[dns-operations] More Aggressive prefetch for popular names

[Paul Hoffman]

On 10 Apr 2019, at 23:56, Giovane Moura wrote:

>> However, if
>> the name was served from the cache during the last 25% of the TTL,
>> that's a good indication that it will be requested again after the
>> TTL has expired.
> I think we could really use some large-scale measurement studies on
> caches to understand their actual behavior. Things in the wild tend to
> behave sometimes quite differently from what we expect.

Yes, that is becoming obvious to even the most hesitant among us.

> While I agree with the general idea, it would be nice to see if that's
> what happens in the wild.
>
> Any resolver ops in here that have some data on this?

Yes, please. This might be tricky to do and require many cache dumps in 
quick succession, but it would be really valuable to the community.

>> Using this non-aggressive pre-fetching "requested
>> from the cache during the end of lifetime" rule seems useful to
>> resolver users while only increasing the authoritative load in the
>> less common cases.
> "only increasing the authoritative load in the less common cases."
> That's where it can get tricky. In theory, yes, but in practice it's
> hard to estimate the aggregate effects from such policy -- it may as
> well lead to some unintended collateral damage -- and IMO we need more
> studies on this.

Fully agree. This could even be aided by some resolver developers adding 
a debug feature.

--Paul Hoffman