Re: [Exim] Delivery optimization tips for large lists ?

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Author: Peter Radcliffe
Date:  
To: exim-users
Subject: Re: [Exim] Delivery optimization tips for large lists ?
Pete Naylor <pete@???> probably said:
> Nobody can help you if you misuse the software. You should configure it
> appropriately for your needs.


I expect things to be set up reasonably by default. The default time
for caching negative hits was way too long.
I don't see any misuse in expecting reasonable defaults.

> That would be a nice feature to add, but it's not terribly important.


*splutter*

> Please explain in more detail. I fail to see how round robin DNS is
> related to providing multiple mail servers with any sort of failover
> mechanism so I have to assume that this is another case of misuse.


The MX record for example.com points at mail.example.com.
mail.example.com has two A records, 10.0.0.1 and 10.0.0.2, two
distinct machines for failover. nscd caches mail.example.com as
10.0.0.1 when someone sends mail to example.com. 10.0.0.1 goes down.
Mail never reaches 10.0.0.2 until the first A record times out from
nscd, which is a long time since nscd's default timeouts for positive
caching are quite high.

This is broken.

(Yes, I know that for this case a better solution is multiple MX
records, this is just an example relavent to the list since some
people do do it this way and nscd breaks it. Any system that uses
failover with multiple A records is broken in this way with nscd)

> > If you need it for passwd or other caching, fine (you can set it to
> > just cache the things you want it to cache), but using it to cache DNS
> > is broken. This is what caching name servers are for.


> They're very different applications though, and each has its pros and
> cons. An ideal solution probably involves using both (though I wouldn't
> necessarily run named on the same host).


If you are only using DNS for name service they are the same
application - making and caching DNS lookups. Just that nscd doesn't do
it correctly.

If it works for you, great. It caused me horrible problems and until
those problems are fixed I'm not going to use it, but please don't be
so uncouth as to insult me by claiming I'm abusing something so it
doesn't work.

P.

-- 
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