postgresql主从复制、主从切换

从PostgreSQL 12开始，在执行通过流复制来配置主备数据库的时候，不再需要配置额外配置recovery.conf文件了。取而代之的是在备库环境的$PGDATA路径下配置一个standby.signal文件，注意该文件是1个普通的文本文件，内容为空。理解起来就是，该文件是一个标识文件。如果备库通过执行pg_ctl promote提升为主库的话，那么该文件将自动消失。PostgreSQL 9.

偷懒的小陈

9519人浏览 · 2022-06-24 17:12:55

偷懒的小陈 · 2022-06-24 17:12:55 发布

postgresql主从复制、主从切换

一、不再需要配置recovery.conf文件

二、备库执行基础备份时新的命令行选项-R

PostgreSQL 9.4.10版本：

[postgres@psql ~]$ pg_basebackup -V
pg_basebackup (PostgreSQL) 9.4.10
[postgres@psql ~]$ pg_basebackup --help
pg_basebackup takes a base backup of a running PostgreSQL server.

Usage:
  pg_basebackup [OPTION]...

Options controlling the output:
  -D, --pgdata=DIRECTORY receive base backup into directory
  -F, --format=p|t       output format (plain (default), tar)
  -r, --max-rate=RATE    maximum transfer rate to transfer data directory
                         (in kB/s, or use suffix "k" or "M")
  -R, --write-recovery-conf
                         write recovery.conf after backup
  -T, --tablespace-mapping=OLDDIR=NEWDIR
                         relocate tablespace in OLDDIR to NEWDIR
  -x, --xlog             include required WAL files in backup (fetch mode)
  -X, --xlog-method=fetch|stream
                         include required WAL files with specified method

PostgreSQL 12.8版本：

[postgres@psql ~]$ pg_basebackup -V
pg_basebackup (PostgreSQL) 12.8
[postgres@psql ~]$ pg_basebackup --help
pg_basebackup takes a base backup of a running PostgreSQL server.

Usage:
  pg_basebackup [OPTION]...

Options controlling the output:
  -D, --pgdata=DIRECTORY receive base backup into directory
  -F, --format=p|t       output format (plain (default), tar)
  -r, --max-rate=RATE    maximum transfer rate to transfer data directory
                         (in kB/s, or use suffix "k" or "M")
  -R, --write-recovery-conf
                         write configuration for replication
  -T, --tablespace-mapping=OLDDIR=NEWDIR
                         relocate tablespace in OLDDIR to NEWDIR
      --waldir=WALDIR    location for the write-ahead log directory
  -X, --wal-method=none|fetch|stream
                         include required WAL files with specified method
  -z, --gzip             compress tar output
  -Z, --compress=0-9     compress tar output with given compression level

从对比中，可以看到在9.4.10版本中，-R选项用于创建recovery.conf文件，而在12.8版本中，-R则是用于创建用于replication的配置文件，其实就是生成$PGDATA/standby.signal文件。

三、如何生成standby.signal文件

两种方式，一种是在备库执行基础备份的时候，加上-R选项用于自动创建$PGDATA/standby.signal文件:

