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