[fipar]

With gh-ost migrations are performed on a copy of the table. This, combined with the way data is copied to this table mean: - you can pause just by suspending the copy, - changes are invisible until the end, when tables are swapped.

The first point depends on the mechanism used to keep up with changes to the original table. You can’t fully pause migrations on pt-online-schema-change for example, as it leverages triggers for that part.

From my phone so sorry if too brief, gh-ost’s docs are great and would tell the whole story.