Oracle之range,hash,list分区现实应用及优缺点汇总
引言：Oracle的range,hash,list三大分区可能我们大家在熟悉不过了，但什么每种分区适用于什么场景可能是很多人的疑惑点，那么在选择不同的分区时应该注意什么，为什么这么选，有哪些需要我们加以注意的地方，让我们一一来探索一下吧：）
A.创建range分区，一般用于日期化处理，range分区可以很好的管理基于日期来分区的数据
创建一个新用户ls
SYS@LEO> create user ls identified by ls;
SYS@LEO> grant dba to ls;
SYS@LEO> conn ls/ls
创建样本数据表
create table liusheng (orderid number(10),name varchar2(10),ls_date date);
insert into liusheng values (1,'ls1',to_date('1981-01-02','yyyy-mm-dd'));
insert into liusheng values (1,'ls2',to_date('1998-01-03','yyyy-mm-dd'));
insert into liusheng values (1,'ls3',to_date('1999-01-04','yyyy-mm-dd'));
insert into liusheng values (1,'ls4',to_date('2000-01-05','yyyy-mm-dd'));
insert into liusheng values (1,'ls5',to_date('2000-01-06','yyyy-mm-dd'));
insert into liusheng values (1,'ls6',to_date('2001-01-07','yyyy-mm-dd'));
insert into liusheng values (1,'ls7',to_date('2001-01-08','yyyy-mm-dd'));
insert into liusheng values (1,'ls8',to_date('2002-01-09','yyyy-mm-dd'));
insert into liusheng values (1,'ls9',to_date('2002-01-10','yyyy-mm-dd'));
insert into liusheng values (1,'ls10',to_date('2011-01-11','yyyy-mm-dd'));
创建range分区表
create table liusheng_part
partition by range (ls_date)
(
partition liusheng_part_1999_1 values less than (to_date('1999-01-01','yyyy-mm-dd')) ,
partition liusheng_part_2000_1 values less than (to_date('2000-01-01','yyyy-mm-dd')) ,
partition liusheng_part_2001_1 values less than (to_date('2001-01-01','yyyy-mm-dd')) ,
partition liusheng_part_2002_1 values less than (to_date('2002-01-01','yyyy-mm-dd')) ,
partition liusheng_part_2003_1 values less than (to_date('2003-01-01','yyyy-mm-dd')) ,
partition other values less than (maxvalue)
)
as select * from liusheng;
查看分区
select * from liusheng_part partition (liusheng_part_1999_1);
select * from liusheng_part partition (liusheng_part_2000_1);
select * from liusheng_part partition (liusheng_part_2001_1);
select * from liusheng_part partition (liusheng_part_2002_1);
select * from liusheng_part partition (liusheng_part_2003_1);
select * from liusheng_part partition (other);
B.创建hash分区，利用hash函数打散某列使数据均匀分布，一般用于均衡I/O，缺点数据不容易管理，哈希分区不能DROP、SPLIT 以及MERGE分区
我们创建了拥有10个分区的哈希分区表“LIUSHENG_HASH”
LS@LEO> create table liusheng_hash partition by hash(object_id) partitions 10 as select * from dba_objects;
hash分区所占用的区个数，看每个分区占用的个数都差不多，说明数据还是比较均匀分布的
缺点：hash列上数值不能有太多的重复值，否则会导致数据分布不均匀
select partition_name,count(*) from user_extents where segment_name='LIUSHENG_HASH' group by partition_name;
PARTITION_NAME?????????????????? COUNT(*)
------------------------------ ----------
SYS_P27???????????????????????????????? 3
SYS_P26???????????????????????????????? 3
SYS_P22???????????????????????????????? 2
SYS_P28???????????????????????????????? 3
SYS_P29???????????????????????????????? 2
SYS_P21???????????????????????????????? 2
SYS_P23???????????????????????????????? 3
SYS_P25???????????????????????????????? 3
SYS_P30???????????????????????????????? 2
SYS_P24???????????????????????????????? 3
select count(*) from liusheng_hash;
COUNT(*)
----------
????? 9860
C.创建list分区，一般用于数据可枚举，有限个值，可以考虑列表分区，例如国家名字，按州来分区
创建list分区表，我们按国家来分别存放在不同的州，每个州是一个分区
create table liusheng_list
(city_id NUMBER(5),
city_name VARCHAR2(30),
city_state VARCHAR2(20),
city_amount NUMBER(10)
)
partition by list (city_name)
(
partition? asia VALUES('china','japan'),
partition? europe VALUES ('germany','italy'),
partition? africa VALUES('libya','brazil'),
partition? other? VALUES(DEFAULT)????????????? --默认分区
);
插入数据
insert into liusheng_list values(1,'china','asia',100);
insert into liusheng_list values(2,'germany','europe',101);
insert into liusheng_list values(3,'libya','africa',102);
insert into liusheng_list values(4,'liusheng_city','other',103);
查看数据
LS@LEO> select * from liusheng_list;
?? CITY_ID COUNTRY_NAME?????????????????? STATE??????????????? CITY_AMOUNT
---------- ------------------------------ -------------------- -----------
???????? 1 china?????????????????????????????????????????????? asia???????????????????????? 100
???????? 2 germany????????????????????????????????????? europe?????????????????????? 101
???????? 3 libya???????????????????????????????????????????????? africa?????????????????????? 102
???????? 4 liusheng_city???????????????????????????????? other??????????????????????? 103
小结：测试了上面的三大分区后，我相信现在不仅仅有感性的认识而且也加深了理性的认识，分区是个好东西，合理的利用可以提高我们管理收益（但不一定会提高查询收益），使用不当也会给我们添加许多麻烦，三思而后行是做DBA的一个好习惯。
补充：分区之优势
分区技术实质可以把数据分摊到不同的物理位置，增加I/O负载，提高检索效率。
可用性：分区表可以跨越表空间，而普通表则不然，好处就是如果表的一个分区损坏，其他分区不会受到影响我们只需要修复损坏的分区即
可
