Oracle 分区索引初步理解
[日期：2011-11-26] 来源：Linux社区 作者：aqszhuaihuai
Oracle 分区索引
分区索引类型：局部分区索引与全局分区索引。局部分区索引使用与底层表相同的机制分区;全局分区索引使用与底层表不同的机制进行分区，索引按区间或散列对索引进行分区，一个全局索引分区可能指向任何表分区或所有表分区。
对于local索引，每一个表分区对应一个索引分区，当表的分区发生变化时，索引的维护由Oracle自动进行。
对于global索引，可以选择是否分区，而且索引的分区可以不与表分区相对应。当对分区进行维护操作时，通常会导致全局索引的INVALID，必须在执行完操作后 REBUILD。Oracle9i提供了UPDATE GLOBAL INDEXES语句，可以在进行分区维护的同时重建全局索引，UPDATE GLOBAL INDEXES是一种允许用资源耗费的增加来换取可用性的选项。
局部索引比全局索引容易管理,而全局索引比较快。
局部索引多应用于数据仓库环境中，而全局索引多应用于oltp系统中。
局部前缀索引与局部非前缀索引：
如果局部索引的索引列以分区键开头，则称为前缀局部索引。
如果局部索引的列不是以分区键开头，或者不包含分区键列，则称为非前缀索引。
像下面这样的查询（a为分区键）：
Select … from partitioned_table where a=a:aand b=:b;
Select … from partitioned_table where b=:b;
可以考虑在(b,a)上建立局部非前缀索引。而如果在(a,b)上建立局部前缀索引，第二个查询不会走索引。
create table range
(id int,
name varchar2(20) ,
address varchar2(10)
)
partition by range(address)
(
partition p1 values less than('A') ,
partition p2 values less than('F') ,
partition p3 values less than('Y') ,
partition p4 values less than('Z')
)
13 /
Table created.
SQL> insert into range select rownum,owner,'A' from dba_objects where rownum<1000;
999 rows created.
SQL> insert into range select rownum 999,owner,'F' from dba_objects where rownum<1000;
999 rows created.
SQL> select max(id) from range;
MAX(ID)
----------
1998
SQL> insert into range select rownum 999 999,owner,'Y' from dba_objects where rownum<1000;
999 rows created.
SQL> commit;
Commit complete.
SQL> select name,count(name) from range group by name;
NAME COUNT(NAME)
-------------------- -----------
PUBLIC 237
OUTLN 21
SYS 2739
SQL> set autot traceonly
SQL> select id,name,address from range where address='Y' and name='OUTLN';
7 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 955737907
------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | Pstart| Pstop |
------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 7 | 224 | 2 (0)| 00:00:01 | | |
| 1 | PARTITION RANGE SINGLE| | 7 | 224 | 2 (0)| 00:00:01 | 4 | 4 |
|* 2 | TABLE ACCESS FULL | RANGE | 7 | 224 | 2 (0)| 00:00:01 | 4 | 4 |
------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter("ADDRESS"='Y' AND "NAME"='OUTLN')
Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
6 consistent gets
0 physical reads
0 redo size
610 bytes sent via SQL*Net to client
385 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
7 rows processed
SQL> select id,name,address from range where name='OUTLN';
21 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 184025858
---------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | Pstart| Pstop |
---------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 21 | 672 | 4 (0)| 00:00:01 | | |
| 1 | PARTITION RANGE ALL| | 21 | 672 | 4 (0)| 00:00:01 | 1 | 4 |
|* 2 | TABLE ACCESS FULL | RANGE | 21 | 672 | 4 (0)| 00:00:01 | 1 | 4 |
---------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter("NAME"='OUTLN')
Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
5 recursive calls
0 db block gets
42 consistent gets
0 physical reads
0 redo size
867 bytes sent via SQL*Net to client
396 bytes received via SQL*Net from client
3 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
21 rows processed
SQL> create index idx_pre on range(address,name) local; --建立前缀索引
Index created.
SQL> select id,name,address from range where address='Y' and name='OUTLN';
7 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 1638943077
--------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | Pstart| Pstop |
--------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 7 | 224 | 2 (0)| 00:00:01 | | |
| 1 | PARTITION RANGE SINGLE | | 7 | 224 | 2 (0)| 00:00:01 | 4 | 4 |
| 2 | TABLE ACCESS BY LOCAL INDEX ROWID| RANGE | 7 | 224 | 2 (0)| 00:00:01 | 4 | 4 |
|* 3 | INDEX RANGE SCAN | IDX_PRE | 1 | | 1 (0)| 00:00:01 | 4 | 4 |
--------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - access("ADDRESS"='Y' AND "NAME"='OUTLN')
Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
5 consistent gets
0 physical reads
0 redo size
610 bytes sent via SQL*Net to client
385 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
7 rows processed
SQL> select /* index(range idx_pre)*/ id,name,address from range where name='OUTLN'; --没有使用索引
21 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 184025858
---------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | Pstart| Pstop |
---------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 21 | 672 | 4 (0)| 00:00:01 | | |
| 1 | PARTITION RANGE ALL| | 21 | 672 | 4 (0)| 00:00:01 | 1 | 4 |
|* 2 | TABLE ACCESS FULL | RANGE | 21 | 672 | 4 (0)| 00:00:01 | 1 | 4 |
---------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter("NAME"='OUTLN')
Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
5 recursive calls
0 db block gets
42 consistent gets
0 physical reads
0 redo size
867 bytes sent via SQL*Net to client
396 bytes received via SQL*Net from client
3 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
21 rows processed
SQL> create index idx_nonpre on range(name,address) local;
Index created.
SQL> select id,name,address from range where address='Y' and name='OUTLN';
7 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 1326523914
-----------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | Pstart| Pstop |
-----------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 7 | 224 | 2 (0)| 00:00:01 | | |
| 1 | PARTITION RANGE SINGLE | | 7 | 224 | 2 (0)| 00:00:01 | 4 | 4 |
| 2 | TABLE ACCESS BY LOCAL INDEX ROWID| RANGE | 7 | 224 | 2 (0)| 00:00:01 | 4 | 4 |
|* 3 | INDEX RANGE SCAN | IDX_NONPRE | 1 | | 1 (0)| 00:00:01 | 4 | 4 |
-----------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - access("NAME"='OUTLN' AND "ADDRESS"='Y')
Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
5 consistent gets
0 physical reads
0 redo size
610 bytes sent via SQL*Net to client
385 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
7 rows processed
SQL> select /* index(range idx_nonpre)*/ id,name,address from range where name='OUTLN'; --使用索引
21 rows selected.
Execution Plan
----------------------------------------------------------
Plan hash value: 279219031
-----------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | Pstart| Pstop |
-----------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 21 | 672 | 11 (0)| 00:00:01 | | |
| 1 | PARTITION RANGE ALL | | 21 | 672 | 11 (0)| 00:00:01 | 1 | 4 |
| 2 | TABLE ACCESS BY LOCAL INDEX ROWID| RANGE | 21 | 672 | 11 (0)| 00:00:01 | 1 | 4 |
|* 3 | INDEX RANGE SCAN | IDX_NONPRE | 2 | | 5 (0)| 00:00:01 | 1 | 4 |
-----------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - access("NAME"='OUTLN')
Note
-----
- dynamic sampling used for this statement
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
14 consistent gets
0 physical reads
0 redo size
867 bytes sent via SQL*Net to client
396 bytes received via SQL*Net from client
3 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
21 rows processed
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