drop table if exists tab;
create unlogged table tab (a int4, b int4, f3 int, f4 int, f5 text,
  f6 float8, f7 int, f8 int, f9 int, f10 int);
\timing on
insert into tab select g, g, g, g, g::text,
  g, g, g, g, g
  from generate_series(1, 10000000) g;
vacuum tab;
explain verbose update tab set b = b, f6 = f6;
update tab set b = b, f6 = f6;