читаем данные с дисков очень быстро...

SQL> SELECT /*+ PARALLEL(t) */ COUNT(*) FROM t;

   COUNT(*)
-----------
 1937420560

Elapsed: 00:00:24.17

---------------------------------------
| Id  | Operation                     
---------------------------------------
|   0 | SELECT STATEMENT              
|   1 |  SORT AGGREGATE               
|   2 |   PX COORDINATOR              
|   3 |    PX SEND QC (RANDOM)        
|   4 |     SORT AGGREGATE            
|   5 |      PX BLOCK ITERATOR        
|   6 |       TABLE ACCESS STORAGE FULL
---------------------------------------


Statistics
----------------------------------------------------------
      48  recursive calls
       0  db block gets
23233525  consistent gets
23105978  physical reads
       0  redo size
     526  bytes sent via SQL*Net to client
     524  bytes received via SQL*Net from client
       2  SQL*Net roundtrips to/from client
      16  sorts (memory)
       0  sorts (disk)
       1  rows processed

DP = 16 для 16 секций таблицы