PostgreSQL 创建表分区

2020年3月14日10:58:48PostgreSQL 创建表分区已关闭评论 393 2345字阅读7分49秒
摘要

在pg里表分区是通过表继承来实现的,一般都是建立一个主表,里面是空,然后每个分区都去继承它。

创建表分区步骤如下:


1. 创建主表
CREATE TABLE users ( uid int not null primary key, name varchar(20));


2. 创建分区表(必须继承上面的主表)

CREATE TABLE users_0 ( check (uid >= 0 and uid< 100) ) INHERITS (users);

CREATE TABLE users_1 ( check (uid >= 100)) INHERITS (users);


3. 在分区表上建立索引,其实这步可以省略的哦

CREATE INDEX users_0_uidindex on users_0(uid);

CREATE INDEX users_1_uidindex on users_1(uid);


4. 创建规则RULE

CREATE RULE users_insert_0 AS

ON INSERT TO users WHERE

(uid >= 0 and uid < 100)

DO INSTEAD

INSERT INTO users_0 VALUES (NEW.uid,NEW.name);

CREATE RULE users_insert_1 AS

ON INSERT TO users WHERE

(uid >= 100)

DO INSTEAD

INSERT INTO users_1 VALUES (NEW.uid,NEW.name);

下面就可以测试写入数据啦:

postgres=# INSERT INTO users VALUES (100,'smallfish');

INSERT 0 0

postgres=# INSERT INTO users VALUES (20,'aaaaa');

INSERT 0 0

postgres=# select * from users;

uid | name

-----+-----------

20 | aaaaa

100 | smallfish

(2 笔资料列)

postgres=# select * from users_0;

uid | name

-----+-------

20 | aaaaa

(1 笔资料列)

postgres=# select * from users_1;

uid | name

-----+-----------

100 | smallfish

(1 笔资料列)

到这里表分区已经可以算完了,不过还有个地方需要修改下,先看count查询把。

postgres=# EXPLAIN SELECT count(*) FROM users where uid<100;

QUERY PLAN

---------------------------------------------------------------------------------------------

Aggregate (cost=62.75..62.76 rows=1 width=0)

-> Append (cost=6.52..60.55 rows=879 width=0)

-> Bitmap Heap Scan on users (cost=6.52..20.18 rows=293 width=0)

Recheck Cond: (uid < 100)

-> Bitmap Index Scan on users_pkey (cost=0.00..6.45 rows=293 width=0)

Index Cond: (uid < 100)

-> Bitmap Heap Scan on users_0 users (cost=6.52..20.18 rows=293 width=0)

Recheck Cond: (uid < 100)

-> Bitmap Index Scan on users_0_uidindex (cost=0.00..6.45 rows=293 width=0)

Index Cond: (uid < 100)

-> Bitmap Heap Scan on users_1 users (cost=6.52..20.18 rows=293 width=0)

Recheck Cond: (uid < 100)

-> Bitmap Index Scan on users_1_uidindex (cost=0.00..6.45 rows=293 width=0)

Index Cond: (uid < 100)

(14 笔资料列)

按照本来想法,uid小于100,理论上应该只是查询users_0表,通过EXPLAIN可以看到其他他扫描了所有分区的表。

postgres=# SET constraint_exclusion = on;

SET

postgres=# EXPLAIN SELECT count(*) FROM users where uid<100;

QUERY PLAN

---------------------------------------------------------------------------------------------

Aggregate (cost=41.83..41.84 rows=1 width=0)

-> Append (cost=6.52..40.37 rows=586 width=0)

-> Bitmap Heap Scan on users (cost=6.52..20.18 rows=293 width=0)

Recheck Cond: (uid < 100)

-> Bitmap Index Scan on users_pkey (cost=0.00..6.45 rows=293 width=0)

Index Cond: (uid < 100)

-> Bitmap Heap Scan on users_0 users (cost=6.52..20.18 rows=293 width=0)

Recheck Cond: (uid < 100)

-> Bitmap Index Scan on users_0_uidindex (cost=0.00..6.45 rows=293 width=0)

Index Cond: (uid < 100)

(10 笔资料列)

到这里整个过程都OK啦!

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