On 2013-06-05 12:28, Vernon Schryver wrote:
I thought Google Public DNS re-fetched RRsets as they were expiring in
>order to keep the cache populated, which would explain what you see,
I don't understand how they could pre-fetch the gazillions of RRsets
that are rarely requested.
As far as I recall from some documents they published when they first
came out, they do so for some percentage of the top domains by number of
queries, not necessarily every domain that exists.
If you figure that keeping 10% of the data that passes through their
caches each day current probably covers 80%-90% of DNS queries, and they
only pre-fetch when the current TTL is getting close to expiry, it
probably does get their average latency between query and response time
down.
I'm not convinced they really bother with any of that though, I wonder
if they don't just have giant shared caches on powerful, well connected
boxes.
Either way, when you're playing with a single test domain,
experimentally, they'll absolutely expire just the way anybody else does.
--
Dave Warren
http://www.hireahit.com/
http://ca.linkedin.com/in/davejwarren
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