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On Sat, 12 Feb 2000, Matti Aarnio wrote:

> Hi,
> 	Some colleques of mine asked for a method to construct
> 	a load-balance cluster of ZMailer servers, and below you
> 	can see some initial thoughts on that regard.
> 	So far I have a model of doing it, implementation hasn't
> 	yet begin properly -- Scheduler MAILQv2 is sort of pre-
> 	requisite for this, for example..
> 	Any thoughts, comments, text fixes, code ??

Some thoughts yes..

At UUNET NL I implemented a new Zmailer farm for doing smtp, fallback,
uucp and etrn. All on separate machines with fallbacks.

For ETRN this was the most difficult. We don't let our ETRN machines poll
the clients, but when a customer dials in the radius servers send a ETRN
request for them and the mailrun is started up.

When you have multiple servers with function ETRN and a lot of customers
working with the product it's not efficient to trigger a mailrun every
time a clients dials in. Most of the time there's no mail for them.
At the moment we also trigger mailruns when a customer dials in (mostly
by ISDN) and adds a second line for more speed at some time.

What I did to solve the problem of unneeded mailruns was to pull the
knowledge of which client has mail in the queue from the etrn machines to
the radiusservers.
So at this moment, when a client dials in, the radius server knows (with a
small delay) if and where mail is being held for that client, and only if
there's mail a mailrun is triggered.
This resulting in dropping the number of mailruns by 70%

What would be very nice to see thus in a ETRN cluster is a way to poll 
on which servers there's mail for someone. Of course when you have all
servers try at some random time by thereselves there's no need for such a
thing. But in busy environments this can really make a difference.

More thoughts begin to develop in my head, but I need to check my notes 
at the office for more...to be continued


Mark Visser / Calslaan 26-31              | E-mail: mark@dnd.utwente.nl
7522 MC Enschede / Telephone: 053-4895038 | SNT-mail: mark@snt.utwente.nl
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