Measuring spare capacity

Wed Dec 8 09:32:33 GMT 2004

Hi Martin,

Thank you for your quick response.

Two dual Xeon HT machines with 2GB RAM running Fedora Core and sendmail.
We have tuned the systems for performance already.

It's not so much that we want to get more performance out of the system,
(although that would be nice). We rather want to be able to do some
capacity planning.

When we have a problem with the service all we see is a spike in the
number of messages in mqueue.in. It seems that the systems have a 'trip
point'. Before this point they are able to keep the queue down to one or
two, after it the queue rockets to thousands of messages.

I'm after a metric I can get from the systems which tells me how far I
am away from this 'trip point'. Something like: 'the current load is
5000 messages per hour. The system will trip at 7500 messages per hour'.
The load, CPU and memory graphs in MRTG are flat, apparently random or
spiking with the queue. I don't have any figures that show that the
system has less spare capacity during the day compared to the middle of
the night, which is what I expect to see.

If we can work out the spare capacity, then we can plan for additional
system(s) to ensure that we do not run into trouble.

Bart...

-----Original Message-----
From: MailScanner mailing list [mailto:MAILSCANNER at JISCMAIL.AC.UK] On
Behalf Of Martin Hepworth
Posted At: 07 December 2004 15:44
Posted To: MailScanner
Conversation: Measuring spare capacity
Subject: Re: Measuring spare capacity

Hi

what hardware and what OS/MTA???

what performance tuning have you done

what does load average look like?

might want to reduce batch set and max children to see how it gets
on..theses params are very much trial and error...

--
Martin Hepworth
Snr Systems Administrator
Solid State Logic
Tel: +44 (0)1865 842300

MailScanner wrote:
> I am trying to get a handle on the amount of spare capacity in my MS
> boxes.
>
> We are running two MS which handle about 250,000 messages by day (MRTG
> count by recipient). The 'Max Unscanned Messages Per Scan' and Max
> Unsafe Messages Per Scan' are both set at 50 and max children at 15.
>
> I isolated a day's worth of maillog entries out of a rotated file and
> looked at some stats. Counting all instances of 'Found X messages
> waiting' I found that 75% had just one message, 17% two, 5% three and
> the more populous batches hardly registering at all. Doing the same
for
> 'Scanning X messages' I found a slightly wider spread but tapering off
> quickly after 15.
>
> These are the distributions for the first 15 counts:
>
> New Batch: Scanning $a messages,
> 1       36153
> 2       8187
> 3       2188
> 4       767
> 5       319
> 6       139
> 7       70
> 8       45
> 9       18
> 10      11
> 11      17
> 12      6
> 13      4
> 14      3
> 15      5
>
> Found $a messages waiting
> 1       0
> 2       7545
> 3       7019
> 4       5126
> 5       3484
> 6       2535
> 7       1724
> 8       1238
> 9       915
> 10      618
> 11      489
> 12      372
> 13      260
> 14      211
> 15      161
>
> This surprised me. I was expecting the batch size to grow during busy
> periods. It seems that the batch size is generally a single message,
> even though more messages are waiting to be processed. Looking at log
> snippets in the mailing list archives confirms that this is common.
> Looking at the time distribution of (rather rare) larger batches I
found
> these spread randomly over the day.
>
> We regularly get a peak in the incoming messages queue of a few
> thousands of messages. This makes me believe that there is not that
much
> slack in the capacity. During these peaks the number of messages per
> batch does go up to the maximum.
>
> Is there a way to measure how many more messages per day a given
system
> can take?
>
> Thanks for any ideas.
>
> Bart...
>
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