Oracle SQL Plan operation COLLECTION ITERATOR PICKLER FETCH

create type tq84_rec
   authid definer
as object
(
   col_one   number,
   col_two   varchar2(20)
);
/

create type tq84_tab as table of tq84_rec;
/

create function tq84_f return tq84_tab
   authid definer
as begin

    return tq84_tab(
       tq84_rec(42, 'forty-two'  ),
       tq84_rec( 1, 'one'        ),
       tq84_rec(99, 'ninety-nine')
    );

end tq84_f;
/

explain plan for
   select * from table(tq84_f);

select * from table(dbms_xplan.display(format=>'basic +rows,bytes'));
--
-- --------------------------------------------------------------------
-- | Id  | Operation                         | Name   | Rows  | Bytes |
-- --------------------------------------------------------------------
-- |   0 | SELECT STATEMENT                  |        |  8168 | 16336 |
-- |   1 |  COLLECTION ITERATOR PICKLER FETCH| TQ84_F |  8168 | 16336 |
-- --------------------------------------------------------------------

--
--  ==> As can be seen, by default, the COLLECTION ITERATOR
--      PICKLER FETCH operator expects 8168 rows / 16336 bytes.
--
--      The number of expected rows can be tweaked with the
--      OPT_ESTIMATE hint (which supersedes the CARDINALITY hint):
--
explain plan for
   select /*+ opt_estimate(table t rows=3) */
      *
   from
      table(tq84_f) t;

select * from table(dbms_xplan.display(format=>'basic +rows,bytes'));
--
-- --------------------------------------------------------------------
-- | Id  | Operation                         | Name   | Rows  | Bytes |
-- --------------------------------------------------------------------
-- |   0 | SELECT STATEMENT                  |        |     3 |     6 |
-- |   1 |  COLLECTION ITERATOR PICKLER FETCH| TQ84_F |     3 |     6 |
-- --------------------------------------------------------------------


drop function tq84_f;
drop type     tq84_tab;
drop type     tq84_rec;