idled vs poll

[Sebastian Hagedorn]

--On 18. Oktober 2006 11:25:09 +0100 Adam Stephens 
<Adam.Stephens at bristol.ac.uk> wrote:

> We deployed idled here over the summer on our main staff IMAP server, a
> Sunfire v480 running Solaris 8 and cyrus-imap 2.2.12. It typically has
> about 13,000 concurrent IMAP processes

Wow, that's a lot of sessions! I'm surprised about that. We have about 
35,000 users, yet we rarely have more than 700 concurrent IMAP processes. 
Partially that's because our Webmail system, which is surprisingly popular, 
doesn't cache sessions. But the majority of users use POP anyway.

> Initially, we saw a small rise in the server load, which wasn't
> particularly worrying, and occasionally slightly more worrying sluggish
> authentication. Last week was the start of term, and the system collapsed
> completely. The load average rose from about 1 to between 6 and 9,

That's not really such a high load, although that depends on the number of 
processors your server has.

> This left the system almost completely unusable. We tried various things
> to fix it, to no avail. Last night we rebuilt Cyrus with with-idle=poll;
> the load is immediately much lower (currently 0.7), authentication and
> IMAP are vastly more responsive and there are no socket errors logged.

Surprising, but good to know for future reference.
-- 
     .:.Sebastian Hagedorn - RZKR-R1 (Gebäude 52), Zimmer 18.:.
Zentrum für angewandte Informatik - Universitätsweiter Service RRZK
.:.Universität zu Köln / Cologne University - ✆ +49-221-478-5587.:.
                   .:.:.:.Skype: shagedorn.:.:.:.
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