PostgreSQL version:


By default, connection log messages only show the IP address of the connecting host. Turning this parameter on causes logging of the host name as well. Note that depending on your host name resolution setup this might impose a non-negligible performance penalty. This parameter can only be set in the postgresql.conf file or on the server command line.


As this setting requires resolution of each connecting hostname, it's pretty much always too expensive to have on, even when troubleshooting.