[postgres@psql pg12.8]$ pwd
/postgres/pg12.8
[postgres@psql pg12.8]$ ll
total 20
drwxrwxr-x  2 postgres postgres 4096 Oct 19 15:01 bin
drwxrwxr-x  6 postgres postgres 4096 Oct 19 15:01 include
drwxrwxr-x  4 postgres postgres 4096 Oct 19 15:01 lib
drwxrwxr-x  8 postgres postgres 4096 Oct 19 15:01 share
[postgres@psql pg12.8]$ pg_basebackup -h 192.168.40.133 -p 5432 -U replica --password -X stream -Fp --progress -D $PGDATA -R
Password: 
24597/24597 kB (100%), 1/1 tablespace
[postgres@psql pg12.8]$ ll data
total 120
-rw------- 1 postgres postgres   224 Oct 20 15:11 backup_label
drwx------ 5 postgres postgres  4096 Oct 20 15:11 base
drwx------ 2 postgres postgres  4096 Oct 20 15:11 global
drwx------ 2 postgres postgres  4096 Oct 20 15:11 pg_commit_ts
drwx------ 2 postgres postgres  4096 Oct 20 15:11 pg_dynshmem
-rw------- 1 postgres postgres  4867 Oct 20 15:11 pg_hba.conf
-rw------- 1 postgres postgres  1636 Oct 20 15:11 pg_ident.conf
drwx------ 4 postgres postgres  4096 Oct 20 15:11 pg_logical
drwx------ 4 postgres postgres  4096 Oct 20 15:11 pg_multixact
drwx------ 2 postgres postgres  4096 Oct 20 15:11 pg_notify
drwx------ 2 postgres postgres  4096 Oct 20 15:11 pg_replslot
drwx------ 2 postgres postgres  4096 Oct 20 15:11 pg_serial
drwx------ 2 postgres postgres  4096 Oct 20 15:11 pg_snapshots
drwx------ 2 postgres postgres  4096 Oct 20 15:11 pg_stat
drwx------ 2 postgres postgres  4096 Oct 20 15:11 pg_stat_tmp
drwx------ 2 postgres postgres  4096 Oct 20 15:11 pg_subtrans
drwx------ 2 postgres postgres  4096 Oct 20 15:11 pg_tblspc
drwx------ 2 postgres postgres  4096 Oct 20 15:11 pg_twophase
-rw------- 1 postgres postgres     3 Oct 20 15:11 PG_VERSION
drwx------ 3 postgres postgres  4096 Oct 20 15:11 pg_wal
drwx------ 2 postgres postgres  4096 Oct 20 15:11 pg_xact
-rw------- 1 postgres postgres   337 Oct 20 15:11 postgresql.auto.conf
-rw------- 1 postgres postgres 26718 Oct 20 15:11 postgresql.conf
-rw------- 1 postgres postgres     0 Oct 20 15:11 standby.signal
[postgres@psql pg12.8]$

方式2：如果在备库上执行pg_basebackup对主库进行备份的时候，没有使用-R选项的话，我们可以在备库的$PGDATA路径下，touch standby.signal就好了。

记住：该文件只是一个标识文件，它的存在就是告诉数据库，当我们执行pg_ctl start启动的时候，当前库的角色是standby，不是primary角色。

四、部署和配置环境

主机	IP地址	版本
psql-master（主库）	192.168.40.133	psql-14
psql-slave（备库）	192.168.40.147	psql-14

1 修改主机名

[root@localhost ~]# hostnamectl  set-hostname pgsql-master
[root@localhost ~]# bash


[root@localhost ~]# hostnamectl  set-hostname pgsql-slave
[root@localhost ~]# bash

2 配置防火墙规则，放行5432端口

[root@pgsql-master ~]# firewall-cmd --add-port=5432/tcp --permanent
success
[root@pgsql-master ~]# firewall-cmd --reload
success

3 安装postgresql-14

#安装常用工具
[root@pgsql-master ~]# yum -y install vim bash-com*

#创建脚本文件
[root@pgsql-master ~]# touch  install.sh
[root@pgsql-master ~]# chmod +x install.sh 
[root@pgsql-master ~]# cat install.sh 
#!/bin/bash
#配置pgsql网络源
sudo yum install -y https://download.postgresql.org/pub/repos/yum/reporpms/EL-7-x86_64/pgdg-redhat-repo-latest.noarch.rpm
#安装pgsql
sudo yum install -y postgresql14-server
#初始化
sudo /usr/pgsql-14/bin/postgresql-14-setup initdb
#设置开机自启
sudo systemctl enable postgresql-14
sudo systemctl start postgresql-14
#执行脚本
[root@pgsql-master ~]# ./install.sh
#查看服务是否开启
[root@pgsql-master ~]# ss -antl
State      Recv-Q Send-Q   Local Address:Port                  Peer Address:Port              
LISTEN     0      128                  *:22                               *:*                  
LISTEN     0      128          127.0.0.1:5432                             *:*                  
LISTEN     0      100          127.0.0.1:25                               *:*                  
LISTEN     0      128                 :::22                              :::*                  
LISTEN     0      128                ::1:5432                            :::*                  
LISTEN     0      100                ::1:25                              :::*

