Timeout parameters

Hi, all.

I'd like to suggest introducing two parameters to handle client-server communication timeouts.
That is "tcp_user_timeout" and "socket_timeout" parameter.

I implemented "tcp_user_timeout" parameter
in both backend and frontend side.
This parameter enables us to
use TCP_USER_TIMEOUT option on linux.
If the parameter is specified, the process sets the value to
TCP_USER_TIMEOUT option.
In my opinion, this option is needed for the following situation:
If the server can't return an ack packet to the request from the client,
the client performs retransmission processing.
In this case TCP keepalive option can't work.
Therefore we need TCP USER TIMEOUT option.
Andrei Yahorau also refer to the necessity of this option in [1].

"socket_timeout" is the application layer timeout parameter
from when frontend issues SQL query
to when frontend receives the execution result from backend.
When this parameter is active and timeout occurs,
frontend close the socket.
It is a merit for client to set the maximum time
to wait for SQL.

I'm waiting for your opinions or reviews.

[1] https://www.postgresql.org/message-id/flat/OF4C8A68CE.A350F319-ON432582D0.0028A5FF-432582D0.002FEE28%40iba.by

Bes regards,
---------------------
Ryohei Nagaura