LARGE single-system Cyrus installs?
baconm at email.unc.edu
Fri Nov 16 11:59:51 EST 2007
--On Friday, November 16, 2007 7:39 AM +0100 Pascal Gienger
<Pascal.Gienger at uni-konstanz.de> wrote:
> Solaris 10 does this in my case. Via dtrace you'll see that open() on the
> mailboxes.db and read-calls do not exceed microsecond ranges.
> mailboxes.db is not the problem here. It is entirely cached and rarely
> written (creating, deleting and moving a mailbox).
This is where I think the actual user count may really influence this
behavior. On our system, during heavy times, we can see writes to the
mailboxes file separated by no more than 5-10 seconds.
If you're constantly freezing all cyrus processes for the duration of those
writes, and those writes are taking any appreciable time at all, you're
going to have a stuttering server with big load averages.
Again, it's not I/O throughput to be worried about here -- it's latency.
If you don't have write caches in front of your disk, even with RAID you're
still at the mercy of drive latency in the millisecond range. Not a
problem if those writes are once every five minutes, but if you're at peak
load on a big system and seeing them every couple of seconds, that's brutal.
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