Re: [Mimedefang] ALLOW_NEW_CONNECTIONS_TO_QUEUE behavior

[Dianne Skoll]

On Sat, 26 Aug 2017 22:52:15 -0700
Amit Gupta  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.
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[Mimedefang] ALLOW_NEW_CONNECTIONS_TO_QUEUE behavior

[Amit Gupta]

Hi, I wanted to get a better understanding of of the nuances of
ALLOW_NEW_CONNECTIONS_TO_QUEUE in a high volume burst scenario.

MX_MAXIMUM=20
MX_QUEUE_TIMEOUT=300

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?
2) Is there a configurable limit to the number of queued connections?
3) What's the downside of letting the connections queue other than
holding open more TCP connections?
4) Any other tips on the settings you use in production?

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.
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message, it is NULL AND VOID.  You may ignore it.

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