Re: TCP network cost

On Thu, Feb 19, 2009 at 02:09:04PM +0100, PFC wrote:
>
> >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...

Here's the core of the problem: I in fact need to transfer exactly that:
a large single field (bytea in my case). I suspect psycopg[12] is having
issues w/ memory allocation, but that's just an unsupported gut feeling.

The final upshot is that I need to restructure my config to use the
large-object API (and hence a snapshot of psycopg2) to get decent
throughput.

> 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.

112 MB/s, and 233 MB/s for localhost. Thanks for the pointer to pv:
looks like a nice tool. Investigating this problem has lead me to a
number of nice 'old school' tools: the other is tcptrace and xplot.org.
I've been hand reading tcpdump output, or clicking around in
ethereal/wireshark. I like tcptrace's approach.

Ross
--
Ross Reedstrom, Ph.D. reedstrm(at)rice(dot)edu
Systems Engineer & Admin, Research Scientist phone: 713-348-6166
The Connexions Project http://cnx.org fax: 713-348-3665
Rice University MS-375, Houston, TX 77005
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