v4: Max Children, sendmail QueueLA, RefuseLA

Julian Field mailscanner at ecs.soton.ac.uk
Tue Nov 26 18:34:03 GMT 2002

At 17:54 26/11/2002, you wrote:
>    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.

As many of the MailScanner processes will be sitting in "network waits" the
high load figure you see is nothing to be afraid of. On my test server I
jacked up the QueueLA and RefuseLA figures to 20 or 30.

Lots of MailScanner children will create a high load average if hit hard,
make sure your system is correctly configured to handle it.
Julian Field                Teaching Systems Manager
jkf at ecs.soton.ac.uk         Dept. of Electronics & Computer Science
Tel. 023 8059 2817          University of Southampton
                             Southampton SO17 1BJ

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