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Re: Finding the Bottleneck

I have also thought about that... but if you have a look at Qmail's
website (http://www.qmail.org) then you'll see that a number of extremely
large mail companies (hotmail for one) uses qmail for... get this...
outgoing mail. They could've easily chosen sendmail, postfix (maybe it
wasn't around when they designed their systems), zmailer, etc. but those
chose qmail.

Why would that be?

I'm not sure about exim (haven't used it before) but qmail can open (after
patching) over 500 or even 1000 concurrent outgoing connections. I've
patched and recompiled qmail to send 500 concurrent outgoing emails, which
I thought would be plenty. Unfortunately, I haven't had the opportunity to
ever see it go that high because (as Russell is suggesting) the hard disks
just cannot feed mail fast enough into the system. Most I've ever seen it
go was approximately 250 concurrent emails. And who said bandwidth is
always the limiting factor?

If only there was some simple way to spread the mail queue over 2 disks
naturally (not by raid).
In the /var/qmail/queue directory,
sh-2.05# ls -al
total 44
drwxr-xr-x   11 qmailq   qmail        4096 Jun  8 09:04 .
drwxr-xr-x   13 root     root         4096 Jun  8 15:24 ..
drwx------    2 qmails   qmail        4096 Jun  8 21:54 bounce
drwx------   25 qmails   qmail        4096 Jun  8 09:04 info
drwx------   25 qmailq   qmail        4096 Jun  8 09:04 intd
drwx------   25 qmails   qmail        4096 Jun  8 09:04 local
drwxr-x---    2 qmailq   qmail        4096 Jun  8 09:04 lock
drwxr-x---   25 qmailq   qmail        4096 Jun  8 09:04 mess
drwx------    2 qmailq   qmail        4096 Jun  8 21:54 pid
drwx------   25 qmails   qmail        4096 Jun  8 09:04 remote
drwxr-x---   25 qmailq   qmail        4096 Jun  8 09:04 todo

However, as Russell also mentioned in a previous email, qmail uses inode
numbers extensively for the queue, so there would be a huge headache in
splitting them up as the system would be unable to cope with 2 different
inodes from 2 different hard disks. :-/


----- Original Message -----
From: "Peter Billson" <pete@elbnet.com>
To: "Jason Lim" <maillist@jasonlim.com>
Cc: <debian-isp@lists.debian.org>
Sent: Friday, June 08, 2001 8:04 PM
Subject: Re: Finding the Bottleneck

> > Additionally, as far as I can see, most emails get sent to the same
> > moderately large list of domains (eg. aol), so the local DNS server
> > would've cache them already anyway.
> This has been a long thread so forgive me if this has already been
> discussed but...
>   If you are usually delivering multiple messages to a handful of
> domains wouldn't the performance be greatly improved by using Exim or
> Sendmail that is capable of delivering multiple messages per connection?
> Particularly if AOL is involved since I have seen it take four or five
> attempts to get a connection to their SPAM clogged mail servers.
>   If I understand q-mail correctly it does one message per connection
> and opening/closing the connection often takes longer then transmitting
> the data.
> DISCLAIMER: This post is not intended to start a religious war over
> which mail transport program is best! :-)
> Pete
> --
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