Oracle 11g Invisible Indexes

SQL> create unique index EMP_UK1 on emp(empno) tablespace users invisible;

Index created.

SQL> select index_name, visibility from user_indexes where table_name='EMP';
INDEX_NAME VISIBILIT
------------------------------ ---------
EMP_UK1 INVISIBLE

SQL> explain plan for
2 select /*+ index(EMP_UK1) */ * from emp where empno=3999;

Explained.

SQL> select * from table(dbms_xplan.display);
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 3956160932
--------------------------------------------------------------------------
Id     Operation     Name     Rows     Bytes     Cost (%CPU)     Time
--------------------------------------------------------------------------
0  SELECT STATEMENT 1 53 83 (0) 00:00:04
* 1 TABLE ACCESS FULL EMP  1  53  83 (0) 00:00:04
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
1 - filter("EMPNO"=3999)
13 rows selected.

SQL> alter session set optimizer_use_invisible_indexes=true;
Session altered.

SQL> explain plan for
2 select /*+ index(EMP_UK1) */ * from emp where empno=3999;
Explained.

SQL> select * from table(dbms_xplan.display);
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 2080524269
---------------------------------------------------------------------------------------
Id     Operation     Name     Rows     Bytes     Cost (%CPU)     Time
---------------------------------------------------------------------------------------

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
0  SELECT STATEMENT  1  53  2 (0) 00: 00:01
1  TABLE ACCESS BY INDEX ROWID  EMP  1  53  2 (0)  00:00:01
* 2  INDEX UNIQUE SCAN  EMP_UK1  1  1 (0)  00:00:01
---------------------------------------------------------------------------------------

PLAN_TABLE_OUTPUT
-------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("EMPNO"=3999)

14 rows selected.