feature request: log bytes out for each request

Hi.  Could you please consider logging size of reply, like Apache
httpd does with its logfile?

We've started having intermittent spikes in network usage (the network
interface on the
DB server is getting maxed out) and I suspect there is a single very
large query (just a
working hypothesis at this point).

Logging of answer sizes would help track down an issue like this; plus
you could track
on an ongoing basis how much work you're doing, which may be useful for capacity
planning.

Thanks for a great database server!

Kind regards,
Aleksey