From: Tom Lane <tgl@sss.pgh.pa.us>
To: Scott Ribe <scott_ribe@elevated-dev.com>
cc: richard coleman <rcoleman.ascentgl@gmail.com>, pgsql-admin@postgresql.org
Subject: Re: postgresql definitive list of network resources used/needed?
In-reply-to: <200DE464-2992-4D0C-96F1-6656E1CE932A@elevated-dev.com>
References: 
 <CAGA3vBstbWk88KvfJD0WzR89omKy9v+P_Z-S4p=_HC0g-xR58w@mail.gmail.com>
 <200DE464-2992-4D0C-96F1-6656E1CE932A@elevated-dev.com>
Comments: In-reply-to Scott Ribe <scott_ribe@elevated-dev.com>
	message dated "Wed, 10 Aug 2022 15:24:38 -0600"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <384609.1660168232.1@sss.pgh.pa.us>
Content-Transfer-Encoding: quoted-printable
Date: Wed, 10 Aug 2022 17:50:32 -0400
Message-ID: <384610.1660168232@sss.pgh.pa.us>
Archived-At: 
 <https://www.postgresql.org/message-id/384610.1660168232%40sss.pgh.pa.us>
Precedence: bulk

Scott Ribe <scott_ribe@elevated-dev.com> writes:
>> On Aug 10, 2022, at 3:08 PM, richard coleman <rcoleman.ascentgl@gmail.c=
om> wrote:
>> Apparently, I've discovered that PostgreSQL connects to itself over UDP=
.  =


> No it doesn't. (It can use Unix domain sockets for local connections.)

Possibly Richard is seeing the stats collector pipe, which is TCP local
loopback on a random port number.  (That'll be gone in v15, but it
exists in all current releases.)

> I've also discovered, while looking at the network while one of our serv=
er was running PostgreSQL, that while there were a number of connections b=
etween local 5432 and a random remote port, there was also a connection fr=
om a local random port to a remote 5432.  If these ports were closed and o=
nly 5432 left open, this connection would have failed.

postgres_fdw outgoing connection to a remote server?  Maybe it's something
else, but that's the most obvious theory.

The incoming-connection port and the stats loopback are the only
IP connections in a bare-bones Postgres system, but I think few
people run it completely bare-bones.  There's no such thing as
a "definitive list" of ports used as long as you've told us
nothing about (for example) your backup or replication setup,
not to mention postgres_fdw and other extensions you might use.

			regards, tom lane