PostgreSQL 15：新特性预告

PostgreSQL 15 版本正在开发中，不远的将来就会与大家见面，所以是时候看看未来的一些新功能吧！

1.删除public 模式的创建权限

直到今天，使用 PostgreSQL 14，每个人都可以默认写入public 模式。使用 PostgreSQL 15，这将不再可能。

public 模式现在由“pg_database_owner”拥有。让我们做一个简短的测试。

postgres=# create user PGer;
CREATE ROLE
postgres=# \du
List of roles
Role name | Attributes | Member of
-----------±-----------------------------------------------------------±----------
postgres | Superuser, Create role, Create DB, Replication, Bypass RLS | {}
PGer | | {}

postgres=# \c postgres PGer
You are now connected to database “postgres” as user “PGer”.
postgres=> create table PGCCC (a int);
ERROR: permission denied for schema public
LINE 1: create table PGCCC (a int);
^
postgres=

如果您希望能够再次写入public模式，必须再次明确授予权限。

2.扩展pg_basebackup压缩

pg_basebackup 有一些扩展。特别是压缩得到改善。首先，–compress 现在能够接受一种压缩方法和一个（可选的）压缩级别，例如 gzip:9。

此外 –compress 接受 client-gzip 和 server-gzip 作为压缩方法来定义压缩备份的位置。另一个优点是压缩现在也可以与 –format=p 一起使用。

这使您有机会在服务器端压缩 pg_basebackup 并在客户端自动再次提取它。特别是对于慢速网络连接，这可能是一个好处。

让我们看一下新的 –compress 语法。

postgres@pgdebian:/u99/backup2/ [PG15] pg_basebackup --help | grep -A 1 compress
-z, --gzip compress tar output
-Z, --compress=[{client|server}-]METHOD[:DETAIL]
compress on client or server as specified
-Z, --compress=none do not compress tar output

要创建备份，它现在看起来像这样。非常简单易用。

postgres@pgdebian:/u99/backup2/ [PG15] pg_basebackup -h localhost -p 5438 -Ft --compress=client-gzip:9 --pgdata=/u99/backup2/ -Xs

postgres@pgdebian:/u99/backup2/ [PG15] ll
total 3136
-rw------- 1 postgres postgres 136487 Mar 25 13:40 backup_manifest
-rw------- 1 postgres postgres 3050084 Mar 25 13:40 base.tar.gz
-rw------- 1 postgres postgres 17649 Mar 25 13:40 pg_wal.tar.gz
postgres@pgdebian:/u99/backup2/ [PG15]

或者使用 lz4（可用于客户端或服务器端压缩）：

postgres@pgdebian:/u99/backup2/ [PG15] pg_basebackup -h localhost -p 5438 -Ft --compress=lz4:9 --pgdata=/u99/backup2/ -Xs
postgres@pgdebian:/u99/backup2/ [PG15] ll
total 20096
-rw------- 1 postgres postgres 136487 Mar 25 13:18 backup_manifest
-rw------- 1 postgres postgres 3657232 Mar 25 13:18 base.tar.lz4
-rw------- 1 postgres postgres 16779264 Mar 25 13:18 pg_wal.tar

3.新角色：pg_checkpointer

在 PostgreSQL 14 之前，只允许超级用户执行 CHECKPOINT 命令。从 PostgreSQL 15 开始，有一个名为 pg_checkpointer 的新角色。一旦您将该角色授予用户，它就能够执行 CHECKPOINT 命令。

postgres=# create user PGer;
CREATE ROLE
postgres=# \c postgres PGer
You are now connected to database “postgres” as user “PGer”.
postgres=> checkpoint;
ERROR: must be superuser or have privileges of pg_checkpointer to do CHECKPOINT
postgres=> \c postgres postgres
You are now connected to database “postgres” as user “postgres”.
postgres=# grant pg_checkpointer to PGer;
GRANT ROLE
postgres=# \c postgres PGer
You are now connected to database “postgres” as user “PGer”.
postgres=> checkpoint;
CHECKPOINT
postgres=>

