v4: Max Children, sendmail QueueLA, RefuseLA

[Jeff A. Earickson]

Y'all,

   I upgraded from v3 to v4 last week with no major issues, until
our admissions office fired up their mass-mailer program for
prospective applicants.  It is one of these PC-based programs that
sends out one "customized" message per recipient, for 3K recipients.
Suffice to say that it bombs our mail server with messages.

   With a 2 CPU box (Sun E220R), I had "Max Children" set to 10.
With the incoming mass-mail, the system load quickly leveled off
at 14 to 16 with oodles of MS and sendmail processes, plus the usual
POP connections.  Then I noticed that email was backing up, and that
I was getting "connection refused" on SMTP connections.  I remembered
that my sendmail QueueLA setting was 14 and my RefuseLA was 16.

   So, my "Max Children" setting was high enough to bump up against
my sendmail load-average settings when MailScanner was maxxed out,
thus causing a degradation in mail service.

   I lowered "Max Children" to 4, reducing the total load to about 10
during the mass-mailing run, and things ran smoothly.

   Moral: take a look at your QueueLA and RefuseLA settings in sendmail.
Make sure that "Max Children" times the number of CPUS is less than
either of these two numbers, plus some breathing room.

-----------------------------------
Jeff A. Earickson, Ph.D
Senior UNIX Sysadmin and Email Guru
Information Technology Services
Colby College, 4214 Mayflower Hill,
Waterville ME, 04901-8842
phone: 207-872-3659 (fax = 3076)
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