From: Tom Lane <tgl@sss.pgh.pa.us>
To: Mariel Cherkassky <mariel.cherkassky@gmail.com>
cc: pgsql-performance@lists.postgresql.org
Subject: Re: postgresql unix socket connections
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Comments: In-reply-to Mariel Cherkassky <mariel.cherkassky@gmail.com>
	message dated "Wed, 09 Jan 2019 10:35:41 +0200"
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Date: Wed, 09 Jan 2019 09:55:02 -0500
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Mariel Cherkassky <mariel.cherkassky@gmail.com> writes:
> I'm trying to understand some issues that I'm having with the unix_socket
> settings and pgsql.
> I have 2 machines with pg v9.2.5 with the same next settings :
> #listen_addresses = 'localhost'
> #unix_socket_directory = ''

This will result in the server creating the socket in whatever it thinks
is the default socket directory.  Traditionally PG uses /tmp as the
default socket directory, and your netstat result is consistent with that:

> unix  2      [ ACC ]     STREAM     LISTENING     51587140 3729/postgres
>    /tmp/.s.PGSQL.5432

However, this:

> psql: could not connect to server: No such file or directory
>         Is the server running locally and accepting
>         connections on Unix domain socket
> "/var/run/postgresql/.s.PGSQL.5432"?

shows that your psql is using a libpq that thinks the default socket
directory is /var/run/postgresql.  That's a build-time option, and
I recall that Red Hat builds their postgresql package that way.
I'm not 100% sure which way the PGDG RPMs do it.

You could override libpq's default, for instance via "psql -h /tmp".
But probably you'd be better off removing any packages that provide
libpq versions that don't match your server.

Alternatively, you could configure the server to create socket
files in both places.

			regards, tom lane