[horde] server capacity ?

Thu Nov 4 10:53:25 UTC 2010

Am Mittwoch 03 November 2010, 18:51:14 schrieb Michael M Slusarz:
> I personally develop with Dovecot for a variety of reasons.  Most  
> important is probably that Timo, author of dovecot, has optimized many  
> of dovecot's features/code specifically for problems unique to webmail  
> installations (he has been funded by several corporations primarily  
> for this reason).  Server-side caching may be the most important of  
> these optimizations - this is critically important for webmail  
> installations.
> 
> Additionally, with Dovecot 2 Timo has implemented several IMAP  
> extensions that are tremendously useful for disconnected clients (of  
> which webmail is a specialized type).  In IMP 5, we make full use of  
> these extensions to optimize caching and provide a truly transparent  
> caching experience - a stock RFC 3501 IMAP client has certain  
> limitations that don't allow seamless caching (e.g. flag changes can  
> not be synchronized if another IMAP client changes the mailbox).

hmmm,
as far is i had / can read until now there (i mean many ressources where 
dovecot are compared to cyrus and others) are some misunderstandings in the 
Cyrus concept. Cyrus is not a typical maildir server. 

Wonder why, this seems very typical on some current open source projects, 
where someone told's - that is "the best" (without really knowing the 
alternatives) - while the main success of the app just comes from an easy 
installation. But, installation is not all...

Cyrus still uses indexes ("caches") since many years which makes possible to 
run a high load / entersprise pop3/imap system very fast. Indices could be 
reconstructed and maintained in several ways and the admin has different 
abilities to handle that. Critical (central) indexes are typically backed up 
at least by cyrus services - could be stored in different DBs or file formats.

The target of a system like cyrus is to offer a reliable, standard compliant 
pop3 / imap service - independently from which client a user uses sometimes or 
every time (like dovecot). I'm not a friend of mixing tasks between servers 
and clients in a standard service environment.

Caching with cyrus is typically done "quasi-automatically" by the OS with OS 
dependent caches in RAM. Authentication caches typically could run in a 
database or in saslauthd. The sysadmin could define where and how caching is 
wanted by OS and applicational functionality - but this may require some 
deeper system or application knowledge sometimes.

btw:
"To much" caching could bring negative experiences up to collisions in 
uncalculable environments - so such apps should strictly go along the 
standards / protocols.

In cases where users are mainly using WebMail dovecot may (!) offer a better 
performance in many situations - but if you operate as an open email provider 
which allows and assumes that users are using any different imap clients (and 
change them less or more often). I did not understand why a standard protocol 
server should take care of any special standard compliant client?

I know several cyrus installations which are handling then or hundredthousands 
of mailboxes (or even millions of). If dovecot is on the way to the core app 
at such larger email service providers over some years it may get my trust too 
on that level ;) - afaik that is not the case currently...

Shure, even cyrus has something which could ger maked better and/or faster 
(i.e. within the fulltext indexes) - but (please) independent from any clients 
around...

Cyrus is - in some parts - a black box, but this is dovecot too (and getting 
more as far as i see current developements / roadmaps)...

One major thing may be is that dovecot is more easy to install (what could be 
important for "smaller" users / environments). Apps like cyrus, exim and 
others are very flexible and complex - so the users has to decide things where 
dovecot did not allow alternatives...

If dovecot could give here more reliability, flexibility and performance in 
the future - i will switch to it asap, no question.

just my two cents,

Niels.

-- 

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  Niels Dettenbach
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  Syndicat IT&Internet
  http://www.syndicat.com
  T.-Muentzer.-Str. 2, 37308 Heilbad Heiligenstadt - DE
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