For starters, the requirement of a third-party library introduces at least two problems:

1. An additional potential point of failure 2. The core software (a DB, in this case) can (and probably will) evolve independently of the third-party tool--thus introducing an additional layer of maintenance problems.

I'd argue further--and this is of course just an opinion--that such a basic feature as this ought to be supported out-of-the-box by anything that claims to call itself a "database" in the sense that MySQL does.

Percona and pt-online-schema-change is not just "some third-party library".

It's an industry-standard tool and one of the most respected forks of MySQL. It's not a layer of maintenance problems and they sell commercial support.

Their customers include the BBC, Yelp, and Cisco: http://www.percona.com/about-us/customers

Also, for the record, Oracle added online schema changes in 5.6.

So you actually have to use a fork of MySQL to get online schema changes? I was thinking this was just a drop-in of some sort.

There is no "point". I asked a question and you didn't answer it directly.