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From Bernd Fondermann <bf_...@brainlounge.de>
Subject Re: IMAP Draft: Cluster
Date Sat, 08 Jul 2006 10:56:14 GMT
Joachim Draeger wrote:
> Hi Bernd,
>>>Imap is quite resource intensive. 
>>Is it? Why?
>>How does IMAP resource consumption compare to already existing James 
>>parts like POP3 and UserRepositories?
> The normal SMTP/POP life-cycle is 1. delivering a message 2. retrieve by
> pop3, store on users hard-disk, delete from server. The user will sort
> and archive his messages on his own computer. 
> With IMAP all messages stay on the server. The client is not required to
> cache anything. The user will browse through the mailboxes fetch headers
> and content, perform searches, copy messages.
> With POP3 mailboxes with the size of a GB are very unlikely. 
> IMAP is designed to keep a TCP connection open all the time do be
> informed when new mail arrives. Clients are even opening multiple
> concurrent connections when browsing through mailboxes.
> In a worst case, when nobody is ill or on holidays, you have at least
> one open connection per user all the time. 

OK, thank you for explaining (although I am not completely with you on 
the POP3 mailbox size case, since I am keeping all my POP3 mails on the 
server, too ;-) ).

>>I would have guessed think that the resource consumption is not 
>>depending on the protocol in the first place, but on the number of 
>>users, the number of transmitted emails and the size of those emails.
> Yes, but on IMAP the user is dealing with the same message several
> times.
> Of course it's not the protocol itself but the way it is used.
>>This requires to share the load
>>>between multiple hosts. Another goal is being fault tolerant and to have
>>>a fail-over strategy. This means not having 99.999% availability. This
>>>could be done using a cluster capable RDBMS. At the best this would mean
>>>that you can setup your IMAP servers like accessing one single database.
>>Are you still talking about James at this point or some specialized IMAP 
>>server apart from James?
> For accessing a DB cluster you don't need any specialization. Any
> application that uses JDBC should be able to do it quite out of the box.

Keeping the whole of James in mind, I think it is more worthwhile to 
think about clustering James instead of clustering IMAP servers using 


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