全局索引与本地分区索引的一个重要区别

       全局索引和本地分区索引的概念很简单，全局索引，把索引建在一个段中，本地分区索引，按照每个分区来建索引，分区有多少个，分区索引就有多少个。DDL会使全局索引失效，而本地分区索引不受影响，这个对数据的维护意义重大。下面来做一个实验：

SQL> create table TEST

  2  (

  3    OWNER          VARCHAR2(30) not null,

  4    OBJECT_NAME    VARCHAR2(30) not null,

  5    SUBOBJECT_NAME VARCHAR2(30),

  6    OBJECT_ID      NUMBER not null,

  7    DATA_OBJECT_ID NUMBER,

  8    OBJECT_TYPE    VARCHAR2(19),

  9    CREATED        DATE not null,

 10    LAST_DDL_TIME  DATE not null,

 11    TIMESTAMP      VARCHAR2(19),

 12    STATUS         VARCHAR2(7),

 13    TEMPORARY      VARCHAR2(1),

 14    GENERATED      VARCHAR2(1),

 15    SECONDARY      VARCHAR2(1)

 16  )

 17  partition by list (OWNER)

 18  (

 19    partition PART_OWNER1 values ('SYS'),

 20    partition PART_OWNER2 values ('PUBLIC'),

 21    partition PART_OWNER3 values ('GG'),

 22    partition PART_OWNER4 values ('GG_ARCHIVE'),

 23    partition PART_OWNER5 values ('GG_QUERY'),

 24    partition PART_OWNER6 values ('DFWMS'),

 25    partition PART_OWNER7 values ('ORDSYS'),

 26    partition PART_OWNER8 values ('SYSMAN'),

 27    partition PART_OWNER9 values ('MDSYS'),

 28    partition PART_OWNER10 values ('OLAPSYS'),

 29    partition PART_OTHER values (default)

 30  );

表已创建。

SQL> insert into test select * from dba_objects where object_id is not null;

已创建89039行。

SQL> commit;

提交完成。

SQL> create index ind_g_object_id on test(object_id);  
----建立全局索引
索引已创建。

SQL> exec dbms_stats.gather_table_stats(user,'test',cascade => true);

PL/SQL 过程已成功完成。

SQL> set autotrace trace exp

SQL> select * from test where object_id = 17689;

执行计划

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

Plan hash value: 2926561466

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

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

p |

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

|   0 | SELECT STATEMENT                   |                 |   1 |    93 |     2   (0)| 00:00:01|       ||

|   1 |  TABLE ACCESS BY GLOBAL INDEX ROWID| TEST            |   1 |    93 |     2   (0)| 00:00:01| ROWID | ROWID |
|*  2 |   INDEX RANGE SCAN                 | IND_G_OBJECT_ID |   1 |       |     1   (0)| 00:00:01|       ||  
---索引扫描
-------------------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):

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

   2 - access("OBJECT_ID"=17689)

SQL> set autotrace off
SQL> alter table test drop partition PART_OWNER9;     
---删除一个分区
表已更改。

SQL> set autotrace trace exp

SQL> select * from test where object_id = 76154;

执行计划

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

Plan hash value: 4170016888

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

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

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

|   0 | SELECT STATEMENT   |      |     1 |    93 |   318   (1)| 00:00:04 |       |       |

|   1 |  PARTITION LIST ALL|      |     1 |    93 |   318   (1)| 00:00:04 |     1 |    10 |
|*  2 |   TABLE ACCESS FULL| TEST |     1 |    93 |   318   (1)| 00:00:04 |     1 |    10 |    
---索引失效，变为了全表扫描
-------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):

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

   2 - filter("OBJECT_ID"=76154)

SQL> drop index ind_g_object_id;

索引已删除。

SQL> create index ind_l_object_id on test(object_id) local;
--- 建立本地分区索引
索引已创建。

SQL> select * from test where object_id = 76154;

执行计划

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

Plan hash value: 2133679295

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

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

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

---

|   0 | SELECT STATEMENT                   |                 |    1 |    93 |    12   (0)| 00:00:01 |       ||

|   1 |  PARTITION LIST ALL                |                 |    1 |    93 |    12   (0)| 00:00:01 |     1 |    10 |
|   2 |   TABLE ACCESS BY LOCAL INDEX ROWID| TEST            |    1 |    93 |    12   (0)| 00:00:01 |     1 |    10 | 
---
索引扫描
|*  3 |    INDEX RANGE SCAN                | IND_L_OBJECT_ID |    1 |       |    11   (0)| 00:00:01 |     1 |    10 |

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

Predicate Information (identified by operation id):

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

   3 - access("OBJECT_ID"=76154)

SQL> alter table test drop partition PART_OWNER5;
----删除一个分区


表已更改。

SQL> select * from test where object_id = 76154;

执行计划

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

Plan hash value: 2133679295

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

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

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

|   0 | SELECT STATEMENT                   |                 |     1 |    93 |    11   (0)| 00:00:01 |       ||

|   1 |  PARTITION LIST ALL                |                 |     1 |    93 |    11   (0)| 00:00:01 |     1 |9 |
|   2 |   TABLE ACCESS BY LOCAL INDEX ROWID| TEST            |     1 |    93 |    11   (0)| 00:00:01 |     1 |9 |  
--- 依然索引扫描
|*  3 |    INDEX RANGE SCAN                | IND_L_OBJECT_ID |     1 |       |    10   (0)| 00:00:01 |     1 |9 |

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

Predicate Information (identified by operation id):

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

   3 - access("OBJECT_ID"=76154)