The pt-online-schema-change tool has been a workhorse for years, allowing MySQL DBAs to alter tables with minimal impact to application workload, and before MySQL had native online alter capabilities. Although consistently grateful for the tool’s existence, I never liked the messiness of having to use and clean up triggers, and most DBAs have a horror story or two to tell about using any of the online alter methods.
When Github’s online schema transmogrifer (gh-ost; https://github.com/github/gh-ost) was released, then, I jumped on the chance to test it out.
Following are my testing notes. I tried out the flags available to run gh-ost from different locations in a replication setup, both functionally and under load. The load applied was via mysqlslap, using a …[Read more]