[Mimedefang] Sendmail bug with multiple queue directories

[Nik Clayton]

Hi all,

I know it's not directly relevant, but since everyone here is using 
Sendmail[1] it probably affects you, so I hope David doesn't mind.

As documented, if you have multiple queue directories (e.g., 
/var/spool/mqueue/qdir00, qdir01, qdir02, etc), and QueueDirectory 
specification that has a wildcard (like /var/spool/mqueue/qdir*), 
Sendmail is supposed to create one queue runner process per directory.

So if you have 5 directories, "sendmail -bd -q15m" will create 5 queue 
runners every 15 minutes.  This is covered in the Sendmail 
documentation, and in the book "Sendmail Performance Tuning", which 
talks about N directories letting you process the queue in potentially 
1/N the time it would take if you only had 1 directory.

In the course of doing some testing with DTrace I've discovered that 
Sendmail doesn't do that, and probably hasn't behaved like that since 
queue groups were introduced.  Sendmail will only create one queue 
runner, irrespective of how many directories you have.

Details at:

http://jc.ngo.org.uk/blog/2006/08/19/day-41-of-60-multiple-queues-multiple-queue-runners-pt-2/

http://jc.ngo.org.uk/blog/2006/08/21/day-43-of-60-multiple-queues-multiple-queue-runners-pt-3/

This can have a significant performance impact if you have large queues.

N

[1] Unless anyone's using MIMEDefang with Postfix's milter interface