Oracle SQL Plan operation PX BLOCK ITERATOR

create table tq84_tab (
   num   integer           check (num between 1 and 100000) not null,
   txt  varchar2(10)
);
 
insert into tq84_tab
select
   level,
   dbms_random.string('a', 10)
from
   dual
connect by level <= 100000;
 
explain plan for
select /*+ parallel */
   max(txt)
from
   tq84_tab
;  
 
 
select * from dbms_xplan.display(format=>'basic');
--
-- -------------------------------------------
-- | Id  | Operation              | Name     |
-- -------------------------------------------
-- |   0 | SELECT STATEMENT       |          |
-- |   1 |  SORT AGGREGATE        |          |
-- |   2 |   PX COORDINATOR       |          |
-- |   3 |    PX SEND QC (RANDOM) | :TQ10000 |
-- |   4 |     SORT AGGREGATE     |          |
-- |   5 |      PX BLOCK ITERATOR |          |
-- |   6 |       TABLE ACCESS FULL| TQ84_TAB |
-- -------------------------------------------

drop table tq84_tab;