Re: NOTIFY command impact

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(dot)g(dot)johnston(at)gmail(dot)com>
Date: Tuesday, February 21, 2017 at 3:38 PM
To: Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com>
Cc: Rob Brucks <rob(dot)brucks(at)rackspace(dot)com>, "pgsql-general(at)postgresql(dot)org" <pgsql-general(at)postgresql(dot)org>
Subject: Re: [GENERAL] NOTIFY command impact

On Tue, Feb 21, 2017 at 2:17 PM, Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com<mailto:adrian(dot)klaver(at)aklaver(dot)com>> wrote:
On 02/21/2017 01:07 PM, Rob Brucks wrote:

Do you see any long-term problems with constantly issuing "NOTIFY"
commands every 30 seconds without an associated "LISTEN" command?

Depending on how long 'long term' is:

https://www.postgresql.org/docs/9.6/static/sql-notify.html

"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.

David J.