分区索引初步理解

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