On Tue, Jun 23, 1998 at 11:50:58AM -0300, Alexandre dos Santos wrote:
/var/mail stays at a Solaris 2.5 machine. Cucipop is working at the
same machine. It's fine there. But, I want to have more than one machine
with cucipop and when I put cucipop at another machines, NFS clients, it
is delaying more 30 or 40 seconds to close the session.
NFS mounting /var/mail is a good way to get bad performance,
especially when you're doing any NFS writes. Even if you're not
doing any NFS writes, just having to deal with local file
locking and trying to translate that into NFS file locking is a
nightmare (in general, file locking is one of the single biggest
problems left with NFS).
Procmail is working good on NFS, it finishes quickly. But when
cucipop is put on a NFS client, procmails starts to delay too.
Procmail probably isn't writing to NFS, or if it is, it's
probably not using the same locking mechanism as cucipop.
Unfortunately, each vendor and each program have their own ideas
on how to best do that.
Also, keep in mind that any POP3 server will have to copy
the mailbox in order to work on it, and many of them copy the
mailbox to /var/mail/.username (you got it -- creating lots of
NFS writes).
When they're done, they copy the mailbox back to
/var/mail/username (after they copy any new mail messages that
have come in to the end of /var/mail/.username and locked then
truncated the original /var/mail/username file).
This is a *real* nightmare when you start talking about
users who select "Leave mail on server" and have multi-megabyte
mailboxes.
I think maybe now you're starting to understand why POP3
really doesn't scale well at all in multi-machine environments
(unless you've cooked up a custom mail store that uses a real
database back-end, like Oracle Parallel Server), with /bin/mail
(or procmail) as a writable interface to this message store and
POP3 and/or IMAP as a readable (and writable) interface to this
same message store. Then you can let the database vendors deal
with the hard data replication and distribution problems.
Otherwise, it's a pain-in-the-ass.
Is there another good pop server?
Have you tried QPopper from Qualcomm? It's the single best
POP3 server I've ever run across, although I wouldn't put even it
in an NFS write environment.
BTW, I used to be the Mail Systems Administrator for GNN
(Global Network Navigator), the web site/National ISP
co-operative between O'Reilly & Assoc. and AOL. At our peak, we
had hundreds of thousands of registered users, of which up to
five to six thousand were logged in at any one time, with their
MUA set to check their mail every minute.
We had a single primary Mail/POP3 server machine (Dec Alpha
2100 w/ four 250Mhz processors, 4GB RAM, 28GB hardware
mirrored/striped mail spool), and one warm spare (same CPU/RAM
configuration, physically hooked up to the same disks, but
through DECsafe ASE not mounting them unless the primary died).
--
Brad Knowles _ _
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