Re: Sending result sets from backend to frontend is _slow_

pgsql-bugs(at)postgresql(dot)org writes:
> When operating over a fast network (ethernet), the sending of select
> result rows from the backend is very slow, ie. it uses only a small
> fraction of available network bandwidth. I am running postgres 7.0.2
> on a Redhat 6.1 install on x86, and using the postodbc driver on
> win2k, and I have looked at the odbc driver code until I am blue in
> the face :-) and I am confident that it is doing the right thing with
> network IO (large read buffers, 4096 bytes by default). There is also
> very low CPU utilization on both machines during large result
> transfers. From this, I believe the problem is in the backend, and I
> think it is probably sending one row per network write.

Certainly not! See the usage of pq_putbytes and pq_flush. The only
not-absolutely-necessary flush in the backend is just after sending
an error or notice message (which one would hope is a noncritical
path). I dunno what is causing your problem, but we're not quite that
dumb ;-)

Depending on what your test query is, it's possible that the server
machine is disk I/O bound --- have you checked?

regards, tom lane