隐含参数_db_block_numa

SQL> select
2    x.ksppinm  name,
3    y.ksppstvl  value,
4    y.ksppstdf  isdefault,
5    decode(bitand(y.ksppstvf,7),1,'MODIFIED',4,'SYSTEM_MOD','FALSE')  ismod,
6    decode(bitand(y.ksppstvf,2),2,'TRUE','FALSE')  isadj
7  from
8    sys.x$ksppi x,
9    sys.x$ksppcv y
10  where
11    x.inst_id = userenv('Instance') and
12    y.inst_id = userenv('Instance') and
13    x.indx = y.indx and
14    x.ksppinm like '%_optimizer_skip_scan_enabled%'
15  order by
16    translate(x.ksppinm, ' _', ' ');

NAME                      VALUE                     ISDEFAULT ISMOD      ISADJ
------------------------- ------------------------- --------- ---------- -----
_optimizer_skip_scan_enab TRUE                      TRUE      FALSE      FALSE
led

SQL> create index ind_test on test(object_type,object_id,object_name);

Index created.

SQL> analyze table test compute statistics for all indexed columns;

Table analyzed.

SQL> select object_id from test where object_type='INDEX PARTITION' and rownum<2;

OBJECT_ID
----------
5851

SQL> alter session set "_optimizer_skip_scan_enabled"=false;

Session altered.

SQL> select * from test where object_id=5851;

Execution Plan
----------------------------------------------------------
Plan hash value: 1357081020

--------------------------------------------------------------------------
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |      |     1 |   312 |   415   (1)| 00:00:01 |
|*  1 |  TABLE ACCESS FULL| TEST |     1 |   312 |   415   (1)| 00:00:01 |
--------------------------------------------------------------------------

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

1 - filter("OBJECT_ID"=5851)

Note
-----
- dynamic statistics used: dynamic sampling (level=2)

Statistics
-----------------------------------------------
4000
-----------
20  recursive calls
0  db block gets
1622  consistent gets
1566  physical reads
0  redo size
1877  bytes sent via SQL*Net to client
543  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 "_optimizer_skip_scan_enabled"=true;

Session altered.

SQL> select * from test where object_id=5851;

Execution Plan
----------------------------------------------------------
Plan hash value: 4219850847

------------------------------------------------------------------------------------------------
| Id  | Operation                           | Name     | Rows  | Bytes | Cost (%CPU)| Time     |
------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                    |          |     1 |   312 |    47   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID BATCHED| TEST     |     1 |   312 |    47   (0)| 00:00:01 |
|*  2 |   INDEX SKIP SCAN                   | IND_TEST |     1 |       |    46   (0)| 00:00:01 |
------------------------------------------------------------------------------------------------

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

2 - access("OBJECT_ID"=5851)
filter("OBJECT_ID"=5851)

Note
-----
- dynamic statistics used: dynamic sampling (level=2)

Statistics
----------------------------------------------------------
5  recursive calls
0  db block gets
102  consistent gets
31  physical reads
0  redo size
1881  bytes sent via SQL*Net to client
543  bytes received via SQL*Net from client
2  SQL*Net roundtrips to/from client
0  sorts (memory)
0  sorts (disk)
1  rows processed