Debugging and resolving high loadavg when running MailScanner
Steen, Glenn
Glenn.Steen at AP1.SE
Wed Feb 16 14:50:29 GMT 2005
Ok. That's at least an indication that "peaks" might not be handled that
well.
Do take a look at getting some form of "baseline" for vmstat and sar
established, so
that you can compare to what you have during "slowdown"/peaks. What is
normal
for one system might be spelled o-v-e-r-l-o-a-d on another:-).
BTW Just trying to help here, not snub you in any way. Not being native
to the english language
has been noted to make me look to be in the "jerk department" from time
to time:).
Regards
-- Glenn
-----Original Message-----
From: MailScanner mailing list [mailto:MAILSCANNER at JISCMAIL.AC.UK]
On Behalf Of Richard Curtis
Sent: den 16 februari 2005 15:39
To: MAILSCANNER at JISCMAIL.AC.UK
Subject: Re: Debugging and resolving high loadavg when running
MailScanner
I am not claiming to be a master admin or anything - I am just
trying to solve what I believe to be a problem using what I know to
the best of my abilities.
The reason that I percieve there to be a problem is that when the
load goes high, web page serving and even ssh logins can take a
long period of time. That is what led me to beleive there is an
issue.
I will go and look into the tools such as SAR that you mentioned
and see what I can establish from that.
Thanks for the advice... Im still learning and just trying to work
out issues as I find them...
Richard
Excuse me, but why are you "hung up" on loadfactor as a
performance meter?
It is just the average run queue size (averaged over 1, 5 and
15 minutes), and as such is meant
to vary.
You say you have a 2 CPU system, in which case (with a "SMP
capable" kernel) you'd be fine
with anything up to 2 in a "sustained load" (meaning more
than in transient peaks).
Add to this that processes in "non-interruptible wait"
(usually for IO resources) add an unconditional
1 (one) each, it is not at all surprising that the load goes
a bit beyond your "CPU count" when you
have a larger batch of messages coming in.
Unless you perceive true slowdowns, you don't really have a
problem with that.
Now, the swap bit _could_ be an indicator of true problems...
You say you use it for other things than
as a mailhub... So you might be in a slightly memory starved
state, easily determined via vmstat or sar,
if you have a fair amount of ongoing swapping.
But using swap on a system that runs for an extended period
of time is usually not an indicator of
problems in and of itself, it is the actual moving to/from
swap of frequently used memory slices that'll
be a killer.
If you can determine that you have this situation, you have
only two venues: reduce the RAM usage
(by reducing what the machine does), or add more RAM.
Nothing you've said so far indicate that you do have a
problem... Does the machine occasionally
slow down in a perceptible and measurable way? Does
MailScanner report huge batches?
I'd like to recommend the excellent "swordfish book" from
o'rielly (Systems performance tuning).
Even though it is geared toward Solaris primarily and linux
(2.4) secondarily, it has a lot of general
good tips (and tool usage tips that are rather generic for
most unices).
-- Glenn
-----Original Message-----
From: MailScanner mailing list
[mailto:MAILSCANNER at JISCMAIL.AC.UK] On Behalf Of
Richard Curtis
Sent: den 16 februari 2005 13:04
To: MAILSCANNER at JISCMAIL.AC.UK
Subject: Re: Debugging and resolving high loadavg when
running MailScanner
I am not using either... running
spamassassin -D --lint -p
/etc/MailScanner/spam.assassin.prefs.conf says there
are two problems - but the two problems appear to be
that razor and pyzor are not installed..
The load is sitting at around 0.5 at the moment - but
when I was looking about 5 minutes ago it shot to 5.0
when a large batch of email came in.
I am wondering if I need to do something with the
number of children. I currently have it set to 10 -
based on the reccomendation of 5 per cpu.
The other thing I think might be related to my problems
are the fact that the system is using a fair amount of
swap - would that contribute to the load ?
Rich
Are you using razor or pyzor in that setup and
does
spamassassin -D --lint -p
/etc/MailScanner/spam.assassin.prefs.conf
show any problems with either of these?
If so,
razor-admin -discover
pyzor discover
might be useful (I've put them in a cron job
here).
Cheers,
Phil
----
Phil Randal
Network Engineer
Herefordshire Council
Hereford, UK
________________________________________________________________________________
From: MailScanner mailing list
[mailto:MAILSCANNER at JISCMAIL.AC.UK] On
Behalf Of Richard Curtis
Sent: 16 February 2005 11:33
To: MAILSCANNER at JISCMAIL.AC.UK
Subject: Debugging and resolving high
loadavg when running MailScanner
Hi All,
I have been running MailScanner (Version
4.35.11) for some time, but over the last 2
-3 weeks, my loadavg has gone from
~0.10-0.20 to as high as 4. This may not
seem high to some, but as I have other
services on this box I want to try to
reduce the load.
The box runs httpd, sendmail/MailScanner
with clamav, radius and pop. There are
multiple hosted domains on the server.
The box is a dual AMD Athlon MP 1200 with
512MB RAM.
All mail is scanned through MailScanner for
virus's, but only a small number of the
domains (low traffic ones) have
SpamAssassin enabled in MailScanners
configs.
I have to admit that I am a bit confused by
some of the MailScanner config options -
for example, the effects of "Deliver In
Background = yes" and "Delivery Method =
batch".
By setting the delivery method to queue,
what kind of impact on delivery time can I
expect ? Will this have a significant
effect of lowering the load ?
One other question, I note from looking
through the logs, I see entries like:
Feb 16 11:25:32 lancelot MailScanner[7544]:
New Batch: Scanning 1 messages, 1720 bytes
Feb 16 11:25:32 lancelot MailScanner[7544]:
MCP Checks completed at 1720 bytes per
second
Feb 16 11:25:32 lancelot MailScanner[7544]:
Spam Checks completed at 1720 bytes per
second
Now what confuses me here is that I have
MCP checks and Spam checks set to off for
this mail domain - so why are the checks
happening ?
Any suggestions on performance tuning of
MailScanner, or possible sendmail config
tweaks would be greatly appreciated.
Regards
Richard
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