[Mailman-Users] Mailman 2.1.6 slowness...?
brad at stop.mail-abuse.org
Sat Jul 16 15:51:45 CEST 2005
At 8:45 AM -0400 2005-07-16, Jeff Squyres wrote:
> Ah -- thanks for clarifying. This is not really what is implied in the
> FAQ (http://www.python.org/cgi-bin/faqw-mm.py?req=show&file=faq04.012.htp)
> -- I read it to imply that mailman is grouping messages to the MTA by
> domain in order to boost minimum number of deliveries to a given target
No. He's talking about the network bandwidth that will be used
by the MTA, once it has accepted all the messages and recipients from
Mailman. The MTA is forced to send no more than X recipients to a
given target site, because no more than X recipients exist at that
But Mailman could dump hundreds of thousands of recipients on the
local MTA, and not care about what the local MTA does with that.
We've been talking about the Mailman-to-MTA interface, not the
> That could simply be my flawed interpretation (I based that
> assumption on the bandwidth discussion in the middle), but perhaps it's
> worth a few clarifying statements in the FAQ...?
I'll see if I can come up with something.
>> If you break that up into smaller chunks, the system can be processing
>> more of those chunks in parallel, and each chunk can be accepted faster.
> We have pumped our SMTP_MAX_RCPTS down to 5 (we had never changed it
> before -- the mailman default was 500, even though the FAQ suggests
> that it should be significantly lower), but we'll have to wait for our
> next peak traffic period (likely not until Monday) to see how well
> it's actually working out.
One thing I would encourage you to do is to change just one thing
at a time, and see what the effects are. With regards to reducing
SMTP_MAX_RCPTS, I would encourage you to reduce the value by roughly
half at each stage. So, go from 500 to 250, 250 to 125, 125 to 62,
62 to 32, etc.... This way, you should get a better idea of what the
real threshold is.
> Right -- sorry, I didn't mean to imply otherwise. We were not surprised
> by this, either. I was trying to say that we've seen this behavior for
> a long time and didn't have any performance issues with it.
This sort of thing happens all the time with all sorts of
systems. People will notice that their tires seem a little low, and
there is some smoking coming out of the tailpipe, but they won't do
anything about it until the car blows up or the tires come off the
rims, etc.... That's when they take the car to the mechanic.
With computers, people may notice that queues get really long,
but they'll think that this is perfectly normal and acceptable, until
something bad happens. That's when they go looking for help.
They've been seeing all the signs that something bad was likely to
happen soon, but they didn't recognize them for what they were.
Sometimes it's expensive to fix catastrophic failures, sometimes
not. Unfortunately, this is the way that the world tends to work.
> The thought occurs to me that perhaps it wasn't our sendmail guys who
> changed something, but perhaps the guys in the anti-spam/virus-checking
> crew changed something (I believe they also check outgoing mails for
> some insundry list of things that they believe indicates spam/viruses).
> Hmm. Need to go ping them, too...
Yeah, gotta talk to them, too. The recommended practice for
mailing lists is to check messages on input, but don't try to check
them on output -- after all, the messages were already demonstrated
to be clean on input.
You may or may not be able to do this at your site, but you
should at least check with them.
The problem could also be DNS or reverse DNS. Those kinds of
things can really slow down MTAs, as they check their incoming
connections. If a DNS server is flaking out, the MTAs could be
taking much longer than they used to in order to do all the same
sorts of checks that they've always been doing.
Another thing to watch out for is tar-pitting SMTP services, such
as TarProxy (see <http://www.martiansoftware.com/tarproxy/>) or
OpenBSD's "spamd" (see
<http://www.benzedrine.cx/relaydb.html>). Note that "spamd" can also
be run on modern versions of FreeBSD that have also implemented the
"pf" firewall package that is also taken from OpenBSD.
This wouldn't directly affect Mailman, but could cause messages
to become backlogged on the MTA, waiting to be sent. You want to
keep a close eye on those MTAs, and you may want to make sure that
any tar-pitting is only done on inbound mail as opposed to outbound.
Brad Knowles, <brad at stop.mail-abuse.org>
"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."
-- Benjamin Franklin (1706-1790), reply of the Pennsylvania
Assembly to the Governor, November 11, 1755
SAGE member since 1995. See <http://www.sage.org/> for more info.
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