Re: [GENERAL] NOTIFY command impact

On 02/21/2017 02:19 PM, Rob Brucks wrote:
> 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.

Seems the thing to do would be to monitor the size of :

$PG_DATA/pg_notify/

>
>
>
> --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
>
>
>
> On Tue, Feb 21, 2017 at 2:17 PM, Adrian Klaver
> <adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.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.
>
>
>


--
Adrian Klaver
adrian.klaver@aklaver.com