I just upgraded my MacMini Server from Lion Server to Mountain Lion using OS X Server. I am having the same problem with PostgreSQL that I did last year when I first instal
apt-get install postgres-xc-client
apt-get install postgres-xc
Open 'postgresql.conf' in you favourite editor. Look for the variable 'unix_socket_directories', it will most likely look like this:
unix_socket_directories = '/private/tmp/'
Change the line to this:
unix_socket_directories = '/var/pgsql_socket/'
Note if you want the socket files in more than one directory comma separate them.