Extremely long postgres query
Postgres 11 added a feature where a table rewrite is not necessary if you add a column with a default value. 

If you had used

alter table big_and_loaded_table
    add column col1 boolean default false;


the statement would have executed nearly instantaneous with the same effect. 

But an ALTER TABLE statement will acquire an exclusive lock to prevent access to the table while it's being changed, there is no way around it.