位图索引的一个小测试

总结：
在OLTP系统下，如果查询条件是多列，多变的时候使用位图索引，但是在OLAP系统下，不能建立位图索引，

比如说我要修改的是owner='SYS'，那么owner='SYS'这一列就会被锁。

测试：

a,b,c,d,e
1、a,b,c
2、a,b,d
3、b,c,d

select count(*)
  from t1
 where owner = 'SYS'
   and object_type = 'TABLE'
   and status = 'VALID';

--建组合索引。
--在三个列上单独建立索引

create   index idx_1 on t1(owner);
create   index idx_2 on t1(object_type);
create   index idx_3 on t1(status);
执行计划
----------------------------------------------------------
Plan hash value: 2712755765


--------------------------------------------------------------------------------------
| Id  | Operation                    | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT             |       |     1 |    33 |   174   (0)| 00:00:03 |
|   1 |  SORT AGGREGATE              |       |     1 |    33 |            |          |
|*  2 |   TABLE ACCESS BY INDEX ROWID| T1    |  2343 | 77319 |   174   (0)| 00:00:03 |
|*  3 |    INDEX RANGE SCAN          | IDX_2 |  4157 |       |    11   (0)| 00:00:01 |
--------------------------------------------------------------------------------------


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


   2 - filter("OWNER"='SYS' AND "STATUS"='VALID')
   3 - access("OBJECT_TYPE"='TABLE')


Note
-----
   - dynamic sampling used for this statement (level=2)




统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
        275  consistent gets
          0  physical reads
          0  redo size
        528  bytes sent via SQL*Net to client
        520  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed
drop index idx_1;
drop index idx_2;
drop index idx_3;

--建立位图索引，位图索引是进行AND运算，然后根据位图转换成count

create bitmap index idx_1 on t1(owner);
create bitmap index idx_2 on t1(object_type);
create bitmap index idx_3 on t1(status);
SQL> select count(*)
  2    from t1
  3   where owner = 'SYS'
  4     and object_type = 'TABLE'
  5     and status = 'VALID';

执行计划
----------------------------------------------------------
Plan hash value: 467448745


--------------------------------------------------------------------------------------
| Id  | Operation                    | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT             |       |     1 |    33 |     3   (0)| 00:00:01 |
|   1 |  SORT AGGREGATE              |       |     1 |    33 |            |          |
|   2 |   BITMAP CONVERSION COUNT    |       |  2343 | 77319 |     3   (0)| 00:00:01 |
|   3 |    BITMAP AND                |       |       |       |            |          |
|*  4 |     BITMAP INDEX SINGLE VALUE| IDX_2 |       |       |            |          |
|*  5 |     BITMAP INDEX SINGLE VALUE| IDX_1 |       |       |            |          |
|*  6 |     BITMAP INDEX SINGLE VALUE| IDX_3 |       |       |            |          |
--------------------------------------------------------------------------------------


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


   4 - access("OBJECT_TYPE"='TABLE')
   5 - access("OWNER"='SYS')
   6 - access("STATUS"='VALID')

Note
-----
   - dynamic sampling used for this statement (level=2)

统计信息
----------------------------------------------------------
         63  recursive calls
          0  db block gets
         94  consistent gets
         24  physical reads
          0  redo size
        528  bytes sent via SQL*Net to client
        520  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

--假如最后结果：1 0 0 1 1  1 0 1，因为求得是count,只需要数1就可以。
--如果是求*，那么位图转换成ROWID，根据ROWID回表。

执行计划
----------------------------------------------------------
Plan hash value: 1851967648


--------------------------------------------------------------------------------------
| Id  | Operation                    | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT             |       |  2343 |   473K|     3   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID | T1    |  2343 |   473K|     3   (0)| 00:00:01 |
|   2 |   BITMAP CONVERSION TO ROWIDS|       |       |       |            |          |
|   3 |    BITMAP AND                |       |       |       |            |          |
|*  4 |     BITMAP INDEX SINGLE VALUE| IDX_2 |       |       |            |          |
|*  5 |     BITMAP INDEX SINGLE VALUE| IDX_1 |       |       |            |          |
|*  6 |     BITMAP INDEX SINGLE VALUE| IDX_3 |       |       |            |          |
--------------------------------------------------------------------------------------


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


   4 - access("OBJECT_TYPE"='TABLE')
   5 - access("OWNER"='SYS')
   6 - access("STATUS"='VALID')


Note
-----
   - dynamic sampling used for this statement (level=2)




统计信息
----------------------------------------------------------
        424  recursive calls
          0  db block gets
        384  consistent gets
          3  physical reads
          0  redo size
     202270  bytes sent via SQL*Net to client
       1917  bytes received via SQL*Net from client
        129  SQL*Net roundtrips to/from client
          6  sorts (memory)
          0  sorts (disk)
       1915  rows processed