Re: maxring vs. maxchannel

[mea@nic.funet.fi]

> Matti,
> 
> please could you say a few words about maxring?  In the docs, it is not
> clear under what circumstances threads are grouped into one ring; and
> I noticed that here Zmailer never starts more than maxring smtp agents.
> Maybe writing some words on this topic in the doc would be a good idea...
> 
> Eugene

The basic form of selector is  channel/host -- add some wild-carding.
If you have ONLY ONE possible selector matching your destination addresses,
for given CHANNEL, then lower of maxchannel/maxring will give the limit
on number of transport agents possible on that selector.

On the other hand if you have:

*/*	# the default setting case
	maxta=150
smtp/*online.ru	# SH-GLOB  wild-card rules!
	maxchannel=100
	maxring=30
smtp/*.ru
	maxchannel=100
	maxring=20
smtp/*
	maxchannel=100
	maxring=80
local/*
	maxchannel=30
etrn/*
	maxchannel=60


Now with this set the sum of maxring cases for "smtp/" is 130,
which is more than maxchannel, so in case you have so many
threads that all of the maxring limits would peak, you will
be limited by  "channel-level" acting "maxchannel".

Now get even more active stuffs, and you local/* and etrn/*
selectors are busy too.

Sum of all maxchannel values is 190, which exceeds maxta value 150.
Thus the "maxta" will limit your startable transport agents.

There is no easy and obvious way to create a fairness mechanism so
that when maxchannel chops down on maxring, the resource rarity would
become evenly divided. (Would it even be desirable at all?)
Similar choke-point is, when maxta limits things on global scale.

On the other hand, it is possible to give selector specific exceptions
(higher/lower) on machannel/maxta limits (new values, that is), and thus
be able to favour/neglect that selector to a degree in case of system
resource limitation.


(hmm.. and now to add this into the manual..)

/Matti Aarnio <mea@nic.funet.fi>