Oracle 分区索引初步理解
Oracle 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
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