Autor: Vadim Vygonets Data: A: exim-users Assumpte: Re: [Exim] Caching DNS and Exim
Quoth Nigel Metheringham on Mon, Mar 27, 2000: > Unhelpfully... it depends!
> If you have a nearby (ie direct ethernet connected DNS server with
> sufficient resources) DNS server then its unlikely to make much
> difference
And if you don't have a nearby DNS server, you should.
> and could possibly be slower to use a same machine server
> due to context switches.
I don't think it would be slower. I have not measured it, but I
assume that sending a DNS request on a network (even gigabit
ethernet -- the bottleneck is not the wire) and getting a
response back will take more time than context switching between
two processes. And sending a DNS request requires a couple of
context switches, too.
Of course, it may depend on your hardware and kernel...
> DNS servers need memory.
A local DNS cache which serves one mailserver will not eat much
memory, I think. However, it depends on various parameters, such
as the amount of mail traffic, whether RBL is used, etc.
(by DNS cache I mean a caching-only BIND.)
> If a local server would be pushed into swap
> then thats seriously bad.
Very true.
> In theory a local ncsd or similar cache could be good. In practice
> they are evil and should be destroyed immediately :-)
