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Subject: Re: Scalability metrics?
From: Brad Knowles (blkskynet.be)
Date: Fri Feb 11 2000 - 16:41:54 CST

At 1:39 PM -0500 2000/2/11, Jeff Johnson wrote:

> Wait a minute? X-UIDL? If the problem is 50/50 read/write ratio, then why
> don't you just have your users use IMAP to access their mailbox?

        You get a 50/50 read/write ratio with POP, and if you have to
rewrite the message, you get a 33/66 read/write ratio, which is even
worse. Allowing users to use IMAP would simply encourage them to
leave their mail on the server even more than they do, and this is
already a big enough problem as it is.

        And that still wouldn't solve the 50/50 read/write ratio problem.
And, this doesn't solve the problem of 16MB messages coming in for
250 users meaning 4GB of data to write.

> You avoid writing X-UIDL's, you can still use Maildir (if using Cyrus, you
> are writing maildir style anyway), and you read when needed.

        Even if you can somehow manage to avoid X-UIDLs, you still get a
typical 50/50 read/write ratio, which is known to be the worst
real-world case for NFS server performance. NFS works really well
when you get very small percentages of writes, and everyone else
mounts the filesystem read-only.

> We have about 40,000 mailboxes on a single machine, some with as many as
> 30,000 messages in each mailbox, and we haven't had problems yet. Then
> again, most mailboxes are realitively small.

        And we've got two different machines with 240,000 mailboxes each,
one of which is a more powerful server using the older
mailbox-per-user paradigm and only handles part of the service (which
we believe we can now scale to at least 360,000 mailboxes or more),
while the other one is a less powerful server handling *everything*,
but using the new paradigm which eliminates mailbox-per-user. 

-- 
   These are my opinions and should not be taken as official Skynet policy
  _________________________________________________________________________
|o| Brad Knowles, <blkskynet.be>                 Belgacom Skynet NV/SA |o|
|o| Systems Architect, Mail/News/FTP/Proxy Admin  Rue Col. Bourg, 124   |o|
|o| Phone/Fax: +32-2-706.13.11/726.93.11          B-1140 Brussels       |o|
|o| http://www.skynet.be                          Belgium               |o|
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     Unix is like a wigwam -- no Gates, no Windows, and an Apache inside.
      Unix is very user-friendly.  It's just picky who its friends are.