Re: Question on pgbench output

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Simon Riggs <simon(at)2ndQuadrant(dot)com>
Cc: David Kerr <dmk(at)mr-paradox(dot)net>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Question on pgbench output
Date: 2009-04-05 15:46:52
Message-ID: 4665.1238946412@sss.pgh.pa.us
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Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
> On Fri, 2009-04-03 at 16:34 -0700, David Kerr wrote:
>> 400 concurrent users doesn't mean that they're pulling 1.5 megs /
>> second every second.

> There's a world of difference between 400 connected and 400 concurrent
> users. You've been testing 400 concurrent users, yet without measuring
> data transfer. The think time will bring the number of users right down
> again, but you really need to include the much higher than normal data
> transfer into your measurements and pgbench won't help there.

Actually pgbench can simulate think time perfectly well: use its \sleep
command in your script. I think you can even set it up to randomize the
sleep time.

I agree that it seems David has been measuring a case far beyond what
his real problem is.

regards, tom lane

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