Package to determine amount of redo generated in Oracle

reate table last_redo_size as select value redo_size 
 from v$sysstat where name = 'redo size';


create or replace package redo_diff as
  procedure diff_it;
end;
/

create or replace package body redo_diff as
  s number;

  function get_size return number is
    s_ number;
  begin
    select value into s_ from sys.v_$sysstat where name = 'redo size';
    return s_;
  end get_size;
 
  procedure diff_it is
    s_new number;
  begin
    s_new := get_size; 
    dbms_output.put_line('redo diff: ' || to_char(s_new - s));
    s    := s_new;
  end diff_it;

  begin
    s := get_size;
end;
/