4.合并命令

MERGE 让您有机会在常规表和分区表等中执行一个插入/更新/删除行的 SQL 语句。如果将其用作单个 SQL 命令，则会有一些开销，因为您需要大量的 WHEN / THEN 表达式。

让我们用一个简单的例子来看看这个新特性，两个表相似，但其中一个表还有更多条目。

dvdrental=# select * from PGccc;
category_id | name | last_update
-------------±------------±--------------------
1 | Action | 2006-02-15 09:46:27
2 | Animation | 2006-02-15 09:46:27
3 | Children | 2006-02-15 09:46:27
4 | Classics | 2006-02-15 09:46:27
5 | Comedy | 2006-02-15 09:46:27
6 | Documentary | 2006-02-15 09:46:27
7 | Drama | 2006-02-15 09:46:27
8 | Family | 2006-02-15 09:46:27
9 | Foreign | 2006-02-15 09:46:27
10 | Games | 2006-02-15 09:46:27
11 | Horror | 2006-02-15 09:46:27
12 | Music | 2006-02-15 09:46:27
13 | New | 2006-02-15 09:46:27
14 | Sci-Fi | 2006-02-15 09:46:27
15 | Sports | 2006-02-15 09:46:27
16 | Travel | 2006-02-15 09:46:27
(16 rows)

dvdrental=# select * from PGccc_new;
category_id | name | last_update
-------------±------------±---------------------------
1 | Action | 2006-02-15 09:46:27
2 | Animation | 2006-02-15 09:46:27
3 | Children | 2006-02-15 09:46:27
4 | Classics | 2006-02-15 09:46:27
5 | Comedy | 2006-02-15 09:46:27
6 | Documentary | 2006-02-15 09:46:27
7 | Drama | 2006-02-15 09:46:27
8 | Family | 2006-02-15 09:46:27
9 | Foreign | 2006-02-15 09:46:27
10 | Games | 2006-02-15 09:46:27
11 | Horror | 2006-02-15 09:46:27
12 | Music | 2006-02-15 09:46:27
13 | Biography | 2022-04-12 11:53:34.986878
14 | Sci-Fi | 2006-02-15 09:46:27
15 | Sports | 2006-02-15 09:46:27
16 | Travel | 2006-02-15 09:46:27
17 | Dramedy | 2022-04-12 11:48:49.559058
18 | Love | 2022-04-12 11:49:32.072536
(17 rows)

dvdrental=# MERGE INTO PGccc AS c
USING PGccc_new AS n
ON c.category_id = n.category_id
WHEN MATCHED AND c.name = n.name THEN
DO NOTHING
WHEN MATCHED AND c.name n.name THEN
UPDATE SET name=n.name
WHEN NOT MATCHED THEN
INSERT VALUES (n.category_id, n.name, n.last_update)
;
MERGE 17
dvdrental=#

完成 MERGE 命令后，再次选择原始表，查看它是否按计划添加和更新了所有内容：

dvdrental=# select * from PGccc order by 1;
category_id | name | last_update
-------------±------------±---------------------------
1 | Action | 2006-02-15 09:46:27
2 | Animation | 2006-02-15 09:46:27
3 | Children | 2006-02-15 09:46:27
4 | Classics | 2006-02-15 09:46:27
5 | Comedy | 2006-02-15 09:46:27
6 | Documentary | 2006-02-15 09:46:27
7 | Drama | 2006-02-15 09:46:27
8 | Family | 2006-02-15 09:46:27
9 | Foreign | 2006-02-15 09:46:27
10 | Games | 2006-02-15 09:46:27
11 | Horror | 2006-02-15 09:46:27
12 | Music | 2006-02-15 09:46:27
13 | Biography | 2022-04-12 13:42:26.187381
14 | Sci-Fi | 2006-02-15 09:46:27
15 | Sports | 2006-02-15 09:46:27
16 | Travel | 2006-02-15 09:46:27
17 | Dramedy | 2022-04-12 11:48:49.559058
18 | Love | 2022-04-12 11:49:32.072536
(18 rows)