On Aug 16, 2014, at 9:01 AM, Nick Guenther <nguen...@uwaterloo.ca> wrote:

> 
> 
> On August 16, 2014 11:41:02 AM EDT, lin <jlu...@163.com> wrote:
>> Hi all,
>> I change the value of "unix_socket_directories" in postgresql.conf , 
>> then restart the database, but it cannot connect the database used like
>> this 
>> "psql -d postgres -p 5432" ,  it must given the parameter " -h /xx/xx"
>> to use the Unix domain socket。
>>   how to fix   this issue ?
> 
> I'll start by saying that your test case is very clear, and thank you for it. 
> I am unsure what your goal is, however. I assume you are trying to set up 
> parallel postgres processes, for debugging. I've done this recently, for that 
> reason.
> 
> First thing to point out is that you need only one of -h and -p.  They are 
> redundant options, because you only connect to postgres either over TCP (-p) 
> or with a unix domain socket (-h).

Not really. In the case of a TCP connection you need -h for the hostname and -p 
for the port. For a unix socket connection you use -h to specify the directory 
the unix socket is in, and -p is used to generate the name of the socket within 
that directory. If you omit one or both then the compiled-in defaults will be 
used, but it still uses both values to connect.

> 
> Second, what you're seeing is necessary. If you change the default, then psql 
> doesn't know where to look. However, you can recover the old behaviour with 
> shell tricks:
> $ alias psql='psql -h /xx/xx'
> $ psql -d postgres

Setting environment variables to point to your preferred instance will also 
work - and it'll work with any client that uses libpq (which is probably almost 
everything that's not java).

Cheers,
  Steve

> 
> (Personally, I wrote a short wrapper script called "client.sh" which 
> depth-first searches for a postgres db directory and the runs 'psql -h' with 
> the first one it finds; equally well you could have this script install an 
> alias)
> 
> Are you perhaps confused about what a unix domain socket is? Why are you 
> changing it? This is a decent description of it: 
> http://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man4/unix.4
> 
> 
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