[Dovecot] A large number of imap processes
tss at iki.fi
Thu Apr 24 16:40:34 EEST 2008
On Fri, 2008-04-18 at 14:14 +0200, Claude Frantz wrote:
> When a large number of messages for many different users arrive nearly
> at the same time (e.g. a message to all the users), a large number of
> sleeping processes become active, the CPU usage increases to more than
> 80 or 90 % and the LA can be many hundreds for a long time. The machine
> is not more really operational from user's point of view. NFS is
> probably a problem here, but some NFS tests have not allowed to discover
> problems at this level. Now, I'm trying to find a "solution" in the way
> to delay the delivery of the messages to the maildirs. I think, it is
> not really a nice solution.
> I think that the large number of now running processes is the rebuilding
> of the index. I am right here, Timo ?
Index updates typically don't take long. Although if client fetches some
metadata that isn't in cache file, Dovecot needs to open the messages
and parse them. That takes some I/O. This can be avoided with v1.1 by
using deliver, since it updates the cache file immediately.
Although I'm still not sure if that would help, because a lot of clients
just download the entire message body automatically, which in any case
> At the present time, the mailfilter language of
> maildrop (and Courier) is used here in place of procmail used in the
> past. I ignore if using dovecot's LDA could be a solution in this
> environment. But the mailfilter language could be a problem. A migration
> to sieve is not really a choice, in my opinion. I have never seen a good
> sieve script testing software.
Can you tell maildrop to deliver the message to a specific mailbox using
an external command (i.e. calling deliver) instead of delivering itself?
Probably wouldn't be a difficult change to the code if it doesn't
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