In article <mailman.454.1458858570.73610.bind-us...@lists.isc.org>, Dave Warren <da...@hireahit.com> wrote:
> On 2016-03-24 15:20, Tony Finch wrote: > > 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. > > The internet was a very different place 15 years ago, in particular, > this was before every Windows client machine had it's own DNS cache > service and largely before today's connected mobile devices were a thing. But it was also before the widespread use of CDNs (Akamai was founded only 3 years earlier). These days, the most heavily used web sites use CDNs, which make heavy use of short TTLs for the leaf CNAME and A records. -- Barry Margolin Arlington, MA _______________________________________________ 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
