To reload the configuration files, we send the SIGHUP signal to the postmaster, which then passes that on to all connected backends. That's why some people call reloading the server "sigh-up-ing".
As reloading the configuration file is achieved by sending the SIGHUP signal, we can reload the configuration file just for a single backend using the kill command.
First, find out the pid of the backend using pg_stat_activity. Then, from the OS prompt, issue the following:
kill -SIGHUP pid
I dont understand bold words. Because we have many PIDs for backend and if we kill a PID, how can it get changes from reload configuration file (postgresql.conf)?