Re: [GENERAL] NOTIFY command impact
От | Adrian Klaver |
---|---|
Тема | Re: [GENERAL] NOTIFY command impact |
Дата | |
Msg-id | c3a2f451-2750-ce62-1bd5-5c5603db9c9f@aklaver.com обсуждение исходный текст |
Ответ на | Re: [GENERAL] NOTIFY command impact (Rob Brucks <rob.brucks@rackspace.com>) |
Список | pgsql-general |
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: one8k 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 wonderif 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@aklaver.com> 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@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 > > -- Adrian Klaver adrian.klaver@aklaver.com
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