PostgreSQL 12: 新增 pg_partition_tree() 函数显示分区表信息

PostgreSQL 12 新增三个分区查询函数,如下:

  • pg_partition_tree(regclass): 返回分区表详细信息,例如分区名称、上一级分区名称、是否叶子结点、层级,层级 0 表示顶层父表。
  • pg_partition_ancestors(regclass): 返回上层分区名称,包括本层分区名称。
  • pg_partition_root(regclass): 返回顶层父表名称。

发行说明

Add partition introspection functions (Michaël Paquier, Álvaro Herrera, Amit Langote)

New function pg_partition_root() returns the top-most parent of a partition tree, pg_partition_ancestors() reports all ancestors of a partition, and pg_partition_tree() displays information about partitions.

环境准备: 创建二维分区表

创建父表,如下:

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CREATE TABLE userinfo (
userid int4,
username character varying(64),
ctime timestamp(6) without time zone
) PARTITION BY HASH(userid);

创建第一层分区,如下:

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CREATE TABLE userinfo_p0 PARTITION OF userinfo FOR VALUES WITH(MODULUS 4, REMAINDER 0) PARTITION BY RANGE(ctime);
CREATE TABLE userinfo_p1 PARTITION OF userinfo FOR VALUES WITH(MODULUS 4, REMAINDER 1);
CREATE TABLE userinfo_p2 PARTITION OF userinfo FOR VALUES WITH(MODULUS 4, REMAINDER 2);
CREATE TABLE userinfo_p3 PARTITION OF userinfo FOR VALUES WITH(MODULUS 4, REMAINDER 3);

创建第二层分区,如下:

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CREATE TABLE userinfo_p0_old PARTITION OF userinfo_p0 FOR VALUES FROM (MINVALUE) TO ('2019-06-01');
CREATE TABLE userinfo_p0_201906 PARTITION OF userinfo_p0 FOR VALUES FROM ('2019-06-01') TO ('2019-07-01');
CREATE TABLE userinfo_p0_201907 PARTITION OF userinfo_p0 FOR VALUES FROM ('2019-07-01') TO ('2019-08-01');

使用元命令查看分区表信息,如下:

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mydb=> \d+ userinfo
Partitioned table "pguser.userinfo"
Column | Type | Collation | Nullable | Default | Storage | Stats target | Description
----------+--------------------------------+-----------+----------+---------+----------+--------------+-------------
userid | integer | | | | plain | |
username | character varying(64) | | | | extended | |
ctime | timestamp(6) without time zone | | | | plain | |
Partition key: HASH (userid)
Partitions: userinfo_p0 FOR VALUES WITH (modulus 4, remainder 0), PARTITIONED,
userinfo_p1 FOR VALUES WITH (modulus 4, remainder 1),
userinfo_p2 FOR VALUES WITH (modulus 4, remainder 2),
userinfo_p3 FOR VALUES WITH (modulus 4, remainder 3)

备注:以上可以查看到分区表大部分信息,但二级分区的信息并没有显示,userinfo_p0 这行只显示 PARTITIONED,没有列出二级分区信息。

若想查看二级分区信息,如下:

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mydb=> \d+ userinfo_p0
Partitioned table "pguser.userinfo_p0"
Column | Type | Collation | Nullable | Default | Storage | Stats target | Description
----------+--------------------------------+-----------+----------+---------+----------+--------------+-------------
userid | integer | | | | plain | |
username | character varying(64) | | | | extended | |
ctime | timestamp(6) without time zone | | | | plain | |
Partition of: userinfo FOR VALUES WITH (modulus 4, remainder 0)
Partition constraint: satisfies_hash_partition('16432'::oid, 4, 0, userid)
Partition key: RANGE (ctime)
Partitions: userinfo_p0_201906 FOR VALUES FROM ('2019-06-01 00:00:00') TO ('2019-07-01 00:00:00'),
userinfo_p0_201907 FOR VALUES FROM ('2019-07-01 00:00:00') TO ('2019-08-01 00:00:00'),
userinfo_p0_old FOR VALUES FROM (MINVALUE) TO ('2019-06-01 00:00:00')

pg_partition_tree 函数

使用 pg_partition_tree() 函数查看分区表信息,如下:

