I did find a post a while back saying they were discarded, but I wanted to double-check.
I performed some tests to see if listens worked AFTER the notify was issued, they were not. This leads me to believe that the messages are discarded when a listen does not yet exist.
--Rob
From: "David G. Johnston" <david.g.johnston@gmail.com> Date: Tuesday, February 21, 2017 at 3:38 PM To: Adrian Klaver <adrian.klaver@aklaver.com> Cc: Rob Brucks <rob.brucks@rackspace.com>, "pgsql-general@postgresql.org" <pgsql-general@postgresql.org> Subject: Re: [GENERAL] NOTIFY command impact
"There is a queue that holds notifications that have been sent but not yet processed by all listening sessions
Its not clear in the OP that this is the case (it seems to be) but the documentation is non-specific as to what happens when "# of listeners" = 0; I suspect that said messages are created and then immediately discarded - though apparently they do make it over to the standby server too - and likely also immediately discarded there as well.
