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PostgreSQL 12 : Streaming Replication
2021/06/25
 
Configure PostgreSQL Streaming Replication.
This configuration is common Primary/Replica settings.
[1]
[2] Configure Primary Host.
[root@www ~]#
vi /var/lib/pgsql/data/postgresql.conf
# line 59 : uncomment and change

listen_addresses = '
*
'
# line 193 : uncomment

wal_level = replica
# line 198 : uncomment

synchronous_commit = on
# line 286 : uncomment (max number of concurrent connections from streaming clients)

max_wal_senders = 10
# line 288 : uncomment and change (minimum number of past log file segments)

wal_keep_segments =
10
# line 300 : uncomment and change

synchronous_standby_names = '
*
'
[root@www ~]#
vi /var/lib/pgsql/data/pg_hba.conf
# end line : comment out existing lines and all new lines

# host replication [replication user] [allowed network] [authentication method]

#host    replication     all             127.0.0.1/32            ident
#host    replication     all             ::1/128                 ident
host    replication     rep_user        10.0.0.30/32            md5
host    replication     rep_user        10.0.0.51/32            md5

# create a user for replication

[root@www ~]#
su - postgres

[postgres@www ~]$
createuser --replication -P rep_user

Enter password for new role:  
# set any password

Enter it again:
[postgres@www ~]$
exit
[root@www ~]#
systemctl restart postgresql
[3] Configure Replica Host.
# stop PostgreSQL and remove existing data

[root@node01 ~]#
systemctl stop postgresql

[root@node01 ~]#
rm -rf /var/lib/pgsql/data/*
# get backup from Primary Host

[root@node01 ~]#
su - postgres

[postgres@node01 ~]$
pg_basebackup -R -h www.srv.world -U rep_user -D /var/lib/pgsql/data -P

Password:  
# password of replication user

30396/30396 kB (100%), 1/1 tablespace
[postgres@node01 ~]$
exit
[root@node01 ~]#
vi /var/lib/pgsql/data/postgresql.conf
# line 59 : uncomment and change

listen_addresses = '
*
'
# line 315 : uncomment

hot_standby = on
[root@node01 ~]#
vi /var/lib/pgsql/data/pg_hba.conf
# end line : comment out existing lines and all new lines

# host replication [replication user] [allowed network] [authentication method]

#host    replication     all             127.0.0.1/32            ident
#host    replication     all             ::1/128                 ident
host    replication     rep_user        10.0.0.30/32            md5
host    replication     rep_user        10.0.0.51/32            md5

[root@node01 ~]#
systemctl start postgresql

[4] If Firewalld is running, allow PostgreSQL service.
[root@www ~]#
firewall-cmd --add-service=postgresql --permanent

success
[root@www ~]#
firewall-cmd --reload

success
[5] That's OK if result of the command below on Primary Host is like follows.
Verify it works normally to create databases or to insert data on Primary Host.
[postgres@www ~]$
psql -c "select usename, application_name, client_addr, state, sync_priority, sync_state from pg_stat_replication;"

 usename  | application_name | client_addr |   state   | sync_priority | sync_state
----------+------------------+-------------+-----------+---------------+------------
 rep_user | walreceiver      | 10.0.0.51   | streaming |             1 | sync
(1 row)
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