Re: [exim] default value seems a big low

On Thu, Aug 17, 2006 at 10:34:59AM +0100, Philip Hazel wrote:
> On Thu, 17 Aug 2006, Peter D. Gray wrote:
>
> > After 10 messages are injected via SMTP on the same
> > connection, further messages are placed in the queue
> > rather than being handled immediately.
>
> <snip>
>
> > Can someone explain the rationale behind such a low value?
>
> The rationale for having a limit is that otherwise Exim starts a
> delivery process for each message as soon as it arrives, and if 1000
> arrive quickly you would suddenly have 1000 delivery processes all
> trying to run at once.
>

Yes, the limit is a good idea.

> > It would seem to me that treating messages delivered in the
> > same connection differently to those arriving
> > on different connections is not actually that helpful
> > but maybe I just have not thought this through enough.
>
> You can limit the number of different connections. If you have set that
> to, say, 100, and messages come in very fast over those 100, you might
> have (with the default setting) 1000 deliveries going on simultaneously,
> but no more. Without the limit on each individual connection the number
> could get a lot higher. Agreed, it's unlikely that all 100 connections
> will be spewing messages in this fast, but some limit is needed IMHO.
>
> As to the value of 10, well, yes, it's small. Partly that was me being
> conservative, and partly it's because it was invented some time ago
> (1998) when machines were less powerful, and partly it's because most
> connections only send one message anyway...
>

I think you should at least consider making the limit 0 by default.

It seems to me that most (in fact nearly all)
of the "rate limiting" settings
in exim are turned off (eg queue_only_load). The assumption
seems to be that if you want/need rate limiting, you turn it
on yourself. The default value for smtp_accept_queue_per_connection
seems a notable exception and may catch people out. It certainly
caught me. As MTA's get smarter, they tend to batch things
more and more.

Just my 2c worth.

And thank you for the prompt reply.

Regards,
pdg

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