With a sane migration tool like pt-osc or gh-ost you can absolutely abort in the middle. What's more, you can pause in the middle or even slow down in the middle based on arbitrary logic (ie, pause migration if replication delay rises above a certain value). Postgres is nice and transactional DDL has its place but postgres stopped halfway through IMO. Vanilla Postgres > vanilla MySQL, but the migration story of MySQL + tooling is so far beyond Postgres + tooling that it's not even funny.
That said, if you don't expect to have tables with 100m+ rows, even vanilla postgres will be good enough.
That said, if you don't expect to have tables with 100m+ rows, even vanilla postgres will be good enough.