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
RDBMSs.
Bernd
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