PostgreSQL 11 preview - 分区表用法及增强 - 增加HASH分区支持 (hash, range, list)

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背景

PostgreSQL 10开始内置分区表的功能，11对分区表进行了增强，包括：

1、增加HASH分区的支持，支持了RANGE, HASH, LIST三种分区。

https://www.postgresql.org/docs/devel/static/ddl-partitioning.html

2、支持分区表的INSERT ON CONFLICT

https://www.postgresql.org/docs/devel/static/sql-insert.html

3、支持分区表的全局索引管理

《PostgreSQL 11 preview - 新功能, 分区表全局索引管理》

4、支持分区表的并行分区JOIN

《PostgreSQL 11 preview - 分区表智能并行JOIN (已类似MPP架构，性能暴增)》

分区表定义例子

https://www.postgresql.org/docs/devel/static/sql-createtable.html

range 分区表

1、单列range

CREATE TABLE measurement (    
    logdate         date not null,    
    peaktemp        int,    
    unitsales       int    
) PARTITION BY RANGE (logdate);    

CREATE TABLE measurement_y2016m07    
    PARTITION OF measurement (    
    unitsales DEFAULT 0    
) FOR VALUES FROM ('2016-07-01') TO ('2016-08-01');    

2、多列RANGE

CREATE TABLE measurement_year_month (    
    logdate         date not null,    
    peaktemp        int,    
    unitsales       int    
) PARTITION BY RANGE (EXTRACT(YEAR FROM logdate), EXTRACT(MONTH FROM logdate));    

CREATE TABLE measurement_ym_older    
    PARTITION OF measurement_year_month    
    FOR VALUES FROM (MINVALUE, MINVALUE) TO (2016, 11);    
    
CREATE TABLE measurement_ym_y2016m11    
    PARTITION OF measurement_year_month    
    FOR VALUES FROM (2016, 11) TO (2016, 12);    
    
CREATE TABLE measurement_ym_y2016m12    
    PARTITION OF measurement_year_month    
    FOR VALUES FROM (2016, 12) TO (2017, 01);    
    
CREATE TABLE measurement_ym_y2017m01    
    PARTITION OF measurement_year_month    
    FOR VALUES FROM (2017, 01) TO (2017, 02);    

list 分区表

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

CREATE TABLE cities_ab    
    PARTITION OF cities (    
    CONSTRAINT city_id_nonzero CHECK (city_id != 0)    
) FOR VALUES IN ('a', 'b');    

如果想定义多级分区，那么在创建分区表时，也使用partition by即可

CREATE TABLE cities_ab    
    PARTITION OF cities (    
    CONSTRAINT city_id_nonzero CHECK (city_id != 0)    
) FOR VALUES IN ('a', 'b') PARTITION BY RANGE (population);    
    
    
CREATE TABLE cities_ab_10000_to_100000    
    PARTITION OF cities_ab FOR VALUES FROM (10000) TO (100000);    

hash 分区表

CREATE TABLE orders (    
    order_id     bigint not null,    
    cust_id      bigint not null,    
    status       text    
) PARTITION BY HASH (order_id);    

CREATE TABLE orders_p1 PARTITION OF orders    
    FOR VALUES WITH (MODULUS 4, REMAINDER 0);    
CREATE TABLE orders_p2 PARTITION OF orders    
    FOR VALUES WITH (MODULUS 4, REMAINDER 1);    
CREATE TABLE orders_p3 PARTITION OF orders    
    FOR VALUES WITH (MODULUS 4, REMAINDER 2);    
CREATE TABLE orders_p4 PARTITION OF orders    
    FOR VALUES WITH (MODULUS 4, REMAINDER 3);    

默认分区

CREATE TABLE cities_partdef    
    PARTITION OF cities DEFAULT;    

小结

PostgreSQL的分区表非常灵活，

1、可以按单列或多列分区

2、可以按表达式分区

3、可以创建多级分区（不限级数）

多级分区定义例子

1、创建主表

create table t_range_list(id int, info text, crt_time timestamp) partition by list ( mod(hashtext(info), 4) );      

2、创建一级分区，主表

create table t_range_list_0 partition of t_range_list (id  , info , crt_time ) for values in (0) partition by range (crt_time);      
create table t_range_list_1 partition of t_range_list (id  , info , crt_time ) for values in (1) partition by range (crt_time);      
create table t_range_list_2 partition of t_range_list (id  , info , crt_time ) for values in (2) partition by range (crt_time);      
create table t_range_list_3 partition of t_range_list (id  , info , crt_time ) for values in (3) partition by range (crt_time);      

