[Dnsmasq-discuss] Any plans on adding ability to store cachetodisk?
Timothy Madden
terminatorul at gmail.com
Tue May 15 18:46:35 BST 2012
Nicholas Weaver wrote:
>>> gypsy wrote:
>>>
>>>> If Simon is offended, then so be it, but I mean no offense. I just fail
>>>> to see how a save to/restore from disk could bloat the code;
>>>> save/restore IS a basic feature. TTL will expire out any crap
>>>> naturally.
>>>> --
>>>> gypsy
>
> Speaking as just a general DNS guy (I'm not a DNSMasq developer): Saving
> cache state is stupid.
>
> TTL dictates a MAXIMUM that data can remain in the cache, but doesn't
> dictate a minimum, as any "minimum" could be enforced on the authority
> side by simply ensuring that the answer is consistent.
>
> The savings is also trivial: It only saves one RTT to the recursive
> resolver per lookup, since the recursive resolver should still have the
> item in its cache. And this should be a short RTT: if your ISP doesn't
> have the recursive resolver within 30-40ms of your system, its either a
> high latency link overall (in which case amdahl's law ensures that the RTT
> for DNS lookups are still going to be irrelevant).
Exactly why should the recursive resolver have the site in its cache for the
entire TTL of the site name ?
And if it happens not to have it, a new lookup costs about 2 seconds in my
case.
Timothy Madden
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