BITMAP CONVERSION FROM ROWIDS

示例如下(请自己动手实验)：

create table test1 as select * from dba_objects;
create table test2 as select * from dba_objects;
create index idx1 on test1(object_id);
create index idx2 on test1(owner);
create index idx3 on test2(object_id);
create index idx4 on test2(owner);

BEGIN
  DBMS_STATS.GATHER_TABLE_STATS(ownname          => 'SCOTT',
                                tabname          => 'TEST1',
                                estimate_percent => 100,
                                method_opt       => 'for  columns owner size 200',
                                no_invalidate    => FALSE,
                                degree           => 1,
                                cascade          => TRUE);
END;
/

BEGIN
  DBMS_STATS.GATHER_TABLE_STATS(ownname          => 'SCOTT',
                                tabname          => 'TEST2',
                                estimate_percent => 100,
                                method_opt       => 'for  columns owner size 200',
                                no_invalidate    => FALSE,
                                degree           => 1,
                                cascade          => TRUE);
END;
/

比如这个SQL：

select * from test1 where owner='SCOTT' or object_id in(select object_id from test2 where owner='SCOTT');

执行计划如下：

select * from test1 where owner='SCOTT' or object_id in(select object_id from test2 where owner='SCOTT');

1859 rows selected.


Execution Plan
----------------------------------------------------------
Plan hash value: 4136318878

------------------------------------------------------------------------------------------
| Id  | Operation			 | Name  | Rows  | Bytes | Cost (%CPU)| Time	 |
------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT		 |	 |  5493 |   520K|   296   (1)| 00:00:04 |
|*  1 |  FILTER 			 |	 |	 |	 |	      | 	 |
|   2 |   TABLE ACCESS FULL		 | TEST1 | 74533 |  7060K|   296   (1)| 00:00:04 |
|   3 |   BITMAP CONVERSION TO ROWIDS	 |	 |     1 |    19 |     2   (0)| 00:00:01 |
|   4 |    BITMAP AND			 |	 |	 |	 |	      | 	 |
|   5 |     BITMAP CONVERSION FROM ROWIDS|	 |	 |	 |	      | 	 |
|*  6 |      INDEX RANGE SCAN		 | IDX3  |  1860 |	 |     1   (0)| 00:00:01 |
|   7 |     BITMAP CONVERSION FROM ROWIDS|	 |	 |	 |	      | 	 |
|*  8 |      INDEX RANGE SCAN		 | IDX4  |  1860 |	 |     1   (0)| 00:00:01 |
------------------------------------------------------------------------------------------

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

   1 - filter("OWNER"='SCOTT' OR  EXISTS (SELECT 0 FROM "TEST2" "TEST2" WHERE
	      "OBJECT_ID"=:B1 AND "OWNER"='SCOTT'))
   6 - access("OBJECT_ID"=:B1)
   8 - access("OWNER"='SCOTT')


Statistics
----------------------------------------------------------
	  1  recursive calls
	  0  db block gets
     475201  consistent gets
	  0  physical reads
	  0  redo size
      70860  bytes sent via SQL*Net to client
       1772  bytes received via SQL*Net from client
	125  SQL*Net roundtrips to/from client
	  0  sorts (memory)
	  0  sorts (disk)
       1859  rows processed


由于在test2上创建的都是单列索引:
create index idx3 on test2(object_id);
create index idx4 on test2(owner);


在test2上创建组合索引
create index idx5 on test2(object_id,owner);

SQL> select * from test1 where owner='SCOTT' or object_id in(select object_id from test2 where owner='SCOTT');

1859 rows selected.


Execution Plan
----------------------------------------------------------
Plan hash value: 4133849820

--------------------------------------------------------------------------------------
| Id  | Operation		     | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT	     |	     |	5493 |	 520K|	 296   (1)| 00:00:04 |
|*  1 |  FILTER 		     |	     |	     |	     |		  |	     |
|   2 |   TABLE ACCESS FULL	     | TEST1 | 74533 |	7060K|	 296   (1)| 00:00:04 |
|*  3 |   TABLE ACCESS BY INDEX ROWID| TEST2 |	   1 |	  19 |	   4   (0)| 00:00:01 |
|*  4 |    INDEX RANGE SCAN	     | IDX4  |	1860 |	     |	   1   (0)| 00:00:01 |
--------------------------------------------------------------------------------------

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

   1 - filter("OWNER"='SCOTT' OR  EXISTS (SELECT 0 FROM "TEST2" "TEST2" WHERE
	      "OWNER"='SCOTT' AND "OBJECT_ID"=:B1))
   3 - filter("OBJECT_ID"=:B1)
   4 - access("OWNER"='SCOTT')


Statistics
----------------------------------------------------------
	  1  recursive calls
	  0  db block gets
    2399432  consistent gets
	  0  physical reads
	  0  redo size
      70860  bytes sent via SQL*Net to client
       1772  bytes received via SQL*Net from client
	125  SQL*Net roundtrips to/from client
	  0  sorts (memory)
	  0  sorts (disk)
       1859  rows processed