On 02/21/2017 02:43 PM, Rob Brucks wrote:
That's a great thought!
Comparing between systems (one where I don't issue "notify" and one where I do every minute) yields the same thing: one 8k file named "0000".
If that's truly where notifications are stored, then it looks like I should be good, at least for storage. But I wonder if that file is only used to store notify commands during shutdown/startup?
From the source of async.c:
During start or reboot, clean out the pg_notify directory.
I would guess the 0000 file is like a WAL file it is a pre-initialized
file filled with 0(?)'s
Or if there are any considerations for memory usage…
--Rob
On 2/21/17, 4:38 PM, "Adrian Klaver" <adrian.klaver@xxxxxxxxxxx> wrote:
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@xxxxxxxxx>
> *Date: *Tuesday, February 21, 2017 at 3:38 PM
> *To: *Adrian Klaver <adrian.klaver@xxxxxxxxxxx>
> *Cc: *Rob Brucks <rob.brucks@xxxxxxxxxxxxx>,
> "pgsql-general@xxxxxxxxxxxxxx" <pgsql-general@xxxxxxxxxxxxxx>
> *Subject: *Re: NOTIFY command impact
>
>
>
> On Tue, Feb 21, 2017 at 2:17 PM, Adrian Klaver
> <adrian.klaver@xxxxxxxxxxx <mailto:adrian.klaver@xxxxxxxxxxx>> 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@xxxxxxxxxxx
--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx
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