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Re: TCP network cost

From: PFC <lists(at)peufeu(dot)com>
To: "Ross J(dot) Reedstrom" <reedstrm(at)rice(dot)edu>, pgsql-performance <pgsql-performance(at)postgresql(dot)org>
Subject: Re: TCP network cost
Date: 2009-02-19 13:09:04
Message-ID: op.upln5emacigqcu@soyouz (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
> python w/ psycopg (or psycopg2), which wraps libpq. Same results w/
> either version.

	I've seen psycopg2 saturate a 100 Mbps ethernet connection (direct  
connection with crossover cable) between postgres server and client during  
a benchmark... I had to change the benchmark to not retrieve a large TEXT  
column to remove this bottleneck... this was last year so versions are  
probably different, but I don't think this matters a lot...

> Note the 'bare' transfer times added above. Nothing to write home about
> (~3Mb/sec) but another order of magnitude faster than the postgresql
> transfer.

	You should test with sending a large (>100 MB) amount of data through  
Netcat. This should give you your maximum wire speed. Use /dev/null as the  
test file, and use "pv" (pipe viewer) to measure throughput :

box 1 : pv < /dev/zero | nc -lp 12345
box 2 : nc (ip) 12345 >/dev/null

	On gigabit lan you should get 100 MB/s, on 100BaseT about 10 MB/s. If you  
dont get that, there is a problem somewhere (bad cable, bad NIC, slow  
switch/router, etc). Monitor CPU during this test (vmstat). Usage should  
be low.

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