4 配置环境变量

#切换用户
[root@pgsql-master ~]# su - postgres
上一次登录：三 5月 11 13:57:38 CST 2022pts/0 上
-bash-4.2$ 
#配置环境变量
-bash-4.2$ vi ~/.bash_profile
export PATH=$PATH:$HOME/bin:/usr/pgsql-14/bin   #在最后一行下面添加此行
#添加完后执行：使它立即生效	
-bash-4.2$ source  ~/.bash_profile

5 修改postgres用户密码

[root@pgsql-master ~]# su - postgres
-bash-4.2$ 
-bash-4.2$ psql
psql (14.2)
输入 "help" 来获取帮助信息.

postgres=# 
postgres=# select user;
   user   
----------
 postgres
(1 行记录)

postgres=# 
postgres=# alter role  postgres  with password 'postgres' ;
ALTER ROLE
postgres=# 
postgres=# exit
-bash-4.2$ exit

6 修改数据存放路径（默认的可能在/下，这不太安全）

#建目录/赋权限
mkdir -p /ofa/postgres_data
hown -R postgres:root /ofa/postgres_data
ls -lld /ofa
drwxr-xr-x 3 root root 27 Dec  1 12:28 /ofa
ls -lld /ofa/postgres_data
drwxr-xr-x 2 postgres root 6 Dec  1 12:28 /ofa/postgres_data

vi  /var/lib/pgsql/14/data/postgresql.conf
data_directory='/ofa/postgres_data'
#同步数据
rsync -av /var/lib/pgsql/14/data/ /ofa/postgres_data/

#重启数据库
systemctl restart postgresql-14

也可以使用默认数据存放路径：/var/lib/pgsql/14/data/

五、执行stream主备配置流程

主体思路跟PostgreSQL 11及以前版本的配置流程大同小异，甚至是更简单一些了。

1 主库切换用户，修改监听地址

[root@pgsql-master ~]# su - postgres
上一次登录：一 5月  9 10:48:28 CST 2022pts/0 上
-bash-4.2$ 

#修改监听地址
-bash-4.2$ psql -c "ALTER SYSTEM SET listen_addresses TO '*';"
用户 postgres 的口令：
ALTER SYSTEM
-bash-4.2$ 

#改配置文件
-bash-4.2$ vim /var/lib/pgsql/14/data/postgresql.conf
...
#listen_addresses = 'localhost'         # what IP address(es) to listen on;
listen_addresses = '*'
...

2 主库创建流复制的用户

方式一：
-bash-4.2$  psql -c "CREATE ROLE replicator login replication encrypted password 'postgres';"
用户 postgres 的口令：
CREATE ROLE
-bash-4.2$ 

方式二：
-bash-4.2$ createuser --replication -P -e replicator
为新角色输入的口令: 
再输入一遍: 
口令: 
SELECT pg_catalog.set_config('search_path', '', false);
CREATE ROLE replicator PASSWORD 'SCRAM-SHA-256$4096:gY5s1JPnO4nueRyTiEcHEQ==$C9KLSfPPrX/9XQ9kdzzhY65E01B4AaS9g5WbEl1Bl50=:qiMzW4B+9kaZxXhfQlxu73mwf3S9TORjOBC9RWVaR9c=' NOSUPERUSER NOCREATEDB NOCREATEROLE INHERIT LOGIN REPLICATION;
-bash-4.2$

3 主库修改pg_hba.conf文件，允许备库IP通过复制用户访问数据库

-bash-4.2$ vim /var/lib/pgsql/14/data/pg_hba.conf
...
#在最下面添加
host    replication    replicator     192.168.40.147/24         md5
...

