On 21/05/2010, at 1:42 AM, Joe Abley wrote:
On 2010-05-20, at 09:22, Nathan Ward wrote:
Who on produced this report? Can they come to the next NZNOG meeting for a flogging?
There are grains of truth in the idea that increased latency between clients and resolvers can lead to decreased performance for web applications. Many of the newfangled javascript-riddled sites that the kids seem to like these days use deliberately-randomised URIs and similar techniques deliberately to defeat caching, since caching for some interactive web $buzzword.$excitement apps leads to user pain and suffering.
Vixie presented some data at the recent DNS-OARC meeting in Prague which described a trend for decreasing DNS cache hits, and at least in some cases found that random-looking URIs were contributing to the effect (see https://www.dns-oarc.net/files/workshop-201005/vixie-oarc-Prague.pdf).
If an application like Facebook can generate a few hundred HTTP sessions per page load, it seems possible that cache misses (both in DNS and HTTP caches, remote and local) give a greater effect that you would imagine, and perhaps the cumulative effect of Dunedin-Auckland DNS latency has some noticeable effect. But I agree it seems like a stretch (every cache miss in Auckland probably requires a trip to an authority-only server across an ocean).
It's quite common to use random hostnames to encourage web browsers to parallelize sessions, as (from memory) most browsers will not open more than 4 connections to a single hostname/port.
Some actual science might be nice to see, maybe.
Yep. -- Nathan Ward