Oracle TABLE ACCESS BY INDEX ROWID 说明

数据库|mysql教程 Oracle TABLE ACCESS BY INDEX ROWID 说明

Oracle高级培训,Oracle TABLE ACCESS

数据库-mysql教程

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Oracle TABLE ACCESS BY INDEX ROWID 说明，rowid是伪列（pseudocolumn），在查询结果输出时它被构造出来的。rowid并不会真正存在

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一. 测试环境

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

BANNER

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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。

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

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————————————————————————————

| 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

SQL>

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

————————————————————————————

————————————————————————————

| 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。

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

—————————————————————————————————-

—————————————————————————————————-

| 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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Oracle高级培训