[Mailman-Users] How to clear queue?

[Brad Knowles]

At 3:27 PM -0700 2005-05-09, Tyler Strickland wrote:

>  That's entirely possible - the system is an old sun running sendmail.

	Older versions of sendmail can certainly have some issues in this 
respect.  More modern versions work much better, but still require 
some additional configuration changes in order to get them to work 
better with large mailing lists.

>  I'm currently building a new mail server to replace it that should be
>  able to handle the load much better by running postfix on a
>  hyperthreaded Pentium 4.

	See the stuff in the FAQ about "performance".

	For one, HyperThreading almost always hurts performance and does 
not help.  This is a seriously dain-bramaged idea that Intel had that 
never panned out, although they did get enough people interested in 
the concept that once AMD came out with a real dual-core chip, 
performance really has improved significantly.


	For two, you don't need CPU.  You need RAM and disk I/O capacity. 
Not disk space, but I/O capacity.  When an MTA receives a mail 
message, it creates one or more temporary files to store that 
message.  When the message has been delivered, the temporary files 
are deleted.  Between those two points, there may be many more file 
creations, deletions, and renaming operations just for that one 
message.

	Each of these types of operations are known as Synchronous 
Meta-Data Operations, and they require that the entire directory be 
locked against all other changes during the process of that 
operation.  You would think that this would not hurt performance very 
much, but think of a turnstile going into a football stadium -- no 
matter how fast it operates, the simple fact that it only allows 
through one person at a time will mean that the total throughput is 
greatly reduced.

	A fast intelligent hardware RAID array with a large quantity of 
battery-backed write-back RAM cache and high-speed internal 
interfaces to high-speed drives with intelligent disk queueing (i.e., 
SCSI with Tagged Command Queueing, or good SATA drives that actually 
properly implement a similar feature) can really help.  A fast 
filesystem which optimizes synchronous meta-data operations can also 
help.


	But all this is covered in the FAQ, and you should read about it 
when you search for "performance".

	I will tell you that if you're trying to build a high-performance 
mail/mailing list server, about the worst possible mistake you could 
make would be to try to build the machine without first reading the 
information on this subject in the FAQ, and reading the various 
pieces of documentation that are referenced.

-- 
Brad Knowles, <brad at stop.mail-abuse.org>

"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."

     -- Benjamin Franklin (1706-1790), reply of the Pennsylvania
     Assembly to the Governor, November 11, 1755

   SAGE member since 1995.  See <http://www.sage.org/> for more info.