[dns-operations] prefetching and thundering herds

Tony Finch dot at dotat.at
Wed Jul 15 11:42:05 UTC 2020


I've been wondering about the effects of stub resolvers with caches as
clients of recursive servers. To what extent do they cause a thundering
herd effect where all the cache entries expire with the same deadline?
The herd will arrive when the RRset expires so most of those clients will
hit maximum latency and stress the server's query deduplication mechanism.

(I don't think I have enough traffic to get a useful answer from my
servers right now.)

If thundering herds happen, do they thunder enough to help explain the
lack of benefit from prefetching observed by PowerDNS?

Or maybe is the herd is too small to thunder? Instead there's a more
gentle swell of queries after the TTL expires?

https://lists.dns-oarc.net/pipermail/dns-operations/2019-April/018605.html

If there is much of a herd, would it make sense to give some proportion of
the clients a slightly reduced TTL so that they will trigger prefetch
before the rest of them requery?

Tony.
-- 
f.anthony.n.finch  <dot at dotat.at>  http://dotat.at/
Bailey: Southwest 4 or 5, increasing 6 or 7 later. Moderate or rough,
occasionally very rough later in far northwest. Drizzle, fog patches. Moderate
or poor, occasionally very poor.


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