[imp] IMP performance under load

[Stephen Fischer]

quoth Chris Crowley:
| 
| The biggest performance loss is currently the IMAP server. We are currently
| looking at improvements for IMAP, any suggestions on this front are welcome.
| We also use sendmail, and POP3, so any IMAP servers would need to use a file
| format that is compatible.  I have read that indexed files will provide much
| quicker recall of user information.  But we have not yet determined a
| comprehensive plan for server improvements. Disk array on the mailserver
| should be optimized, too.

After quite a lot of testing, we're running the cyrus 1.6.24 IMAP software on
a Sun e450 with 4 cpus and 4GB of RAM.  It has a useable disk capacity of 250
GB, which is mirrored on an XSI array with weird and wondrous redundancy that
I know nothing about.  This talks to the rest of the world over a 100 Mbit
link.

Currently, we're getting a peak load of 1-2 with about 5000 POP connections
per hour.  The number of IMAP connections is negligible, since people have not
switched to using IMAP yet.  Under stress testing, we saturate the link long
before we start hammering the machine itself.

I'm quite happy about the speed and reliability of the cyrus software, and it
looked better than other ones I tested.

Stephen