最后一行，添加了replicaor用户可以从备库IP 192.168.40.147访问主库。

4 备库备份旧数据，删掉，然后备份主库数据

-bash-4.2$ mkdir  /opt/psql_data
-bash-4.2$ cp -R /var/lib/pgsql/14/data/ /opt/psql_data
-bash-4.2$ cd /var/lib/pgsql/14/data/ 
-bash-4.2$ rm -rf *

5 备库上执行对于主库的基础备份

-bash-4.2$ pg_basebackup -h 192.168.40.133 -D /var/lib/pgsql/14/data -U replicator -P -v -R -X stream -C -S pgstandby1
口令: 
pg_basebackup: 开始基础备份，等待检查点完成
pg_basebackup: 已完成检查点
pg_basebackup: 预写日志起始于时间点: 0/2000028, 基于时间轴1
pg_basebackup: 启动后台 WAL 接收进程
pg_basebackup: 已创建复制槽"pgstandby1"
26952/26952 kB (100%), 1/1 表空间                                         
pg_basebackup: 预写日志结束点: 0/2000100
pg_basebackup: 等待后台进程结束流操作...
pg_basebackup: 同步数据到磁盘...
pg_basebackup: 将backup_manifest.tmp重命名为backup_manifest
pg_basebackup: 基础备份已完成

注意，备份选项上带有-R选项。

4 备库就可以执行pg_ctl start启动了

这时，就可以看到备库服务器上自动生成了standby.signal文件。同时，也看到在$PGDATA路径下，数据库自动帮我们配置了关于流复制的主库的信息：

-bash-4.2$ cat data/postgresql.auto.conf
# Do not edit this file manually!
# It will be overwritten by the ALTER SYSTEM command.
primary_conninfo = 'user=replicator password=postgres host=192.168.40.133 port=5432 sslmode=disable sslcompression=0 gssencmode=disable krbsrvname=postgres target_session_attrs=any'

当然了，如果我们没有使用-R来备份主库的话。我们完全可以在备库上手工创建standby.signal文件，然后手工编辑postgresql.auto.conf，并在其内容中配置主库的信息。

5 备库数据库进程信息

-bash-4.2$  ps -ef|grep postgres
postgres  8911     1  0 Oct20 ?        00:00:00 /postgres/pg12.8/bin/postgres
postgres  8912  8911  0 Oct20 ?        00:00:00 postgres: startup   recovering 000000010000000000000003
postgres  8913  8911  0 Oct20 ?        00:00:00 postgres: checkpointer   
postgres  8914  8911  0 Oct20 ?        00:00:00 postgres: background writer  
postgres  8915  8911  0 Oct20 ?        00:00:00 postgres: stats collector   
postgres  8916  8911  0 Oct20 ?        00:00:32 postgres: walreceiver   streaming 0/3000148
root     18015 18014  0 16:13 pts/0    00:00:00 su - postgres
postgres 18016 18015  0 16:13 pts/0    00:00:00 -bash
postgres 18055 18016  0 16:13 pts/0    00:00:00 ps -ef
postgres 18056 18016  0 16:13 pts/0    00:00:00 grep --color=auto postgres

备库上，可以看到walreceiver进程，正在读取日志streaming 0/3000148，执行恢复recovering 000000010000000000000003。

