PostgreSQL 11中分区表的本地索引

在PostgreSQL 10中引入了声明式分区时，这是向前迈出的一大步。 但是，新的重要功能在PostgreSQL 10中不起作用，而现在在PostgreSQL 11中已解决。其中之一是本地分区索引。 为了更容易理解，我们从PostgreSQL 10中的示例开始。

postgresql 10：

postgres=# select version();
                                                 version                                                  
----------------------------------------------------------------------------------------------------------
 PostgreSQL 10.14 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-39), 64-bit
(1 row)

postgres=# create table part ( a int, list varchar(5) ) partition by list (list);
CREATE TABLE
postgres=# create table part_1 partition of part for values in ('beer');
CREATE TABLE
postgres=# create table part_2 partition of part for values in ('wine');
CREATE TABLE
postgres=# d+ part
                                          Table "public.part"
 Column |         Type         | Collation | Nullable | Default | Storage  | Stats target | Description 
--------+----------------------+-----------+----------+---------+----------+--------------+-------------
 a      | integer              |           |          |         | plain    |              | 
 list   | character varying(5) |           |          |         | extended |              | 
Partition key: LIST (list)
Partitions: part_1 FOR VALUES IN ('beer'),
            part_2 FOR VALUES IN ('wine')

postgres=# 

在ppstgresql 10中，如果在分区表上创建索引，会发生什么呢？

postgres=# create index idx_test on part (a);
ERROR:  cannot create index on partitioned table "part"
postgres=# 

无法创建索引。但是可以在分区上创建索引：

postgres=# create index idx_test_1 on part_1 (a);
CREATE INDEX
postgres=# create index idx_test_2 on part_2 (a);
CREATE INDEX
postgres=# 

再来看看postgresql 11中是什么样子的。

postgres=# create table part ( a int, list varchar(5) ) partition by list (list);
CREATE TABLE
postgres=# create table part_1 partition of part for values in ('beer');
CREATE TABLE
postgres=# create table part_2 partition of part for values in ('wine');
CREATE TABLE
postgres=# d+ part
                                          Table "public.part"
 Column |         Type         | Collation | Nullable | Default | Storage  | Stats target | Description 
--------+----------------------+-----------+----------+---------+----------+--------------+-------------
 a      | integer              |           |          |         | plain    |              | 
 list   | character varying(5) |           |          |         | extended |              | 
Partition key: LIST (list)
Partitions: part_1 FOR VALUES IN ('beer'),
            part_2 FOR VALUES IN ('wine')

postgres=# 

再次尝试在分区表上创建索引：

postgres=# create index idx_test on part (a);
CREATE INDEX
postgres=# d+ part
                                          Table "public.part"
 Column |         Type         | Collation | Nullable | Default | Storage  | Stats target | Description 
--------+----------------------+-----------+----------+---------+----------+--------------+-------------
 a      | integer              |           |          |         | plain    |              | 
 list   | character varying(5) |           |          |         | extended |              | 
Partition key: LIST (list)
Indexes:
    "idx_test" btree (a)
Partitions: part_1 FOR VALUES IN ('beer'),
            part_2 FOR VALUES IN ('wine')

postgres=# d+ part_1
                                         Table "public.part_1"
 Column |         Type         | Collation | Nullable | Default | Storage  | Stats target | Description 
--------+----------------------+-----------+----------+---------+----------+--------------+-------------
 a      | integer              |           |          |         | plain    |              | 
 list   | character varying(5) |           |          |         | extended |              | 
Partition of: part FOR VALUES IN ('beer')
Partition constraint: ((list IS NOT NULL) AND ((list)::text = 'beer'::character varying(5)))
Indexes:
    "part_1_a_idx" btree (a)

postgres=# d+ part_2
                                         Table "public.part_2"
 Column |         Type         | Collation | Nullable | Default | Storage  | Stats target | Description 
--------+----------------------+-----------+----------+---------+----------+--------------+-------------
 a      | integer              |           |          |         | plain    |              | 
 list   | character varying(5) |           |          |         | extended |              | 
Partition of: part FOR VALUES IN ('wine')
Partition constraint: ((list IS NOT NULL) AND ((list)::text = 'wine'::character varying(5)))
Indexes:
    "part_2_a_idx" btree (a)

postgres=# 

在postgresql 11中，分区表上创建的索引被级联到了分区上。

 

此外，在postgresql10中，如果想对分区表添加主键约束，会失败：

postgres=# alter table part add constraint part_pk primary key(a,list);
ERROR:  primary key constraints are not supported on partitioned tables
LINE 1: alter table part add constraint part_pk primary key(a,list);
                             ^
postgres=# 

不过，却可以在分区上添加主键约束：

postgres=# alter table part_1 add constraint part1_pk primary key(a,list);
ALTER TABLE
postgres=# alter table part_2 add constraint part2_pk primary key(a,list);
ALTER TABLE
postgres=# 

　　

在postgresql11中，可以直接在分区表上添加主键约束，添加成功后，会自动添加到分区上：

postgres=# alter table part add constraint part_pk primary key(a,list);
ALTER TABLE
postgres=# d+ part_1
                                         Table "public.part_1"
 Column |         Type         | Collation | Nullable | Default | Storage  | Stats target | Description
--------+----------------------+-----------+----------+---------+----------+--------------+-------------
 a      | integer              |           | not null |         | plain    |              |
 list   | character varying(5) |           | not null |         | extended |              |
Partition of: part FOR VALUES IN ('beer')
Partition constraint: ((list IS NOT NULL) AND ((list)::text = 'beer'::character varying(5)))
Indexes:
    "part_1_pkey" PRIMARY KEY, btree (a, list)
    "part_1_a_idx" btree (a)

postgres=# d+ part_2
                                         Table "public.part_2"
 Column |         Type         | Collation | Nullable | Default | Storage  | Stats target | Description
--------+----------------------+-----------+----------+---------+----------+--------------+-------------
 a      | integer              |           | not null |         | plain    |              |
 list   | character varying(5) |           | not null |         | extended |              |
Partition of: part FOR VALUES IN ('wine')
Partition constraint: ((list IS NOT NULL) AND ((list)::text = 'wine'::character varying(5)))
Indexes:
    "part_2_pkey" PRIMARY KEY, btree (a, list)
    "part_2_a_idx" btree (a)

postgres=# d+ part
                                          Table "public.part"
 Column |         Type         | Collation | Nullable | Default | Storage  | Stats target | Description
--------+----------------------+-----------+----------+---------+----------+--------------+-------------
 a      | integer              |           | not null |         | plain    |              |
 list   | character varying(5) |           | not null |         | extended |              |
Partition key: LIST (list)
Indexes:
    "part_pk" PRIMARY KEY, btree (a, list)
    "idx_test" btree (a)
Partitions: part_1 FOR VALUES IN ('beer'),
            part_2 FOR VALUES IN ('wine')

postgres=#

当然也可以像10那样，直接在分区上添加主键约束。

不过，在分区表上添加的主键约束，必须包含分区列：

postgres=# alter table part add constraint part_pk primary key(a);
ERROR:  insufficient columns in PRIMARY KEY constraint definition
DETAIL:  PRIMARY KEY constraint on table "part" lacks column "list" which is part of the partition key.
postgres=#