On Wed, Jan 23, 2013 at 1:55 PM, Andrew Morgan <morgan@xxxxxxxx> wrote:
You can certainly achieve higher delivery rates, but that all depends on your underlying hardware and how you have partitioned your system.On Wed, 23 Jan 2013, francis picabia wrote:
Here are more stats. Do these look average for performance?
It is difficult to understand why the system was working with few
load spikes before.
A mailman mailing list sends 10kbyte message to 4000
users having accounts on this cyrus system. If I
grep "Delivered" in the maillog by the minute I can
see how fast the messages are stored.
e.g.:
# grep Delivered /var/log/maillog | grep 'Jan 23 10:37' | wc -l
696
That is the best. This peak event pushed the load to 14
for 12 minutes, where it averages 604 messages
delivered to cyrus mailboxes per minute. Is that
reasonable for maximum delivery rate?
I've also backed out the change (yesterday) to
/sys/block/sda/queue/nr_requests
I think it was pushing the load higher and there is no advantage
in my hardware (SAS with Perc 5/i Raid 5 over 4 disk)
to run with a low value for nr_requests.
Why don't you start running "iostat -x 5" on the system? Leave this running to give you an idea of the baseline behavior and then look at it during periods of high load. I suspect you will see that your svctm and %util will go up dramatically when a large number of messages are being delivered. But, let's not make decisions based on assumptions! :)
On my Cyrus Murder frontends (3 of them), I have limited LMTP connections to 25 in cyrus.conf:
lmtp cmd="/usr/local/cyrus/bin/lmtpproxyd" listen="lmtp" proto="tcp4" prefork=0 maxchild=25
This prevents our mail relays (Postfix) from opening too many simultaneous LMTP connections, which can cause too much I/O contention. Take a look during your periods of high load to see how many lmtpd processes are running. You may want to limit the number.
Andy
Thanks for the response. I have been checking my iostat whenever there is
a number of messages in the active queue.
Here is a sample snapshot from a script I run (ignoring the first
iostat output of averages):
Active in queue: 193
12:47:01 up 5 days, 5:23, 6 users, load average: 14.11, 9.22, 4.67
Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz avgqu-sz await svctm %util
sda5 3.25 281.00 19.75 129.50 654.00 3384.00 27.06 5.53 36.24 6.69 99.80
svctm is about the same as when not under load and it went above 7 only once.
Then there is this comment about the validity of tracking svctm:
http://www.xaprb.com/blog/2010/09/06/beware-of-svctm-in-linuxs-iostat/
%util is often reaching close to %100 when there is a queue to process.
sda5 is where the cyrus mail/imap lives. Our account names all begin with
numbers, so almost all mail accounts are under the q folder.
I'll check the lmtp process numbers as well. I've put in some in_flow_delay on the
postfix side so it might keep the load from peaking as sharply.
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