这篇文章主要介绍“PostgreSQL12的pg_partition_tree和pg_partition_root系统函数有什么作用”，在日常操作中，相信很多人在PostgreSQL12的pg_partition_tree和pg_partition_root系统函数有什么作用问题上存在疑惑，小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答”PostgreSQL12的pg_partition_tree和pg_partition_root系统函数有什么作用”的疑惑有所帮助！接下来，请跟着小编一起来学习吧！
在PG 12以前的版本,获取分区表中的分区以及子分区等信息需要使用递归CTE查询脚本来获取,不直观而且麻烦,在PG 12中新增了pg_partition_tree和pg_partition_root系统函数分别用于获取分区树和分区的root relation.
下面以一个简单的例子进行说明.
测试脚本
-- Hash Partition
drop table if exists t_hash2;
create table t_hash2 (c1 int not null,c2 varchar(40),c3 varchar(40)) partition by hash(c1);
-- Level 1
create table t_hash2_1 partition of t_hash2 for values with (modulus 6,remainder 0) partition by hash(c1);
create table t_hash2_2 partition of t_hash2 for values with (modulus 6,remainder 1) partition by hash(c1);
create table t_hash2_3 partition of t_hash2 for values with (modulus 6,remainder 2);
create table t_hash2_4 partition of t_hash2 for values with (modulus 6,remainder 3);
create table t_hash2_5 partition of t_hash2 for values with (modulus 6,remainder 4);
create table t_hash2_6 partition of t_hash2 for values with (modulus 6,remainder 5);
-- Level 2
create table t_hash2_1_1 partition of t_hash2_1 for values with (modulus 2,remainder 0);
create table t_hash2_1_2 partition of t_hash2_1 for values with (modulus 2,remainder 1);
create table t_hash2_2_1 partition of t_hash2_2 for values with (modulus 2,remainder 0);
create table t_hash2_2_2 partition of t_hash2_2 for values with (modulus 2,remainder 1);t_hash2是一张Hash分区表,有6个子分区,其中子分区中的t_hash2_1和t_hash2_2也是分区表,分别有2个分区.
在PG 11中,需要使用CTE递归查询来查询该分区的相关信息:
-- PG11
WITH RECURSIVE partition_info
(relid, -- oid
relname, -- 名称
relsize, -- 大小
relispartition, -- 是否分区表
relkind) AS (
SELECT oid AS relid,
relname,
pg_relation_size(oid) AS relsize,
relispartition,
relkind
FROM pg_catalog.pg_class
WHERE relname = 't_hash2' AND -- 最顶层的分区表
relkind = 'p'
UNION ALL
SELECT
c.oid AS relid,
c.relname AS relname,
pg_relation_size(c.oid) AS relsize,
c.relispartition AS relispartition,
c.relkind AS relkind
FROM partition_info AS p,
pg_catalog.pg_inherits AS i,
pg_catalog.pg_class AS c
WHERE p.relid = i.inhparent AND -- 从最顶层的分区表(即t_hash2)开始递归
c.oid = i.inhrelid AND -- 寻找子分区
c.relispartition -- 分区表标记
)
SELECT * FROM partition_info;
relid | relname | relsize | relispartition | relkind
-------+-------------+---------+----------------+---------
57457 | t_hash2 | 0 | f | p
57466 | t_hash2_3 | 0 | t | r
57469 | t_hash2_4 | 0 | t | r
57472 | t_hash2_5 | 0 | t | r
57475 | t_hash2_6 | 0 | t | r
57460 | t_hash2_1 | 0 | t | p
57463 | t_hash2_2 | 0 | t | p
57487 | t_hash2_2_2 | 0 | t | r
57478 | t_hash2_1_1 | 0 | t | r
57481 | t_hash2_1_2 | 0 | t | r
57484 | t_hash2_2_1 | 0 | t | r
(11 rows)而在PG 12中,则可以直接使用系统函数获取相关信息:
testdb=# \sf pg_partition_tree
CREATE OR REPLACE FUNCTION pg_catalog.pg_partition_tree(rootrelid regclass, OUT relid regclass, OUT parentrelid regclass, OUT isleaf boolean, OUT level integer)
RETURNS SETOF record
LANGUAGE internal
PARALLEL SAFE STRICT
AS $function$pg_partition_tree$function$
testdb=# select pg_partition_tree('t_hash2');
pg_partition_tree
-----------------------------
(t_hash2,,f,0)
(t_hash2_1,t_hash2,f,1)
(t_hash2_2,t_hash2,f,1)
(t_hash2_3,t_hash2,t,1)
(t_hash2_4,t_hash2,t,1)
(t_hash2_5,t_hash2,t,1)
(t_hash2_6,t_hash2,t,1)
(t_hash2_1_1,t_hash2_1,t,2)
(t_hash2_1_2,t_hash2_1,t,2)
(t_hash2_2_1,t_hash2_2,t,2)
(t_hash2_2_2,t_hash2_2,t,2)
(11 rows)返回的信息包括:
relid -> 该分区的relid
parentrelid -> 父分区
isleaf —> 是否叶子节点
level —> 层次
通过pg_partition_root可以获取分区表的root节点
testdb=# \sf pg_partition_root
CREATE OR REPLACE FUNCTION pg_catalog.pg_partition_root(regclass)
RETURNS regclass
LANGUAGE internal
IMMUTABLE PARALLEL SAFE STRICT
AS $function$pg_partition_root$function$
testdb=# select pg_partition_root('t_hash2_2_2');
pg_partition_root
-------------------
t_hash2
(1 row)到此，关于“PostgreSQL12的pg_partition_tree和pg_partition_root系统函数有什么作用”的学习就结束了，希望能够解决大家的疑惑。理论与实践的搭配能更好的帮助大家学习，快去试试吧！若想继续学习更多相关知识，请继续关注亿速云网站，小编会继续努力为大家带来更多实用的文章！
