PostgreSQL 11 新特性之分区索引_sql

概述PostgreSQL 11 支持基于分区表创建索引，并且自动为每个分区创建具有相同属性的索引。PostgreSQL 11 还支持分区表上的唯一约束（主键和唯一键）。

文章目录分区自动索引分区表唯一约束

在 Postgresql 10 中，分区上的索引需要基于各个分区手动创建，而不能基于分区的父表创建索引。Postgresql 11 可以基于分区表创建索引。分区表上的索引并不会创建一个物理上的索引，而是为每个分区上的索引创建一个模板。

分区自动索引

如果在分区表上创建了一个索引，Postgresql 自动为每个分区创建具有相同属性的索引。

CREATE table measurement (    city_ID         int not @H_403_36@null,    logdate         date not @H_403_36@null,    peaktemp        int,    unitsales       int) PARTITION BY RANGE (logdate);CREATE table measurement_y2018 PARTITION OF measurement    FOR VALUES FROM ('2018-01-01') TO ('2019-01-01');CREATE table measurement_y2019 PARTITION OF measurement    FOR VALUES FROM ('2019-01-01') TO ('2020-01-01');CREATE INDEX IDx_measurement_peaktemp ON measurement(peaktemp);\d measurement              table "public.measurement"  Column   |  Type   | Collation | Nullable | Default -----------+---------+-----------+----------+--------- city_ID   | integer |           | not @H_403_36@null |  logdate   | date    |           | not @H_403_36@null |  peaktemp  | integer |           |          |  unitsales | integer |           |          | Partition key: RANGE (logdate)Indexes:    "IDx_measurement_peaktemp" btree (peaktemp)Number of partitions: 2 (Use \d+ to List them.)

measurement 表上创建了一个索引 IDx_measurement_peaktemp，因此该表上的分区也会自动创建相应的索引。

\d measurement_y2018           table "public.measurement_y2018"  Column   |  Type   | Collation | Nullable | Default -----------+---------+-----------+----------+--------- city_ID   | integer |           | not @H_403_36@null |  logdate   | date    |           | not @H_403_36@null |  peaktemp  | integer |           |          |  unitsales | integer |           |          | Partition of: measurement FOR VALUES FROM ('2018-01-01') TO ('2019-01-01')Indexes:    "measurement_y2018_peaktemp_IDx" btree (peaktemp)

自动创建的索引，名称按照 “{partition name}_{column name}_IDx” 的模式定义。多个字段的复合索引使用下划线（_）连接字段名称。如果索引名称已经存在，在名称的最后添加一个数字。如果名称过长，使用缩写。

随后新增的分区或者通过 ATTACH PARTITION 挂载的分区都会自动创建相应的索引。

CREATE table measurement_y2020 (liKE measurement);ALTER table measurement ATTACH PARTITION measurement_y2020  FOR VALUES FROM ('2020-01-01') TO ('2021-01-01');\d measurement_y2020           table "public.measurement_y2020"  Column   |  Type   | Collation | Nullable | Default -----------+---------+-----------+----------+--------- city_ID   | integer |           | not @H_403_36@null |  logdate   | date    |           | not @H_403_36@null |  peaktemp  | integer |           |          |  unitsales | integer |           |          | Partition of: measurement FOR VALUES FROM ('2020-01-01') TO ('2021-01-01')Indexes:    "measurement_y2020_peaktemp_IDx" btree (peaktemp)

自动创建的索引不能单独删除，可以通过分区表统一删除。

DROP INDEX measurement_y2020_peaktemp_IDx;ERROR:  cannot drop index measurement_y2020_peaktemp_IDx because index IDx_measurement_peaktemp requires itHINT:  You can drop index IDx_measurement_peaktemp instead.DROP INDEX IDx_measurement_peaktemp;

分区表唯一约束

对于 Postgresql 10，只能基于分区创建唯一约束（PRIMARY KEY 和 UNIQUE KEY），而不能针对分区的父表创建唯一约束。Postgresql 11 支持分区表上的唯一约束。

CREATE table rtable(c1 INT, c2 VARCHAR(10)) PARTITION BY RANGE(c1);ALTER table rtable ADD CONSTRAINT pk_rtable PRIMARY KEY(c1);\d rtable                      table "public.rtable" Column |         Type          | Collation | Nullable | Default --------+-----------------------+-----------+----------+--------- c1     | integer               |           | not @H_403_36@null |  c2     | character varying(10) |           |          | Partition key: RANGE (c1)Indexes:    "pk_rtable" PRIMARY KEY, btree (c1)Number of partitions: 0

添加分区或者加载（ATTACH）分区时自动创建相应的主键：

CREATE table rtable100 PARTITION OF rtable FOR VALUES FROM (1) TO (100);\d rtable100                    table "public.rtable100" Column |         Type          | Collation | Nullable | Default --------+-----------------------+-----------+----------+--------- c1     | integer               |           | not @H_403_36@null |  c2     | character varying(10) |           |          | Partition of: rtable FOR VALUES FROM (1) TO (100)Indexes:    "rtable100_pkey" PRIMARY KEY, btree (c1)

如果在分区表上创建了唯一约束，无法再创建基于外部表（FOREIGN table）的分区。因为无法为外部表创建唯一约束。

CREATE FOREIGN table rtable200 PARTITION OF rtable FOR VALUES FROM (101) TO (200) SERVER remote1;ERROR:  cannot create index on foreign table "rtable200"

主键约束或唯一约束必须包含分区字段。这样才能确保整个分区表内的唯一性，因为每个分区上的唯一约束只维护自身的唯一性。

CREATE table rtable1(c1 INT, c2 VARCHAR(10)) PARTITION BY RANGE(c1);ALTER table rtable1 ADD CONSTRAINT pk_table1 PRIMARY KEY(c2);ERROR:  insufficIEnt columns in PRIMARY KEY constraint deFinitionDETAIL:  PRIMARY KEY constraint on table "rtable1" lacks column "c1" which is part of the partition key.