When we change a parameter, but can't see the effect, there are quite a few possible reasons. Some parameters need a server restart. These are marked in the configuration file as follows:

# (change requires restart)

Then, there are parameters that can be set by a reload of the configuration file after making changes in the file. Reloading the parameters can be done using the following command:

pg_ctl reload

The same can be achieved by executing at psql:

SELECT pg_reload_conf();

We can know whether a server restart is required for a parameter change to take effect by querying pg_settings:

postgres=# SELECT DISTINCT  context FROM pg_settings;
  context   
------------
 backend
 user
 internal
 postmaster
 superuser
 sighup

If the context says postmaster, then a restart of the cluster is required. However, if the context says sighup, pg_ctl a reload will do. For example:

SELECT  name, context FROM  pg_settings WHERE  name 
IN ( 'archive_command','port'); 
      name ...