Re: Receive buffer size for the statistics socket

I wrote:
> I propose that it'd be a good idea to try to set the stats socket's
> receive buffer size to be a minimum of, say, 100K on all platforms.
> Code for this would be analogous to what we already have in pqcomm.c
> (circa line 760) for forcing up the send buffer size, but SO_RCVBUF
> not SO_SNDBUF.

I experimented with the attached patch. Modern platforms such as
recent Linux and macOS seem to have default receive buffer sizes
in the 100K-200K range. The default is less in older systems, but
even my very oldest dinosaurs will let you set it to at least 256K.
(Don't have Windows to try, though.)

I propose committing this (less the debug logging part) to HEAD
once the beta is out, and then back-patching if it doesn't break
anything and seems to improve matters on frogmouth.

regards, tom lane