It doesn't make the article less interesting but this statement is wrong most of the time
> This scenario is essentially identical to one in which there's a single migration statement that requires an `AccessExclusiveLock` and performs a table rewrite, such as adding a NOT NULL column with a DEFAULT value.
Unless the `DEFAULT` value is `VOLATILE` (this is rarely the case as usually default values are at least `STABLE`) no table rewrite is necessary since Postgres 11.
> Many other useful performance improvements, including the ability to avoid a table rewrite for ALTER TABLE ... ADD COLUMN with a non-null column default
Thanks, I will fix this part. As far as I can tell, it is only the example of what can cause the table rewrite that's wrong, so it would be correct if the example was to make a varchar shorter? Although I guess that's not a table rewrite, only a long validation...
> This scenario is essentially identical to one in which there's a single migration statement that requires an `AccessExclusiveLock` and performs a table rewrite, such as adding a NOT NULL column with a DEFAULT value.
Unless the `DEFAULT` value is `VOLATILE` (this is rarely the case as usually default values are at least `STABLE`) no table rewrite is necessary since Postgres 11.
https://www.postgresql.org/docs/devel/sql-altertable.html
> Many other useful performance improvements, including the ability to avoid a table rewrite for ALTER TABLE ... ADD COLUMN with a non-null column default
https://www.postgresql.org/docs/release/11.0/