3、创建2级分区表

create table t_range_list_0_201611 partition of t_range_list_0 (id  primary key, info , crt_time ) for values from ('2016-10-01') to ('2016-11-01');      
create table t_range_list_0_201612 partition of t_range_list_0 (id  primary key, info , crt_time ) for values from ('2016-11-01') to ('2016-12-01');      
      
create table t_range_list_1_201611 partition of t_range_list_1 (id  primary key, info , crt_time ) for values from ('2016-10-01') to ('2016-11-01');      
create table t_range_list_1_201612 partition of t_range_list_1 (id  primary key, info , crt_time ) for values from ('2016-11-01') to ('2016-12-01');      
      
create table t_range_list_2_201611 partition of t_range_list_2 (id  primary key, info , crt_time ) for values from ('2016-10-01') to ('2016-11-01');      
create table t_range_list_2_201612 partition of t_range_list_2 (id  primary key, info , crt_time ) for values from ('2016-11-01') to ('2016-12-01');      
      
create table t_range_list_3_201611 partition of t_range_list_3 (id  primary key, info , crt_time ) for values from ('2016-10-01') to ('2016-11-01');      
create table t_range_list_3_201612 partition of t_range_list_3 (id  primary key, info , crt_time ) for values from ('2016-11-01') to ('2016-12-01');      

绑定和解绑分区

1、绑定分区，指将已有的普通表，绑定到某个分区表下面，作为它的一个分区，绑定分区时，需要指定分区的区间。

ALTER TABLE [ IF EXISTS ] name    
    ATTACH PARTITION partition_name { FOR VALUES partition_bound_spec | DEFAULT }    

2、解绑分区，指将某个分区从现有的分区表中摘除。

ALTER TABLE [ IF EXISTS ] name    
    DETACH PARTITION partition_name    

例如某个分区已经不怎么查到了，那么可以解绑，并使用DDL把它MOVE一个冷存储的表空间里面。(如果是阿里云RDS PG，那么可以MOVE到OSS里面)

绑定

1、将measurement_y2016m07普通表绑定到measurement。指定它的分区定义取值范围。

Attach a partition to range partitioned table:

ALTER TABLE measurement    
    ATTACH PARTITION measurement_y2016m07 FOR VALUES FROM ('2016-07-01') TO ('2016-08-01');    

2、将cities_ab普通表绑定到cities。指定它的分区定义取值范围。

Attach a partition to list partitioned table:

ALTER TABLE cities    
    ATTACH PARTITION cities_ab FOR VALUES IN ('a', 'b');    

3、将cities_partdef普通表绑定到cities。并设置为默认分区。

Attach a default partition to a partitioned table:

ALTER TABLE cities    
    ATTACH PARTITION cities_partdef DEFAULT;    

3、将orders_p4普通表绑定到orders。指定它的分区定义取值范围。

Attach a partition to hash partitioned table:

ALTER TABLE orders    
    ATTACH PARTITION orders_p4 FOR VALUES WITH (MODULUS 4, REMAINDER 3);    

解绑

1、将分区measurement_y2015m12从measurement中摘除。

Detach a partition from partitioned table:

ALTER TABLE measurement    
    DETACH PARTITION measurement_y2015m12;    

分区表 insert on conflict 例子

CREATE TABLE orders (    
    order_id     bigint not null,    
    cust_id      bigint not null,    
    status       text    
) PARTITION BY HASH (order_id);    

CREATE TABLE orders_p1 PARTITION OF orders (order_id primary key)     
    FOR VALUES WITH (MODULUS 4, REMAINDER 0);    
    
CREATE TABLE orders_p2 PARTITION OF orders (order_id primary key)     
    FOR VALUES WITH (MODULUS 4, REMAINDER 1);    
    
CREATE TABLE orders_p3 PARTITION OF orders (order_id primary key)     
    FOR VALUES WITH (MODULUS 4, REMAINDER 2);    
    
CREATE TABLE orders_p4 PARTITION OF orders (order_id primary key)     
    FOR VALUES WITH (MODULUS 4, REMAINDER 3);    

postgres=# insert into orders values (1,1,'test') on conflict (order_id) do nothing;    
    
ERROR:  there is no unique or exclusion constraint matching the ON CONFLICT specification    

语法层面已支持分区表的insert on conflict，接下来就等提交分区表UK索引的PATCH。

https://commitfest.postgresql.org/16/1452/