Executing inet_server_addr/port() in parallel workers

Hi,

While investigating a customer issue it's turned out that if a
parallel worker executes inet_server_addr() and inet_server_port() the
results are always null because MyProcPort is not set in parallel
workers. We can reproduce it in all supported versions higher than
9.6. Here is an example:

postgres=# select inet_server_addr(), inet_server_port();
inet_server_addr | inet_server_port
------------------+------------------
172.254.99.88 | 5432
(1 row)

postgres=# select inet_client_addr(), inet_client_port();
inet_client_addr | inet_client_port
------------------+------------------
172.254.99.109 | 31383
(1 row)

postgres=# set force_parallel_mode to on;
SET
postgres=# select inet_server_addr(), inet_server_port();
inet_server_addr | inet_server_port
------------------+------------------
|
(1 row)

postgres=# select inet_client_addr(), inet_client_port();
inet_client_addr | inet_client_port
------------------+------------------
172.254.99.109 | 31383
(1 row)

To fix this issue, I think there are two options:

1. Inherits the local address information from postmaster or the
leader to parallel workers.
2. Have both inet_server_addr() and inet_server_port() parallel restricted.

Since auxiliary processes including parallel workers don't communicate
directly to the client, this information is basically not necessary.
Also, the option #1 needs code change to pass the information, which
brings complexity and is not good in terms of back-patching. So I'd
prefer the option #2. I've attached the patch doing the option #2.

Regards,

--
Masahiko Sawada
EnterpriseDB: https://www.enterprisedb.com/