6 主库数据库进程信息

-bash-4.2$  ps -ef|grep postgres
postgres  3708     1  0 Oct20 ?        00:00:00 /postgres/pg12.8/bin/postgres
postgres  3710  3708  0 Oct20 ?        00:00:00 postgres: checkpointer   
postgres  3711  3708  0 Oct20 ?        00:00:00 postgres: background writer  
postgres  3712  3708  0 Oct20 ?        00:00:00 postgres: walwriter   
postgres  3713  3708  0 Oct20 ?        00:00:00 postgres: autovacuum launcher  
postgres  3714  3708  0 Oct20 ?        00:00:00 postgres: stats collector   
postgres  3715  3708  0 Oct20 ?        00:00:00 postgres: logical replication launcher  
postgres  4174  3708  0 Oct20 ?        00:00:00 postgres: walsender replicator 192.168.40.147(57926) streaming 0/3000148
root     30410 30409  0 16:11 pts/1    00:00:00 su - postgres
postgres 30411 30410  0 16:11 pts/1    00:00:00 -bash
postgres 30868 30411  0 16:13 pts/1    00:00:00 ps -ef
postgres 30869 30411  0 16:13 pts/1    00:00:00 grep --color=auto postgres

主库上看到，后台进程walsender，正在向replicator 192.168.40.147(57926) streaming 0/3000148推送日志信息。

7 主库查看数据库复制信息

-bash-4.2$  psql -xc "select * from pg_stat_replication"
-[ RECORD 1 ]----+------------------------------
pid              | 4174
usesysid         | 16384
usename          | replicator
application_name | walreceiver
client_addr      | 192.168.40.147
client_hostname  | 
client_port      | 57926
backend_start    | 2021-10-20 15:45:37.817863+08
backend_xmin     | 
state            | streaming
sent_lsn         | 0/3000148
write_lsn        | 0/3000148
flush_lsn        | 0/3000148
replay_lsn       | 0/3000148
write_lag        | 
flush_lag        | 
replay_lag       | 
sync_priority    | 0
sync_state       | async
reply_time       | 2021-10-21 16:11:58.438541+08

六、主备切换及注意事项

如果因为意外或故障导致主库不可用的情况下，可以直接将备库提升为主库对外提供服务。然后视具体情况看原来的主库是否需要重建，或者是否待故障恢复之后，可以直接作为新的备库，然后从新的主库(原备库)同步数据。

下面是模拟切换步骤：

1 主库停止，模拟故障

-bash-4.2$  ps -ef|grep postgres
postgres  3708     1  0 Oct20 ?        00:00:00 /postgres/pg12.8/bin/postgres
postgres  3710  3708  0 Oct20 ?        00:00:00 postgres: checkpointer   
postgres  3711  3708  0 Oct20 ?        00:00:00 postgres: background writer  
postgres  3712  3708  0 Oct20 ?        00:00:00 postgres: walwriter   
postgres  3713  3708  0 Oct20 ?        00:00:00 postgres: autovacuum launcher  
postgres  3714  3708  0 Oct20 ?        00:00:00 postgres: stats collector   
postgres  3715  3708  0 Oct20 ?        00:00:00 postgres: logical replication launcher  
postgres  4174  3708  0 Oct20 ?        00:00:00 postgres: walsender replicator 192.168.40.147(57926) streaming 0/3000148
postgres  4747 30411  0 16:42 pts/1    00:00:00 ps -ef
postgres  4748 30411  0 16:42 pts/1    00:00:00 grep --color=auto postgres
root     30410 30409  0 16:11 pts/1    00:00:00 su - postgres
postgres 30411 30410  0 16:11 pts/1    00:00:00 -bash

-bash-4.2$  pg_ctl status
pg_ctl: server is running (PID: 3708)
/postgres/pg12.8/bin/postgres

-bash-4.2$  pg_ctl stop -m fast
waiting for server to shut down.... done
server stopped

-bash-4.2$  ps -ef|grep postgres
postgres  4843 30411  0 16:43 pts/1    00:00:00 ps -ef
postgres  4844 30411  0 16:43 pts/1    00:00:00 grep --color=auto postgres
root     30410 30409  0 16:11 pts/1    00:00:00 su - postgres
postgres 30411 30410  0 16:11 pts/1    00:00:00 -bash

