分区索引初步理解

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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)----------      1998SQL> 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                       237OUTLN                         21SYS                         2739SQL> set autot traceonlySQL>  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 statementStatistics----------------------------------------------------------          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 processedSQL>  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 statementStatistics----------------------------------------------------------          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 processedSQL> 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 statementStatistics----------------------------------------------------------          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 processedSQL>  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 statementStatistics----------------------------------------------------------          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 processedSQL> 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 statementStatistics----------------------------------------------------------          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 processedSQL>  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 statementStatistics----------------------------------------------------------          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