Date: Sun, 27 Jan 2013 11:33:28 -0600
From: "ktm@rice.edu" <ktm@rice.edu>
To: belal hamed <belalhamed@gmail.com>
Cc: Richard Neill <rn214@richardneill.org>,
	pgsql-performance@postgresql.org
Subject: Re: PostgreSQL over internet
Message-ID: <20130127173328.GA21220@aart.rice.edu>
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On Sun, Jan 27, 2013 at 03:09:55PM +0300, belal hamed wrote:
> >Here is your "problem". You need to understand the performance
> >characteristics of your communication channel. ADSL is a VERY
> >asymmetric communications channel. Down is usually much faster
> >than up.
> 
> How it could be ADSL problem when it's the same in tow tests ?
> beside data transferred when using tunnel is much bigger (about 10KB)  than
> direct connection (400B)
> so it should be slower when using tunnel but the result shows it was faster
> !!!!
> 

Due to the asymmetric communication, a bigger data output in a single
packet (the result of using compression on the tunnel) will get sent
without waiting. A smaller packet will delay a bit waiting for some
additional data, which in your case does not come. You may want to 
check out this document describing some of what I believe is causing
your observed behavior:

http://www.faqs.org/docs/Linux-HOWTO/ADSL-Bandwidth-Management-HOWTO.html#BACKGROUND

> >When you wrap the communication channel in an IP tunnel, you are
> >collapsing much of the syn-ack of the libpq protocol. You can see
> >the same effect trying to run any sort of X windows application.
> 
> If that so, why these is not same option in Postgresql, Is it necessary to
> use IP tunnel to do that and perform fast fetch?
> 
> 
> >Try creating a simple SSH tunnel
> my server is windows 7
> 
> >It should be possible to distinguish between:
> >  - slowness caused by the database query itself
> >  - slowness caused by the network fundamentally.
> >  - slowness caused by the postgresql/libpq.
> 
> I run the same query on same network connection so I eliminate the
> slowness caused by the database query and network fundamentally,
> nothing left but postgresql/libpq
> 
> not anyone consider there may be a bug when connection to a remote server
> over internet in libpq
> the only different when I used the tunnel is I connect to localhost
> instead  of server IP or domain name (I try both)

You would find that if you log in to your DB server and use libpq
to it over a localhost connection that the performance is good which
points to your network as the problem.

Regards,
Ken


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