gh-ost now powers our production schema migrations. We hit some serious limitations using pt-online-schema-change on our large volume, high traffic tables, to the effect of driving our database to a near grinding halt or even to the extent of causing outages. With gh-ost, we are now able to migrate our busiest tables at any time, peak hours and heavy workloads included, without causing impact to our service.
gh-ost supports testing in production. It goes a long way to build trust, both in integrity and in control. Are your databases just too busy and you cannot run existing online-schema-change tools? Have you suffered outages due to migrations? Are you tired of babysitting migrations that run up to 3:00am? Tired of being the only one tailing logs? Please, take a look at gh-ost. I believe it changes online migration paradigm.
gh-ost is open sourced under the MIT license.