Oracle TABLE ACCESS BY INDEX ROWID 说明


一.  测试环境

SQL> select * from v$version where rownum=1; 

BANNER

--------------------------------------------------------------------------------

Oracle Database 11g Enterprise Edition Release11.2.0.3.0 - 64bit Production 

SQL> create table dave as selectobject_id,object_name,object_type,created,timestamp,status from all_objects;

表已创建。 

SQL> create table dave2 as select * from dave;

表已创建。 

--收集统计信息，这里没有收集直方图：

SQL> exec dbms_stats.gather_table_stats(ownname=>'SYS',tabname =>'DAVE',estimate_percent => 10 ,method_opt =>'FORCOLUMNS size 1',degree=>10,cascade => true); 

PL/SQL 过程已成功完成。 

SQL> exec dbms_stats.gather_table_stats(ownname=>'SYS',tabname =>'DAVE2',estimate_percent => 10 ,method_opt =>'FORCOLUMNS size 1',degree=>10,cascade => true); 

PL/SQL 过程已成功完成。 

--避免其他影响，先刷新buffer cache：

SQL> alter system flush buffer_cache; 

系统已更改。 

--查看全表扫描时的执行计划：

SQL> set autot traceonly 

SQL> select d1.object_name,d2.object_type fromdave d1,dave2 d2 where d1.object_id=d2.object_id; 

已选择72762行。 

执行计划

----------------------------------------------------------

Plan hash value: 3613449503 

------------------------------------------------------------------------------------

| Id  |Operation          | Name  | Rows | Bytes |TempSpc| Cost (%CPU)| Time    |

------------------------------------------------------------------------------------

|   0 |SELECT STATEMENT   |       | 72520 |  3824K|      |   695   (1)| 00:00:09 |

|*  1 |  HASH JOIN         |      | 72520 |  3824K|  2536K|  695   (1)| 00:00:09 |

|   2 |   TABLE ACCESS FULL| DAVE2 | 71990 |  1687K|      |   213   (1)| 00:00:03 |

|   3 |   TABLE ACCESS FULL| DAVE  | 72520 | 2124K|       |   213  (1)| 00:00:03 |

------------------------------------------------------------------------------------ 

Predicate Information (identified by operation id):

--------------------------------------------------- 

   1 -access("D1"."OBJECT_ID"="D2"."OBJECT_ID") 

统计信息

----------------------------------------------------------

         0  recursive calls

         0  db block gets

      6353  consistent gets

       1558  physical reads

         0  redo size

   3388939  bytes sent via SQL*Net toclient

     53874  bytes received via SQL*Netfrom client

      4852  SQL*Net roundtrips to/fromclient

         0  sorts (memory)

         0  sorts (disk)

     72762  rows processed

--这里产生了1558的物理读

SQL> 

--在object_id上创建索引： 

SQL> create index idx_dave_object_idon dave(object_id);

索引已创建。

SQL> create index idx_dave_object_id2 ondave2(object_id);

索引已创建。 

--在次查看执行计划： 

SQL> select d1.object_name,d2.object_type fromdave d1,dave2 d2 where d1.object_id=d2.object_id; 

已选择72762行。 

执行计划

----------------------------------------------------------

Plan hash value: 3613449503

 

------------------------------------------------------------------------------------

| Id  |Operation          | Name  | Rows | Bytes |TempSpc| Cost (%CPU)| Time    |

------------------------------------------------------------------------------------

|   0 |SELECT STATEMENT   |       | 72520 |  3824K|      |   695   (1)| 00:00:09 |

|*  1 |  HASH JOIN         |      | 72520 |  3824K|  2536K|  695   (1)| 00:00:09 |

|   2 |   TABLE ACCESS FULL| DAVE2 | 71990 |  1687K|      |   213   (1)| 00:00:03 |

|   3 |   TABLE ACCESS FULL| DAVE  | 72520 | 2124K|       |   213  (1)| 00:00:03 |

------------------------------------------------------------------------------------ 

Predicate Information (identified by operation id):

--------------------------------------------------- 

   1 -access("D1"."OBJECT_ID"="D2"."OBJECT_ID") 

统计信息

----------------------------------------------------------

         1  recursive calls

         0  db block gets

      6353  consistent gets

          0  physical reads

         0  redo size

   3388939  bytes sent via SQL*Net toclient

     53874  bytes received via SQL*Netfrom client

      4852  SQL*Net roundtrips to/fromclient

         0  sorts (memory)

         0  sorts (disk)

     72762  rows processed 

这里的物理读为0. 但是还是走的是全表扫描。 

--刷新一下buffer，增加索引条件：

SQL> alter system flush buffer_cache; 

系统已更改。 

SQL> select d1.object_name,d2.object_type fromdave d1,dave2 d2 where d1.object_id=d2.object_id  and d1.object_id <100; 

已选择98行。 

执行计划

----------------------------------------------------------

Plan hash value: 504164237 

----------------------------------------------------------------------------------------------------

| Id  |Operation                    | Name                | Rows  | Bytes | Cost (%CPU)| Time     |

----------------------------------------------------------------------------------------------------

|   0 |SELECT STATEMENT             |                     |  3600 |  189K|    23   (5)| 00:00:01 |

|*  1 |  HASH JOIN                   |                     |  3600 |  189K|    23   (5)| 00:00:01 |

|   2 |   TABLE ACCESS BY INDEX ROWID| DAVE2               |  3600 | 86400 |    11  (0)| 00:00:01 |

|*  3 |    INDEX RANGE SCAN          | IDX_DAVE_OBJECT_ID2 |   648 |      |     3   (0)| 00:00:01 |

|   4 |   TABLE ACCESS BY INDEX ROWID| DAVE                |  3626 |  106K|    11   (0)| 00:00:01 |

|*  5 |    INDEX RANGE SCAN          | IDX_DAVE_OBJECT_ID  |   653|       |     3  (0)| 00:00:01 |

---------------------------------------------------------------------------------------------------- 

Predicate Information (identified by operation id):

---------------------------------------------------

 

   1 -access("D1"."OBJECT_ID"="D2"."OBJECT_ID")

   3 -access("D2"."OBJECT_ID"<100)

   5 -access("D1"."OBJECT_ID"<100) 

统计信息

----------------------------------------------------------

         1  recursive calls

         0  db block gets

        20  consistent gets

         6  physical reads

         0  redo size

      3317  bytes sent via SQL*Net toclient

       590  bytes received via SQL*Netfrom client

         8  SQL*Net roundtrips to/fromclient

         0  sorts (memory)

         0  sorts (disk)

        98  rows processed

SQL> 

走索引之后，物理读从1558降到6.  

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