drop table if exists document;
drop table if exists document_file ;

create table document (document_type_id int, id int primary key);
create table document_file (document_type_id int, document_id int primary key,
   filler char(600));

insert into document_file select x,x,'z' from generate_series(1,4000000) x;
insert into document select x,x from generate_series(1,4000000) x;

analyze document_file;
analyze document;

set enable_mergejoin = false;

explain analyze UPDATE ONLY document_file AS df SET document_type_id = d.document_type_id FROM document AS d WHERE d.id = document_id;