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mydb=>  SELECT * FROM pg_partition_tree('userinfo');
relid | parentrelid | isleaf | level
--------------------+-------------+--------+-------
userinfo | | f | 0
userinfo_p0 | userinfo | f | 1
userinfo_p1 | userinfo | t | 1
userinfo_p2 | userinfo | t | 1
userinfo_p3 | userinfo | t | 1
userinfo_p0_201906 | userinfo_p0 | t | 2
userinfo_p0_201907 | userinfo_p0 | t | 2
userinfo_p0_old | userinfo_p0 | t | 2
(8 rows)

备注: pg_partition_tree() 函数列出了分区表的所有分区、上一级分区、是否是叶子节点、当前分区所处层级信息。

pg_partition_ancestors 函数

pg_partition_ancestors 函数返回上层分区名称,包括本层分区名称,如下:

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mydb=> SELECT pg_partition_ancestors('userinfo_p0');
pg_partition_ancestors
------------------------
userinfo_p0
userinfo
(2 rows)

pg_partition_root 函数

pg_partition_root()函数返回最顶层父表名称,如下:

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mydb=> SELECT pg_partition_root('userinfo_p0_201907');
pg_partition_root
-------------------
userinfo
(1 row)

验证数据分布

最后验证二维分区表 userinfo 数据分布,插入测试数据,如下:

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INSERT INTO userinfo(userid,username,ctime) SELECT n, n || '_username',now() FROM generate_series(1,8) n;
INSERT INTO userinfo(userid,username,ctime) SELECT n, n || '_username',now() - interval ' 2 months 'FROM generate_series(1,8) n;

验证数据分布,如下:

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mydb=> \dt+ userinfo*
List of relations
Schema | Name | Type | Owner | Size | Description
--------+--------------------+-------------------+--------+------------+-------------
pguser | userinfo | partitioned table | pguser | 0 bytes |
pguser | userinfo_p0 | partitioned table | pguser | 0 bytes |
pguser | userinfo_p0_201906 | table | pguser | 8192 bytes |
pguser | userinfo_p0_201907 | table | pguser | 0 bytes |
pguser | userinfo_p0_old | table | pguser | 8192 bytes |
pguser | userinfo_p1 | table | pguser | 8192 bytes |
pguser | userinfo_p2 | table | pguser | 8192 bytes |
pguser | userinfo_p3 | table | pguser | 8192 bytes |
(8 rows)

根据表大小初步判读仅底层分区存储数据。

查看二级分区数据分布上,如下:

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mydb=> SELECT * FROM userinfo_p0;
userid | username | ctime
--------+------------+----------------------------
1 | 1_username | 2019-05-16 09:36:18.83122
1 | 1_username | 2019-07-16 09:36:18.825426
(2 rows)

查看三级分区数据分布,如下:

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mydb=> SELECT * FROM userinfo_p0_201907;
userid | username | ctime
--------+------------+----------------------------
1 | 1_username | 2019-07-16 09:36:18.825426
(1 row)

mydb=> SELECT * FROM userinfo_p0_201906;
userid | username | ctime
--------+----------+-------
(0 rows)

mydb=> SELECT * FROM userinfo_p0_old;
userid | username | ctime
--------+------------+---------------------------
1 | 1_username | 2019-05-16 09:36:18.83122

总结

对于一维分区表,PostgreSQL 提供的元命令足够查看分区的完整信息,但对于多维分区表,元命令无法查看详尽的分区信息,PostgreSQL 12 提供的分区函数很容易做到这点。

尽管二维分区表的使用并不是很多,分区表函数提供了分区表查询的另一种途径。

参考

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