Is asychronous DNS lookup worth keeping at all?

[Eric S. Raymond]

Chris Johns <chrisj at ntpsec.org>:
> I think we need to have asynchronous support for any operation that runs in
> a synchronous manner to the main loop processing and could.
> 
> The basis of this assertion is the effect these types of operations have on
> the main processing loop. My concern is jitter effects on the time and flow
> on effects based on slow DNS or failing DNS responses causing a back log of
> events or network data. This is now in an area I am not familiar with in
> NTP, ie it's protocols and time management, and I am happy with being told
> otherwise.
> 
> In relation to DNS it is configuration changes, errors and delays which seem
> to be the issue. We have DHCP lease changes or other interface related
> changes to manage. There is a 1 second (or so) poll of the DNS configuration
> and a DNS back off which is present in the DNS asynchronous processing. They
> must be present for a reason.

Interesting point.  I had not considered the effect of DNS lookups
during operation on jitter.  I thought going synchronous would merely
delay startup om most cases, and introduce some muild lag in the pool case
- but maybe I don't know enough about the pool case

> Finally looking at this from the other direction, how do we make a case that
> removing the support will not effect all users from big to small, from
> complex to simple? Would it be more painful to incrementally add it back in
> based on freedback from important users?

Probably significantly more painful.

OK, mend it rather than ending.
-- 
		<a href="http://www.catb.org/~esr/">Eric S. Raymond</a>