Large Mailman posting causes sluggish server, 70 load!

[sneader]

Hey there! I'm looking for some ideas on tweaking performance of
Mailman and Exim. Here's the situation:

I have a customer that sends out one message per day via Mailman. This message usually has some HTML and is typically 100KB or more. There are over 12,000 subscribers.

A year ago, the customer complained about excessive delivery times for the
messages. I checked the Exim logs, and saw this repeatedly in the logs, during the queue runs:

[7377] 1KmsZI-0001uz-Dv no immediate delivery: more than 10 messages received in one connection

Doing some research on this, I found that I needed to tweak the Mailman
config. I edited /usr/local/cpanel/3rdparty/mailman/Mailman/mm_cfg.py to add:

# Max recipients for each message
SMTP_MAX_RCPTS = 10

# Max messages sent in each SMTP connection
SMTP_MAX_SESSIONS_PER_CONNECTION = 10

This solved the delivery problem... messages now get delivered pretty quickly
and the customer is happy.

However, when the customer sends their message, the server goes into a coma, often reaching 20.0 to 70.0 Load average! It usually causes pages to be served very sluggishly, or to outright fail. My http monitor usually goes off, but recovers after a few minutes.

I have not experimented with removing the Mailman config tweaks, to see if it
solves the load problem, because then it causes excessive delays in mail delivery for my customer.

Open to suggestions (except moving them to phpList -- tried that once, did not go well, LOL)

P.S. I have a ps output from the high load time, but it has a lot of usernames and paths in it, and don't want to post in the public forum. If you think it would be useful and want to see it, PM me for it.

Thanks!!

- Scott

[sneader]

I should have mentioned more about the server.

cPanel 11.24.5 Latest Stable (38506)
CentOS 5.3 / 64-bit
Q6600 Quad Core CPU @ 2.40GHz
8GB Memory

Last 24 hours: Average 5-minute load = 0.54

Some load and process information captured during 3 recent mailings by this customer:

Time: Mon Jan 18 10:18:07 2010 -0600
1 Min Load Avg: 36.52
5 Min Load Avg: 9.21
15 Min Load Avg: 3.37
Running/Total Processes: 2/2942

Time: Sun Jan 17 22:26:48 2010 -0600
1 Min Load Avg: 69.07
5 Min Load Avg: 16.38
15 Min Load Avg: 5.59
Running/Total Processes: 2/3033

Time: Wed Jan 13 09:42:16 2010 -0600
1 Min Load Avg: 32.90
5 Min Load Avg: 11.85
15 Min Load Avg: 4.71
Running/Total Processes: 2/2550