[Dovecot] IMAP-proxy or not with sogo webmail and dovecot backend

[Michael M Slusarz]

Quoting Jan-Frode Myklebust <janfrode at tanso.net>:

> We've been collecting some stats to see what kind of benefits
> UP/SquirrelMail's IMAP Proxy in for our SOGo webmail users. Dovecot is
> running in High-performance mode http://wiki2.dovecot.org/LoginProcess
> with authentication caching http://wiki2.dovecot.org/Authentication/Caching
>
> During the weekend two servers (webmail3 and webmail4) has been running
> with local imapproxy and two servers without (webmail1 and webmail2). Each
> server has served about 1 million http requests, over 3 days.
>
> server          avg. response time	# requests
> ----------------------------------------------------
> webmail1.example.net   0.370411        1092386
> webmail2.example.net   0.374227        1045141
> webmail3.example.net   0.378097        1043919	imapproxy
> webmail4.example.net   0.378593        1028653	imapproxy
>
>
> ONLY requests that took more than 5 seconds to process:
>
> server          avg. response time      # requests
> ----------------------------------------------------
> webmail1.example.net   26.048          1125
> webmail2.example.net   26.2997         1080
> webmail3.example.net   28.5596         808	imapproxy
> webmail4.example.net   27.1004         964	imapproxy
>
> ONLY requests that took more than 10 seconds to process:
>
> server          avg. response time	# requests
> ----------------------------------------------------
> webmail1.example.net   49.1407         516
> webmail2.example.net   53.0139         459
> webmail3.example.net   59.7906         333	imapproxy
> webmail4.example.net   58.167          384	imapproxy
>
> The responstimes are not very fast, but they do seem to support
> the claim that an imapproxy isn't needed for dovecot.

Except you are most likely NOT leveraging the truly interesting part  
of imapproxy - the ability to restore the IMAP connection state via  
the XPROXYREUSE status response.  This is a significant performance  
improvement since it also reduces processing load on the client side  
(everything before/including authentication needs to be done whether  
using imapproxy or not, so there is no client-side savings for these  
commands).

For further information, see, e.g.:

http://lists.horde.org/archives/imp/Week-of-Mon-20110523/052316.html
http://lists.horde.org/archives/imp/Week-of-Mon-20110523/052317.html

These posts neglect the fact that you don't need to issue a CAPABILITY  
command if the connection is reused either, so that's an additional  
advantage. Note that the XPROXYREUSE-enabled MUA must be the exclusive  
user of the imapproxy instance for this feature to work correctly.

Somewhat topical, since Timo was just mentioning support for some sort  
of IMAP state save/restore feature possibly making it into 2.2.

michael