-bash-4.2$  pg_ctl status
pg_ctl: no server running

通过pg_ctl stop -m fast停止原来的主库之后，数据库后台进程都没有了。

2 备库提升为新主库，对外提供服务

-bash-4.2$  ps -ef|grep postgres
postgres  8911     1  0 Oct20 ?        00:00:00 /postgres/pg12.8/bin/postgres
postgres  8912  8911  0 Oct20 ?        00:00:00 postgres: startup   recovering 000000010000000000000003
postgres  8913  8911  0 Oct20 ?        00:00:00 postgres: checkpointer   
postgres  8914  8911  0 Oct20 ?        00:00:00 postgres: background writer  
postgres  8915  8911  0 Oct20 ?        00:00:00 postgres: stats collector   
root     18015 18014  0 16:13 pts/0    00:00:00 su - postgres
postgres 18016 18015  0 16:13 pts/0    00:00:00 -bash
postgres 25404 18016  0 16:43 pts/0    00:00:00 ps -ef
postgres 25405 18016  0 16:43 pts/0    00:00:00 grep --color=auto postgres
-bash-4.2$  pg_ctl status
pg_ctl: server is running (PID: 8911)
/postgres/pg12.8/bin/postgres
-bash-4.2$  pg_ctl promote
waiting for server to promote.... done
server promoted
-bash-4.2$  ps -ef|grep postgres
postgres  8911     1  0 Oct20 ?        00:00:00 /postgres/pg12.8/bin/postgres
postgres  8913  8911  0 Oct20 ?        00:00:00 postgres: checkpointer   
postgres  8914  8911  0 Oct20 ?        00:00:00 postgres: background writer  
postgres  8915  8911  0 Oct20 ?        00:00:00 postgres: stats collector   
root     18015 18014  0 16:13 pts/0    00:00:00 su - postgres
postgres 18016 18015  0 16:13 pts/0    00:00:00 -bash
postgres 25622  8911  0 16:44 ?        00:00:00 postgres: walwriter   
postgres 25623  8911  0 16:44 ?        00:00:00 postgres: autovacuum launcher  
postgres 25624  8911  0 16:44 ?        00:00:00 postgres: logical replication launcher  
postgres 25628 18016  0 16:44 pts/0    00:00:00 ps -ef
postgres 25629 18016  0 16:44 pts/0    00:00:00 grep --color=auto postgres
-bash-4.2$

重要1：启动备库为新主库的命令是pg_ctl promote。

提升备库为主库之后，可以看到，后台进程中不再有startup recovering，以及walreceiver streaming进程了。同时，多了postgres: walwriter 写进程。

重要2：$PGDATA/standby.signal文件自动消失了。这是告诉PostgreSQL，我现在不再是备库了，我的身份是主库了。

3 新主库修改pg_hba.conf文件

修改新主库(原备库192.168.40.147)的$PGDATA/pg_hba.conf文件，在其中添加允许新备库(原主库192.168.40.133)可以通过replica用户访问数据库的条目信息。

host    replication     replicaotr             192.168.40.133/24           md5

如果不做这一步配置的话，将来启动原主库为新备库的时候，可能会遇到下述错误。

2021-10-21 17:13:20.464 CST [11394] FATAL:  could not connect to the primary server: FATAL:  no pg_hba.conf entry for replication connection from host "192.168.40.133", user "replica", SSL off
2021-10-21 17:13:20.466 CST [11395] FATAL:  could not connect to the primary server: FATAL:  no pg_hba.conf entry for replication connection from host "192.168.40.133", user "replica", SSL off

注意：如果主从环境的数据库没有配置浮动IP的话，则这里的IP地址，应该直接填原主库的实际IP地址。

4 原主库新建$PGDATA/standby.signal文件

-bash-4.2$  pwd
/var/lib/pgsql/14/data
-bash-4.2$  touch standby.signal

-bash-4.2$  ll standby.signal 
-rw-rw-r-- 1 postgres postgres 0 Oct 21 16:54 standby.signal

