I'm adding a number of columns with DEFAULT values that are NULLABLE to a large table

e.g

alter table big_table add (col1 varchar2(1) default 0, col2 varchar2(1) default 0);

It's taking a long time to do because Oracle is executing a bit of recursive SQL like this behind the scenes when the ALTER TABLE is submitted;

update big_table set col1 = '0', col2 = '0'

From experience of enabling foreign key constraint in PARALLEL, I did this;

alter session force parallel dml;
alter session force parallel query;
alter session force parallel ddl;
alter table big_table parallel;

-- now do my foreign key constraints => first enable novalidate, then validate

alter table big_table noparallel;

The above works and forces the recursive SQL that Oracle executes when validating the FK constraint to be executed in PARALLEL.

However, applying the same approach I had used for enabling FK constraint in PARALLEL to adding NULLABLE columns with DEFAULT values - it's not working, the recursive UPDATE above is refusing to go PARALLEL (even though the execution PLAN is showing PARALLEL).

Am I missing a "trick" ? Or has this improved in a later version of Oracle, 12c onwards,etc ?

If I can get that recursive UPDATE to go PARALLEL, I know then the ALTER will be much quicker, because as a separate test, I ran that UPDATE standalone in PARALLEL, and it did go PARALLEL and completed very quickly.

All statistics are up to date.

alter table big_table add ( 
  col1 varchar2(1) default 0 not null, 
  col2 varchar2(1) default 0 not null
);

alter table t 
  modify ( col1 null, col2 null );