[Mimedefang] ALLOW_NEW_CONNECTIONS_TO_QUEUE behavior

[Dianne Skoll]

On Sat, 26 Aug 2017 22:52:15 -0700
Amit Gupta <amit777 at gmail.com> wrote:

> Assume a burst of emails comes in and all 20 md processes are busy
> working.

> 1) What should the 21st and higher connecting  clients
> experience?

Sendmail will appear to respond more slowly than usual.

> 2) Is there a configurable limit to the number of queued
> connections?

Yep.  The "-q" option to mimedefang-multiplexor.  See the -q and -Q
command-line options in the mimedefang-multiplexor(8) man page.

> 3) What's the downside of letting the connections queue
> other than holding open more TCP connections?

Holding open more connections and using more milter threads.

> 4) Any other tips on the settings you use in production?

If you actually need to queue requests more than occasionally, you
need a more powerful server.  The queueing feature is supposed to handle
transient bursts of traffic.  It isn't meant to squeeze more steady-state
performance out of a server.

> The reason I'm asking is because we recently had a burst of traffic
> that caused the IO on our server to go up to a point where everything
> became unresponsive for a couple minutes.  We had our MX_MAXIMUM set
> to 110.

How much RAM did you have?  You really, really, really don't want a
MIMEDefang scanning server to start swapping.

Regards,

Dianne.