Обсуждение: BUG #17454: Using psql without ipv4 address,the inet_server_port do not return PORT.

The following bug has been logged on the website:

Bug reference:      17454
Logged by:          Laowu wong
Email address:      thbytwo@live.cn
PostgreSQL version: 14.2
Operating system:   centos 7
Description:

It should return the server port when I execute 'select inet_server_port();'
with the command line 'psql -p 15431'.
It seems that if I do not enter the ipv4 address in the
psql-command-line,the pg will return null.

the current behavior:
[postgres@pc67 ~]$ /home/postgres/pgREL1402/bin/psql -p 15431
psql (14.2)
Type "help" for help.

postgres=# select inet_server_port();
 inet_server_port 
------------------

(1 row)

the expected:
[postgres@pc67 ~]$ /home/postgres/pgREL1402/bin/psql -p 15431
psql (14.2)
Type "help" for help.

postgres=# select inet_server_port();
 inet_server_port 
------------------
            15431
(1 row)


the env：
centos 7  x86
PG14.2

The following bug has been logged on the website:

Bug reference:      17454
Logged by:          Laowu wong
Email address:      thbytwo@live.cn
PostgreSQL version: 14.2
Operating system:   centos 7
Description:       

It should return the server port when I execute 'select inet_server_port();'
with the command line 'psql -p 15431'.
It seems that if I do not enter the ipv4 address in the
psql-command-line,the pg will return null.

On Sun, 3 Apr 2022 at 16:50, Wong Simon <thbytwo@live.cn> wrote:
> If I run multiple instances on one server with local socket, how can I distinguish them?I think the port is need.

You distinguish them by the socket NAME whose "extension" is the port
as a decimal string. The socket name is derived from the port option,
but it is not a port. It's clearly specified:

inet_server_addr () → inet
Returns the IP address on which the server accepted the current
connection, or NULL if the current connection is via a Unix-domain
socket.

inet_server_port () → integer
Returns the IP port number on which the server accepted the current
connection, or NULL if the current connection is via a Unix-domain
socket.

I do not know if there is  an "unix_socket_path" option, as there can
be multiple sockets, may be those functions predate
unix_socket_directories being multivalued ( in TCP, with a single
socket listening on 0.0.0.0, you can have connection on different
local address, so it getsockname(2) is needed more ).

But if you just need to distinguish instance on diferent ports, query
the "port" configuration parameter, IIRC this is unique ( although may
be you can somehow reuse it with careful usage of listen_addresses and
unix_socket_directories ).

Francisco Olarte.

On Sun, 3 Apr 2022 at 17:50, David G. Johnston
<david.g.johnston@gmail.com> wrote:
> On Sun, Apr 3, 2022 at 8:36 AM Francisco Olarte <folarte@peoplecall.com> wrote:
>>
>> On Sun, 3 Apr 2022 at 16:50, Wong Simon <thbytwo@live.cn> wrote:
>> > If I run multiple instances on one server with local socket, how can I distinguish them?I think the port is need.
>> You distinguish them by the socket NAME whose "extension" is the port
>> as a decimal string. The socket name is derived from the port option,
>> but it is not a port. It's clearly specified:
> Resorting to string parsing is never desirable, nor is it necessary here.

Socket name seems not to be accessible, as let per a cursory look at
the docs, anyway, but I just looked for unix and for socket in the
index.
And as extension must be port, you are right, no info there.


>> But if you just need to distinguish instance on diferent ports, query
>> the "port" configuration parameter, IIRC this is unique ( although may
>> be you can somehow reuse it with careful usage of listen_addresses and
>> unix_socket_directories ).

> Per the docs It is indeed single-valued.  I don't know what "reuse" would mean in this context but both sockets and
IPhave a specific usage of this setting's value that the DBA cannot alter.
 

Port is single valued, what I meant is I'm not sure if using
socket_dir=/socka, listen_addr=127.0.0.1, data_dir=/dataA and
port=5432 plus socket_dir=/sockb, listen_addr=127.0.0.2,
data_dir=/datab and port=5432 would let you start two correctly
functioning instances in the same machine. In my usage postgres
normally behaves as expected, does not bother doing extra checks, just
listens where it is told to and hums along ( I know of some stupid
programs which, in a situation like this, have code to check if there
is another process listening in the same port, where there is no
transport address collision at all ).

Francisco Olarte.

Francisco Olarte <folarte@peoplecall.com> writes:
>> On Sun, 3 Apr 2022 at 16:50, Wong Simon <thbytwo@live.cn> wrote:
>>> If I run multiple instances on one server with local socket, how can I distinguish them?I think the port is need.

> Port is single valued, what I meant is I'm not sure if using
> socket_dir=/socka, listen_addr=127.0.0.1, data_dir=/dataA and
> port=5432 plus socket_dir=/sockb, listen_addr=127.0.0.2,
> data_dir=/datab and port=5432 would let you start two correctly
> functioning instances in the same machine.

I think relying on port for this purpose is misguided anyway.
We've had requests in the past to let one postmaster listen on
multiple different port numbers; I think the only reason it's
not happened yet is nobody got excited enough to write a patch.

Likewise, inet_server_addr() seems a bit shaky as a server
identity value, since it's already possible to have a postmaster
listening on multiple IP addresses.

If you're trying to identify an installation uniquely, the
machine name and data_directory are probably the best key.
Getting a suitably unique machine name might be tricky.
For localhost connections, though, you could ignore that.

            regards, tom lane