[jeltz]

> ... only if you're truncating the whole db and re-initializing the schema, no?

Nope. In PostgreSQL the cost of truncating tables is proportional to the number of tables while doing a rollback is constant time (and a low constant at that, less than a commit for example).

In other databases like MySQL I believe truncating data is still proportional to the number of tables while rollback is proportional to the amount of data inserted or updated. So which is cheaper depends on your application.