Re: Finding the Bottleneck
By the way,
In addition to checking the disk usage, memory, and the other
suggestions that have come up on the list, have you looked at DNS? Quite
often you'll find that DNS lookups are severely limiting the performance
of something like a mailing list. Make sure that the mail server itself
isn't running a DNS server. Make sure you've got one or two DNS servers
in close proximity to the mail server. Make sure that the DNS server
process isn't swapping on the DNS servers (for the kind of traffic
you're pushing through, you may need a pentium class machine with 128 MB
of RAM as your DNS server. Also, if possible, I like to have the DNS
server I'm querying kept free from being the authoratative server for
any domains (not always practical in a real life situation, I know).
Also, there are probably some optimizations you can do for queue sort
order. I'm most familiar with Sendmail, not qmail, so I don't know the
exact settings, but try to process the queue according to recipient
domain. That way, you gain some advantages with holding SMTP connections
open to a server, rather than closing and reopening a session, etc.
Jason Lim wrote:
> Hi all,
> I was wondering if there is a way to find out what/where the bottleneck of
> a large mail server is.
> A client is running a huge mail server that we set up for them (running
> qmail), but performance seems to be limited somewhere. Qmail has already
> been optimized as far as it can go (big-todo patch, large concurrency
> patch, etc.).
> We're thinking one of the Hard Disks may be the main bottleneck (the mail
> queue is already on a seperate disk on a seperate IDE channel from other
> disks). Is there any way to find out how "utilized" the IDE channel/hard
> disk is, or how hard it is going? Seems that right now the only way we
> really know is by looking at the light on the server case (how technical
> ;-) ). Must be a better way...
> The bottleneck wouldn't be bandwidth... it is definately with the server.
> Perhaps the CPU or kernel is the bottleneck (load average: 4.84, 3.94,
> 3.88, going up to 5 or 6 during heavy mailing)? Is that normal for a large
> mail server? We haven't run such a large mail server before (anywhere
> between 500k to 1M per day so far, increasing each day), so ANY tips and
> pointers would be greatly appreciated. We've already been playing around
> with hdparm to see if we can tweak the disks, but doesn't seem to help
> much. Maybe some cache settings we can fiddle with? Maybe the mail queue
> disk could use a different file cache setting (each email being from 1K to
> 10K on average)?
> Thanks in advance!
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