oracle 并行不生效,并行的hint不生效

SQL> set autotrace on

SQL> create table aaaa as select * from dba_tables;

Table created.

SQL> select /*+ parallel(a,2) */count(*) from aaaa a;

COUNT(*)

----------

943

Execution Plan

----------------------------------------------------------

Plan hash value: 2947485748

--------------------------------------------------------------------------------------------------------

| Id  | Operation              | Name     | Rows  | Cost (%CPU)| Time     |    TQ  |IN-OUT| PQ Distrib |

--------------------------------------------------------------------------------------------------------

|   0 | SELECT STATEMENT       |          |     1 |  &