[Mailman-Users] Big Lists

Chuq Von Rospach chuqui at plaidworks.com
Tue Dec 18 19:39:39 CET 2001

On 12/18/01 5:06 AM, "Tass" <tass at kenderhome.com> wrote:

>> default_process_limit = 150
> If you have 512M of Ram set it to 200, it will give you a lot of room.

Maybe. Maybe not. 

One of the things you need to do when setting up your MTA is figure out what
your network can take. It makes no sense (in fact, it hurts throughput
significantly) if you have more processes attempting to send mail than your
network can handle.

If you're on a 384K DSL, you have to tune much different than if you're on
an T1. And you're gated by your slowest link, not your closest one.

One of the things you need to do, then, is try increasingly large numbers of
parallel delivery processes, and watch your network patterns. What I usually
do is look for when dropped packets and/or retries start going up. Once you
get there, you've basically saturated your slowest network link, bceause
stuff is disappearing into the void. Once that happens, your overall
throughput will start going down, because your processes will be fighting
for the network, losing packets, retrying, waiting for each other's packets
to get out of the way, and generally creating minor chaos at the TCP layer.

So what I do is I ramp up delivery until this point happens, then back it
off by about 10%. If (as with the SSH guys a couple of days ago) you want to
reserve more bandwidth, back it off more.

A really rough way to estimate this, if you don't want to get nerdy, is to
use "ping". Ping, for instance, the router on the far side of your WAN link,
and wait for packets to start dropping. That'll tell you when that link
fills up. 

If you're seeing significant collisions, retries or dropped packets, you're
overfilling your network and hurting performance. Better 50 mail processes
cooperating than 60 getting in each other's way. And I think it's best to
manage this by rate-limiting the MTA, which you can test and tune fairly

>> disable_dns_lookups = yes
> I have found this to be no real change.
> On a PIII-500 with 512M I am getting 100K-120K/hr on a T1 connection with
> avg message of 6.1K.

Then I'd guess you have a fairly small group of domains you deal with. The
wider your subscribers wander, especially if you cross continents, the more
you'll see issues with slow DNS. Better to turn it off and let the Mta deal
with it asynchronously.

> If most of your email is going to a few domains that you know are good at
> handling email you can also set
> default_destination_concurrency_limit = 15

As long as you don't flood them and piss them off. Be careful over-ramping
to a single domain.

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