PostgreSQL 10 版本已支持分区表，但不支持分区表根据分区键UPDATE记录，PostgreSQL 11 版本这方面得到增加，当分区表的分区键字段被UPDATE后，会自动将该记录转移至新的分区中。

官网Release说明如下：

UPDATE statements that change a partition key now move affected rows to the appropriate partitions

本文以UPDATE列表分区表分区键为例进行演示。

测试环境准备

创建列表分区表并插入测试数据，为演示做准备。

创建父表

CREATE TABLE cities (
    city_id      bigserial not null,
    name         text not null,
    population   bigint
) PARTITION BY LIST (left(lower(name), 1));

创建子表

CREATE TABLE cities_a PARTITION OF cities ( CONSTRAINT city_id_nonzero CHECK (city_id != 0)) FOR VALUES IN ('a');
CREATE TABLE cities_b PARTITION OF cities ( CONSTRAINT city_id_nonzero CHECK (city_id != 0)) FOR VALUES IN ('b');
CREATE TABLE cities_c PARTITION OF cities ( CONSTRAINT city_id_nonzero CHECK (city_id != 0)) FOR VALUES IN ('c');

插入测试数据

INSERT INTO cities(city_id,name,population) VALUES (1,'a_city','100000');
INSERT INTO cities(city_id,name,population) VALUES (2,'b_city','200000');
INSERT INTO cities(city_id,name,population) VALUES (3,'c_city','300000');

PostgreSQL 10 测试

PostgreSQL 10 版本UPDATE分区键报错，如下：

mydb=> SELECT version();
                                                 version
---------------------------------------------------------------------------------------------------------
 PostgreSQL 10.0 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-11), 64-bit
(1 row)


mydb=> UPDATE cities SET name='ca_city' WHERE city_id=1;
ERROR:  new row for relation "cities_a" violates partition constraint
DETAIL:  Failing row contains (1, ca_city, 100000).

PostgreSQL 11 测试

PostgreSQL 11 版本支持更新分区键，如下:

francs=> SELECT version();
                                                  version
------------------------------------------------------------------------------------------------------------
 PostgreSQL 11beta3 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-11), 64-bit
(1 row)

francs=> UPDATE cities SET name='ca_city' WHERE city_id=1;
UPDATE 1

francs=> SELECT * FROM cities;
 city_id |  name   | population
---------+---------+------------
       2 | b_city  |     200000
       3 | c_city  |     300000
       1 | ca_city |     100000
(3 rows)

查看cities_c分区，发现city_id为1的记录已转移到此分区，如下：

francs=> SELECT * from cities_c;
 city_id |  name   | population
---------+---------+------------
       3 | c_city  |     300000
       1 | ca_city |     100000
(2 rows)

参考

• PostgreSQL10: 重量级新特性-支持分区表
• PostgreSQL11: 分区表增加哈希分区
• PostgreSQL11: 分区表支持创建主键、外键、索引
• PostgreSQL11: 分区表支持UPDATE分区键
• PostgreSQL11: 分区表增加 Default Partition
• PostgreSQL11: Partitioning Improvements

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