selecting rowid slows down query

Hello

Oracle 9i, Windows and Solaris.

If I do a repeated full table scan and query that table's rowid, each query is slower than the preceding:

create table slow_rowid as
  select
    a.object_name || b.object_name foo, rownum bar   from
    all_objects a cross join all_objects b   where
    rownum <= 100000;

create procedure p_slow_rowid as
begin
  for r in (select rowid, foo, bar from slow_rowid) loop     null;
  end loop;
end;
/

set timing on

exec p_slow_rowid
exec p_slow_rowid
exec p_slow_rowid
exec p_slow_rowid
exec p_slow_rowid
exec p_slow_rowid
exec p_slow_rowid
exec p_slow_rowid
exec p_slow_rowid
exec p_slow_rowid
exec p_slow_rowid

I don't have an idea for this observation. Can someone explain why that happens and if it is possible to circumvent this behaviour?

Thanks
Rene

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