step by step to change replication status (sync or async) in postgresql database

If you don't want transactions to wait until a synchronous replica acknowledges a commit,
then you don't want synchronous replication. You want async replication and should simply
remove the synchronous_standby_names

Step 1: Check sync status in Primary Database

[root@pg_primary ~]# su - postgres
Last login: Sun Dec 10 22:45:00 EST 2017 on pts/0
-bash-4.2$ psql -c "select application_name, state, sync_priority, sync_state from pg_stat_replication;"
 application_name |   state   | sync_priority | sync_state
------------------+-----------+---------------+------------
 walreceiver      | streaming |             1 | sync
(1 row)

-bash-4.2$ psql -c "select application_name, state, sync_priority, sync_state from pg_stat_replication;"
 application_name |   state   | sync_priority | sync_state
------------------+-----------+---------------+------------
 walreceiver      | streaming |             1 | sync
(1 row)

Step 2: Modify the postgresql.conf file of Primary Database

-bash-4.2$
-bash-4.2$ vim /var/lib/pgsql/9.5/data/postgresql.conf
#synchronous_standby_names = '' # standby servers that provide sync rep
#synchronous_standby_names = 'pgslave001'
synchronous_standby_names = 'walreceiver'

--Comment the Values synchronous_standby_names--
#synchronous_standby_names = 'walreceiver'

Step 3: Restart the postgresql service

[root@pg_primary ~]# systemctl stop postgresql-9.5.service
[root@pg_primary ~]# systemctl start postgresql-9.5.service


Step 4: Check Database Sync Status

[root@pg_primary ~]# su - postgres
Last login: Mon Dec 11 05:35:05 EST 2017 on pts/0
-bash-4.2$ psql -c "select application_name, state, sync_priority, sync_state from pg_stat_replication;"
 application_name |   state   | sync_priority | sync_state
------------------+-----------+---------------+------------
 walreceiver      | streaming |             0 | async
(1 row)

-bash-4.2$ psql -x -c "select * from pg_stat_replication;"
-[ RECORD 1 ]----+-----------------------------
pid              | 5923
usesysid         | 16393
usename          | repuser
application_name | walreceiver
client_addr      | 192.168.159.135
client_hostname  |
client_port      | 39369
backend_start    | 2017-12-11 05:39:48.74948-05
backend_xmin     |
state            | streaming
sent_location    | 0/3E0000D0
write_location   | 0/3E0000D0
flush_location   | 0/3E0000D0
replay_location  | 0/3E0000D0
sync_priority    | 0
sync_state       | async

-bash-4.2$

----Check With data Primary and Standby--------
----In Primary------
[root@pg_primary ~]# su - postgres
Last login: Mon Dec 11 05:35:05 EST 2017 on pts/0
-bash-4.2$ psql
psql (9.5.10)
Type "help" for help.

postgres=# insert into sebl values('NRB Bank Ltd','Gulshan');
INSERT 0 1
postgres=#

-----In Standby------
[root@pg_standby data]# su - postgres
Last login: Mon Dec 11 05:34:07 EST 2017 on pts/1
-bash-4.2$ psql
psql (9.5.10)
Type "help" for help.

postgres=# select * from sebl;
      org_name       |    address   
---------------------+---------------
 Southeast Bank Ltd. | Eunoos Center
 Estern Bank Ltd.    | Gulshan
 Bangladesh Bank     | Motijill
 Prime Bank Ltd      | Motijill
 City Bank Ltd       | Gulshan
 Brac Bank Ltd       | Gulshan
 Exim Bank Ltd       | Gulshan
 MTBL Bank Ltd       | Gulshan
 Meghna Bank Ltd     | Gulshan
 Uttara Bank Ltd     | Motijill
 UCB Bank Ltd        | Gulshan
 NRB Bank Ltd        | Gulshan
(12 rows)

postgres=#