注意：这一步骤非常非常重要，如果不配置该文件的话，那么原来的主库一旦重新启动话，就将成为了1个新的独立主库，脱离了主从数据库环境。

5 原主库修改$PGDATA/postgresql.auto.conf文件

注意，应该用单引号，而不是双引号。否则遇到下述错误。

-bash-4.2$  cat postgresql.auto.conf 
# Do not edit this file manually!
# It will be overwritten by the ALTER SYSTEM command.
primary_conninfo="user=replica password=replica host=192.168.40.147 port=5432"
-bash-4.2$  
-bash-4.2$  pg_ctl start -l ~/pg.log 
waiting for server to start.... stopped waiting
pg_ctl: could not start server
Examine the log output.
-bash-4.2$  tailf ~/pg.log
数据库启动日志
2021-10-21 09:07:06.512 GMT [10045] LOG:  syntax error in file "/postgres/pg12.8/data/postgresql.auto.conf" line 3, near token """
2021-10-21 09:07:06.512 GMT [10045] FATAL:  configuration file "postgresql.auto.conf" contains errors

修改$PGDATA/postgresql.auto.conf配置文件为下述正确的格式：

-bash-4.2$  cat postgresql.auto.conf 
# Do not edit this file manually!
# It will be overwritten by the ALTER SYSTEM command.
primary_conninfo='user=replica password=replica host=192.168.40.147 port=5432'

6 启动原主库，变为新备库

-bash-4.2$  pg_ctl start -l ~/pg.log 
waiting for server to start.... done
server started
-bash-4.2$  ps -ef|grep postgres
root      8116  8115  0 16:58 pts/0    00:00:00 su - postgres
postgres  8118  8116  0 16:58 pts/0    00:00:00 -bash
root      8598  8597  0 17:00 pts/2    00:00:00 su - postgres
postgres  8600  8598  0 17:00 pts/2    00:00:00 -bash
postgres 11368  8118  0 17:13 pts/0    00:00:00 tailf pg.log
postgres 11389     1  0 17:13 ?        00:00:00 /postgres/pg12.8/bin/postgres
postgres 11390 11389  0 17:13 ?        00:00:00 postgres: startup   recovering 000000020000000000000003
postgres 11391 11389  0 17:13 ?        00:00:00 postgres: checkpointer   
postgres 11392 11389  0 17:13 ?        00:00:00 postgres: background writer  
postgres 11393 11389  0 17:13 ?        00:00:00 postgres: stats collector   
postgres 11440 11389  0 17:13 ?        00:00:00 postgres: walreceiver   streaming 0/3013AC8
postgres 12545 30411  0 17:18 pts/1    00:00:00 ps -ef
postgres 12546 30411  0 17:18 pts/1    00:00:00 grep --color=auto postgres
root     30410 30409  0 16:11 pts/1    00:00:00 su - postgres
postgres 30411 30410  0 16:11 pts/1    00:00:00 -bash
-bash-4.2$  tailf pg.log 
2021-10-21 17:13:45.488 CST [11440] LOG:  fetching timeline history file for timeline 2 from primary server
2021-10-21 17:13:45.493 CST [11440] LOG:  started streaming WAL from primary at 0/3000000 on timeline 1
2021-10-21 17:13:45.493 CST [11440] LOG:  replication terminated by primary server
2021-10-21 17:13:45.493 CST [11440] DETAIL:  End of WAL reached on timeline 1 at 0/30001C0.
2021-10-21 17:13:45.494 CST [11390] LOG:  new target timeline is 2
2021-10-21 17:13:45.494 CST [11440] LOG:  restarted WAL streaming at 0/3000000 on timeline 2
2021-10-21 17:13:45.539 CST [11390] LOG:  redo starts at 0/30001C0

这样，就完成了一次主从数据库环境的切换操作了。