Scott Ribe <scott_ribe@xxxxxxxxxxxxxxxx> writes: >> On Aug 10, 2022, at 3:08 PM, richard coleman <rcoleman.ascentgl@xxxxxxxxx> 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 server was running PostgreSQL, that while there were a number of connections between local 5432 and a random remote port, there was also a connection from a local random port to a remote 5432. If these ports were closed and only 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
