On Thu, 19 Oct 2006, Michael Loftis wrote:
--On October 19, 2006 11:25:07 PM +0200 Marten Lehmann <lehmann@xxxxxx>
wrote:
Hello,
Uhm... LA of 30 is very high. What OS? I assume Linux, vmstat 5 will
tell you where you're hitting the wall, but unless you've got an 8 CPU
machine LA 30 is rather quite high. Linux LA is a measurement of
processes blocked on I/O, processes running and processes waiting to run
on a CPU.
yes, Linux (2.6.9, RHEL4):
Looking at taht i'd say you're VERY badly CPU bound. a simple dd/cp doesn't
do anything to the mail but IMAP ops will require some CPU work....Cyrus also
will probably be forcing syncs but your I/O load doesn't look that high (my
mfe's run more I/O and they're not storing any mail, just logs and temporary
files for virus/spam scanning heh, and they only have a little IDE HDD each)
the numebrs in the procs->r column indicate you've got a lot of processes
vying for CPU time. the b column indicates you've got a little bit of
blocking going on. Processes in the 'D' state may show up in ps or top
output (doubtfully top unless you change the default sort).
I'd guess you're being CPU bound and cyrus is probably running (usually does
by default) at a bit lower priority than your interactive cp operations. 2.6
kernel scheduler does a lot of weird stuff if it determines you're
interactive, and then tends to give you priority over daemons. it's very
non-deterministic, but I don't think you're running into this. quite likely
some inefficiencies in the cyrus code (or intentional backoffs?) but mostly
just being CPU bound. I know our MBEs can generally scp or rsync quite a bit
faster than they can perform a XFER/RENAME command that moves between mail
store servers (IE MURDER host to MURDER host).
No clue if it matters in this imapsync case, but if you are using the 2.6
kernel, you should set the I/O scheduler to "deadline" rather than the
default "anticipatory". You can set this in the boot loader, such as the
following for lilo.conf:
append="elevator=deadline"
or you can change the scheduler on the fly by:
echo "deadline" > /sys/block/sdb/queue/scheduler
Replace "sdb" with the block device you store your cyrus mail spool on.
Andy
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