Re: productivity?

Steve Atkins wrote:
> Measuring actual costs (what is the resource cost of session setup and 
> teardown, and of maintaining an open session, for well-implemented, mainstream 
> MTAs?) would seem to be something to do before discussing such a document in 
> much detail.
I've been measuring this for my own product (an SMTP proxy) mostly in 
the course of designing more rigorous test tools. (An unbreakable toy is 
useful for breaking other toys....)
Not surprisingly, at 1 second between messages, the load on my SMTP 
receiver is dramatically lower (and throughput markedly higher) when 
senders hold the connection open; doubly so for TLS, where the 
certificate exchange dominates. Equally unsurprising, when the sender 
holds the connection for 5 minutes and more, I'm having problems with 
hitting my limit on concurrent connections. I'm still looking for where 
the "sweet spot" is between. At present, I blindly 421 any sender that's 
been idle for 3 minutes, but that's little more than a SWAG. I'd really 
like to implement throttling based on a sender's actual load, not just 
on sockets held open; but I don't have the data to cost justify that. Yet.
One issue not raised here: ephemeral port exhaustion. It's a rather 
specialized problem, more of an issue for Windows folks than Linux, and 
mostly an issue for routers, proxies, and similar devices that tend to 
funnel a large volume of mail to smaller number of destinations. But 
it's a real problem, one where reusing existing client connections can 
provide a complete and permanent resolution.
<csg>