> Adding a column, changing column's nullability and adding/changing constraints is already zero-downtime in PG. Making a previously nullable column NOT NULL i

> Adding a column, changing column's nullability and adding/changing constraints is already zero-downtime in PG. Making a previously nullable column NOT NULL is not zero downtime. Neither are adding constraints -- except in some cases with NOT VALID, which isn't quite the same thing. > Dropping a column and changing the data type are not zero-downtime. Dropping a column is zero downtime.