dovecot - Jun 2012 - Dovecot performance under high load (vs. Courier)

Hi,

We are building a new system that will support a large number of users (high
volume, high concurrent usage, etc).? We have played with Dovecot, but in most
serious applications we have traditionally used Courier IMAP.? It's my (lay)
understanding that with indexing and perhaps other things in Dovecot, it might
perform better than Courier in larger environments like this.? Am I correct or
is it less clear-cut?

Any tips on making the migration (not migrating an existing system, I mean
migrating our paradigm - things to consider, things to watch out for)?

TIA

On 21.6.2012, at 21.05, email builder wrote:
> We are building a new system that will support a large number of users
(high volume, high concurrent usage, etc).  We have played with Dovecot, but in
most serious applications we have traditionally used Courier IMAP.  It's my
(lay) understanding that with indexing and perhaps other things in Dovecot, it
might perform better than Courier in larger environments like this.  Am I
correct or is it less clear-cut?
If you disable index index files in Dovecot, its performance should be slightly
better than Courier. With index files the performance is typically much better
in Dovecot, especially if you use a (non-caching) webmail.
> Any tips on making the migration (not migrating an existing system, I mean
migrating our paradigm - things to consider, things to watch out for)?
If you don't migrate any existing users, I guess this doesn't differ
much from any other optimized Dovecot installation. Usually large installations
(>1M users) use NetApp NFS + Dovecot director. You might also want to enable
full text searches. http://wiki2.dovecot.org/PerformanceTuning lists some other
things.

Quoting Ed W <lists at wildgooses.com>:
> I think the conclusion is that imapproxy is not necessary.  There  
> are some advantages (eg with high network latency between web and  
> imap server, and reducing apparent login count), and some  
> disadvantages (extra complexity, slowdown)
Not entirely true.  See this thread:

http://markmail.org/thread/z7ctwle2go6zafas

Thread in short: imapproxy provides benefits for more MUAs that take  
advantage of the XIMAPPROXY feature (only IMP, AFAIK), and Timo is/was  
considering adding a similar state saving feature to Dovecot 2.2.

michael

>
> We are building a new system that will support a large number of users
(high volume, high concurrent usage, etc).
what is large?
>? We have played with Dovecot, but in most serious applications we have
traditionally used Courier IMAP.
>? It's my (lay) understanding that with indexing and perhaps other
things
>in Dovecot, it might perform better than Courier in larger environments 
>like this.? Am I correct or is it less clear-cut?
No idea how well courier IMAP performs. But have idea how well dovecot 
performs. I don't have large configs like thousands of users as i don't 
handle "herd of random users" style cases, but in every place i have 
dovecot IMAP takes unnoticable amount of server load.

Just make a test.

Definitely use maildir format, not mbox.

dovecot heavily accesses it's index files. they are not large relative to 
e-mail sizes. With really large case if I/O will limit you i would 
recommend using SSD storage to keep just indexes.