index range scan 单块读 无法走并行

SQL> create table t1 as select * from dba_objects;

SQL> create index i1_idx on t1(owner);

BEGIN
  DBMS_STATS.GATHER_TABLE_STATS(ownname          => 'TEST',
                                tabname          => 't1',
                                estimate_percent => 30,
                                method_opt       => 'for all columns size repeat',
                                no_invalidate    => FALSE,
                                degree           => 8,
                                cascade          => TRUE);
END;

SQL> select * from t1 where owner='TEST';

已选择3328行。


执行计划
----------------------------------------------------------
Plan hash value: 1104552013

--------------------------------------------------------------------------------------
| Id  | Operation		    | Name   | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT	    |	     |	 149K|	  13M|	4536   (1)| 00:00:55 |
|   1 |  TABLE ACCESS BY INDEX ROWID| T1     |	 149K|	  13M|	4536   (1)| 00:00:55 |
|*  2 |   INDEX RANGE SCAN	    | I1_IDX |	 152K|	     |	 361   (1)| 00:00:05 |
--------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   2 - access("OWNER"='TEST')


统计信息
----------------------------------------------------------
	  1  recursive calls
	  0  db block gets
	946  consistent gets
	258  physical reads
      18188  redo size
     309758  bytes sent via SQL*Net to client
       2846  bytes received via SQL*Net from client
	223  SQL*Net roundtrips to/from client
	  0  sorts (memory)
	  0  sorts (disk)



SQL>  select  /*+ parallel(a 4)*/ * from t1 a  where owner='TEST';

已选择3328行。


执行计划
----------------------------------------------------------
Plan hash value: 2494645258

--------------------------------------------------------------------------------------------------------------
| Id  | Operation	     | Name	| Rows	| Bytes | Cost (%CPU)| Time	|    TQ  |IN-OUT| PQ Distrib |
--------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT     |		|   149K|    13M|  4012   (1)| 00:00:49 |	 |	|	     |
|   1 |  PX COORDINATOR      |		|	|	|	     |		|	 |	|	     |
|   2 |   PX SEND QC (RANDOM)| :TQ10000 |   149K|    13M|  4012   (1)| 00:00:49 |  Q1,00 | P->S | QC (RAND)  |
|   3 |    PX BLOCK ITERATOR |		|   149K|    13M|  4012   (1)| 00:00:49 |  Q1,00 | PCWC |	     |
|*  4 |     TABLE ACCESS FULL| T1	|   149K|    13M|  4012   (1)| 00:00:49 |  Q1,00 | PCWP |	     |
--------------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   4 - filter("OWNER"='TEST')


统计信息
----------------------------------------------------------
	 13  recursive calls
	  0  db block gets
     131144  consistent gets
      65875  physical reads
	  0  redo size
     218981  bytes sent via SQL*Net to client
       2846  bytes received via SQL*Net from client
	223  SQL*Net roundtrips to/from client
	  0  sorts (memory)
	  0  sorts (disk)
       3328  rows processed


INDEX RANGE SCAN 单块读,无法走并行