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by postgressomethi 1833 days ago
> 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.