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Since reloading the configuration file is achieved by sending the SIGHUP signal, we can reload the configuration file only for a single backend using the kill command. As you might expect, you may get some strange results from doing this, so don't try it at home.

First, find the PID of the backend using pg_stat_activity. Then, from the OS prompt, issue the following:

kill -SIGHUP   pid

Alternatively, we can do both at once, as shown in this command:

kill -SIGHUP \
&& psql -t -c "select pid from pg_stat_activity limit 1";

This is only useful with a sensible WHERE clause.