Victor Duchovni:
> > SwiftMail is submitting via SMTP.
>
> It sure looks like the SwiftMail engine is either not very swift, or
> is configured well below peak throughput. Postfix is input-starved,
> not output saturated. Does SwiftMail implement SMTP PIPELINING, do
> you have verbose logging enabled slowing down message input?
>
> > As far as parallel submissions, we're only doing three at a time
> > (three SwiftMail processes sending at a time). Our in_flow_delay
> > parameter is set to 0.
>
> This is almost certainly way too low. To get peak utilization your
> input concurrency should be in the 10-20 range, assuming that no
> silly latency incurred in slow DNS resolution of the PTR and A
> records of the connecting client.
>
> You need to look at the delay=a/b/c/d numbers of non-fallback mail and
> determine the typical value of "a", this will give you the input engine
> latency. To get throughput increase concurrency while making sure that
> the output is keeping up and input latency is not spiking.
I agree with this assessment. Your mail sending process is CPU
limited; it appears to saturate one of your two CPU cores and can't
get more because of the way PHP works - one thread per application.
Unfortunately, you don't have a lot of CPU headroom left to increase
the mail injection rate by running more SwiftMail engines in parallel.
You'll need to find a more efficient mail generator.
Wietse
