SQL> SELECT COUNT(*) FROM linyu.hwm;

Execution Plan
----------------------------------------------------------
Plan hash value: 3274855064

-------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Cost (%CPU)| Time     |
-------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |     1 |   464   (2)| 00:00:06 |
|   1 |  SORT AGGREGATE    |      |     1 |            |          |
|   2 |   TABLE ACCESS FULL| HWM  |   149K|   464   (2)| 00:00:06 |
-------------------------------------------------------------------

Statistics
----------------------------------------------------------
          1  recursive calls
          0  db block gets
       2076  consistent gets
          0  physical reads
          0  redo size
        413  bytes sent via SQL*Net to client
        385  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

SQL> alter session set db_file_multiblock_read_count=8;

Session altered.

SQL>  SELECT COUNT(*) FROM linyu.hwm;

Execution Plan
----------------------------------------------------------
Plan hash value: 3274855064

-------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Cost (%CPU)| Time     |
-------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |     1 |   573   (1)| 00:00:07 |
|   1 |  SORT AGGREGATE    |      |     1 |            |          |
|   2 |   TABLE ACCESS FULL| HWM  |   149K|   573   (1)| 00:00:07 |
-------------------------------------------------------------------

Statistics
----------------------------------------------------------
          1  recursive calls
          0  db block gets
       2076  consistent gets
          0  physical reads
          0  redo size
        413  bytes sent via SQL*Net to client
        385  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

SQL>