Dave Warren <da...@hireahit.com> wrote: > On 2016-03-24 09:46, Ray Bellis wrote: > > On 24/03/2016 16:41, Tony Finch wrote: > > > > > >When I changed our TTLs from 24h to 1h last year, it didn't have a > > > >visible > > > >effect on authoritative server query load, much to my surprise. > > > > I'm not that surprised - there's definitely not a linear correlation > > between the TTL of an RRset and how frequently it's queried. > > > > Unless your TTL is very short, forced expulsion from cache (due to > > cache-size limits) would cause many clients to re-query for a record far > > more frequently than once-per-TTL. > > Has anyone ever done any evaluation on this? For average resolvers, what > is the longest TTL that has any utility?
There was a great paper published 15 years ago describing a study of DNS cache effectiveness at MIT. http://nms.csail.mit.edu/projects/dns/ It concluded (amongst other things) that NS records (and associated address records) are really important, but leaf records that users ask for don't matter so much. (Based on cache hits before TTL expiry, IIRC.) I don't know of a similar study performed more recently. https://00f.net/2012/05/10/distribution-of-dns-ttls/ is also interesting. Tony. -- f.anthony.n.finch <d...@dotat.at> http://dotat.at/ - I xn--zr8h punycode Southeast Iceland: Westerly, becoming cyclonic later, 6 to gale 8, increasing severe gale 9 for a time. Moderate or rough, becoming rough or very rough. Occasional rain, wintry showers for a time. Moderate or good, occasionally poor. _______________________________________________ Please visit https://lists.isc.org/mailman/listinfo/bind-users to unsubscribe from this list bind-users mailing list bind-users@lists.isc.org https://lists.isc.org/mailman/listinfo/bind-users
