[Mimedefang] Understanding the -q flag

[Amit Gupta]

I saw in the documentation that the -q flag will allow mimedefang to
accept more connections than the number of mimedefang slaves and it
will queue connections if the slave limit is exceeded. I wanted to
understand the implications and potential downsides of enabling this
better..

So if your slave limit is 100 and they are all processing emails, but
you need to process 500 emails that moment, does this mean 400 emails
will be queued for processing as soon as the slaves start freeing up?
Does this open up a potential denial of service attack? or is it
relatively light-weight to keep a connection in queue? Any other
gotchas we should be aware of that may not be explicitly mentioned in
the docs?

Thank you!
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[Dianne Skoll]

On Tue, 5 Jan 2016 12:16:49 -0800

Post by Amit Gupta
So if your slave limit is 100 and they are all processing emails, but
you need to process 500 emails that moment, does this mean 400 emails
will be queued for processing as soon as the slaves start freeing up?

Yes. However, with those specific numbers you're in trouble because
it's highly unlikely all 400 of the queued connections will be handled
in a timely manner. Most likely, the senders will time out first.

The -q option is meant to be used only to slightly increase the peak
message counts that MIMEDefang can handle in the face of occasional
load spikes. Having a -q more than about 10% of your max slave count,
or more than about 40 in absolute terms, is likely to be
counter-productive.

Regards,

Dianne.
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