Re: Question on pgbench output

On Fri, 3 Apr 2009, Tom Lane wrote:

> However, I don't think anyone else has been pgbench'ing transactions
> where client-side libpq has to absorb (and then discard) a megabyte of
> data per xact. I wouldn't be surprised that that eats enough CPU to
> make it an issue. David, did you pay any attention to how busy the
> pgbench process was?

I certainly haven't ever tried that. David, the thing you want to do here
is run "top -c" when pgbench is going. You should see the pgbench process
and a bunch of postmaster ones, with "-c" (or by hitting "c" while top is
running) you can even see what they're all doing. If the pgbench process
is consuming close to 100% of a CPU's time, that means the results it's
giving are not valid--what you're seeing in that case are the limitations
of the testing program instead.

You can even automate collection of that with something like this:

top -b -d 10 -c -n 10000 > top.log &
TOPPID=$!
(run test)
kill $TOPPID

That will save a snapshot every 10 seconds of what's happening during your
test.

--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD