Re: Environment Variable weirdness

[pausmith@nortelnetworks.com (Paul D. Smith)]

%% Salman Ahmed <ssahmed@interlog.com> writes:

  Nathan> It's faster to use a "UNIX domain socket" when all traffic is
  Nathan> local as you avoid some of teh overhead of an IP stack.  Why
  Nathan> waste those milliseconds?

  sa> Would you be willing to explain the technicalities behind that ? Sounds
  sa> like a neat `optimization'. BTW, is this a Debian-specific feature ? I
  sa> haven't seen this in RedHat.

The big advantage of using :0 or unix:0 is that on systems that support
it, it allows the client and server to communicate using _shared memory_
segments.  This is _significantly_ more efficient than having to pass
data buffers through the entire IP stack, even if it doesn't go over the
wire.  Think of the buffer copying being saved...

Look at the output of xdpyinfo and find the extension MIT-SHM... that's
the shared memory extension.  On Linux 2.x, all X servers (that I'm
aware of) support it.

This feature is available to all versions of X11 (on systems that
support it)... that is, it's a feature of X11 in general, and not
specific to XFree86, and certainly not specific to Debian's version of
XFree86.

  sa> Now for a networked system, you'd have to change the DISPLAY env var
  sa> to allow remote X clients to display locally, right ?

On the remote X client, you'd need to use the local hostname in DISPLAY,
yes.

Local clients can still use the efficient :0, of course, regardless of
whether there are remote clients or not.

-- 
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 Paul D. Smith <psmith@baynetworks.com>         Network Management Development
 "Please remain calm...I may be mad, but I am a professional." --Mad Scientist
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   These are my opinions---Nortel Networks takes no responsibility for them.