Discussion:
[Mimedefang] MIMEDefang Digest, Vol 165, Issue 5
Amit Gupta
2017-08-29 03:49:41 UTC
Permalink
Thanks Dianne! Our server has 16GB of ram and we have a 2GB RAMDISK
setup for md.

In the multiplexor man page, I saw this quote:
"Using the -R option has the side-effect of permitting new connections from
the loopback address to queue." Does this mean you can have loopback
connections queue and non-loopback connections get a standard busy
warning if the max processes are used up?


Regarding your comment about the downside is that it would "Hold open
more connections and use more milter threads." I wasn't quite sure
what you meant by "using more milter threads"? Do you mean that it
will just use MX_MAXIMUM mimedefang.pl processes for longer? ie, until
the traffic spike is fully processed?
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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Dianne Skoll
2017-08-29 13:19:47 UTC
Permalink
On Mon, 28 Aug 2017 20:49:41 -0700
Post by Amit Gupta
Regarding your comment about the downside is that it would "Hold open
more connections and use more milter threads." I wasn't quite sure
what you meant by "using more milter threads"?
mimedefang (the C program, as distinct from mimedefang-multiplexor) is
multi-threaded, and it holds open a thread for each active SMTP session.
So there will be more threads active if sessions are queued than if you
don't queue sessions.

Regards,

Dianne.
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