[Mimedefang] tmpfs on Linux

[Cormack, Ken]

It is likely that your tmpfs (ramdisk) is too big for the amount of total
physical RAM installed in the system.  Secondly, you don't state how many
concurrent processes you are running, and so on.

The system will swap when it runs low on usable RAM.  Whatever RAM you've
dedicated to the tmpfs is not otherwise "useable" to the running programs.
Thus, paging/swapping occurs.

Add more RAM to the system, and take a good practical look at how big your
ramdisk truly needs to be.  I know the worst-case calculation says to
multiply the max message size by the max number of allowed child processes.
However, it has been my experience that I in no way need a RAM disk of 2GB,
which is equal to 50MB (my max message size) x 40 (max concurrent child
processes).  My average message size lately has been around 46K.  And as
rare as it is for me to receive a single 50MB email, I have not yet seen an
instance where I've had to process 2 messages of that size, concurrently
(though I have seen a mix of 10, 15, 4, and 30MB messages all at once, for
example.)  My RAMdisk is set to 128MB, and I have only seen it go 100% full
once or twice, in my daily reports.  In those cases, the messages were
tempfailed by MIMEDefang, and succesfully re-transmitted on the next attempt
by the sending servers.  As an example (from last night's report of
yesterday's traffic), this configuration succesfully handles the following
message rates, on a 2GB dual-proc system:

AVERAGE RATE - MESSAGES PER MINUTE
  MIDNIGHT-8AM: 36
       8AM-5PM: 104
  5PM-MIDNIGHT: 50
       24 HOUR: 66

TOP 10 BUSIEST MINUTES:
  278 Msgs/Min @ 10:27
  275 Msgs/Min @ 10:21
  263 Msgs/Min @ 10:33
  255 Msgs/Min @ 10:32
  253 Msgs/Min @ 10:31
  251 Msgs/Min @ 10:26
  250 Msgs/Min @ 10:23
  247 Msgs/Min @ 10:25
  246 Msgs/Min @ 10:29

PEAK RAMDISK UTILIZATION: 53%
Time of Peak Utilization: 15:30

Ken

-----Original Message-----
From: Greg Miller [mailto:gmiller at richmond.edu] 
Sent: Wednesday, November 10, 2004 9:05 AM
To: mimedefang at lists.roaringpenguin.com
Subject: [Mimedefang] tmpfs on Linux


Platform is RedHat EL AS 3
Dual Xeon 3.0 Ghz CPU
1 GB RAM
Load is between 1-3 messages per second.

System performs very well, most of the time, with only 2-3 busy slaves.
However, on occasion, I will see all 15 of my slaves busy, lots of disk
I/O to swap, and "Please try again later" messages in the maillog.

I am using tmpfs for /var/spool/MIMEDEFANG as recommended in the FAQ. I
believe my tmpfs is being sent to swap during these periods and causing
horrible performance.

Has anyone else seen this behavior? Any solutions out there?
Thanks.

-- 
Greg Miller, RHCE, CCNA, MCSE
Senior Network Specialist
University of Richmond
gmiller at richmond.edu
(804) 289-8546
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