Models of DNS traffic and caches

Are there any analytic or simulation models of DNS traffic and caches? Say I have a DNS cache that handles two different kinds of traffic, DNSBL lookups that are almost never reused, and web page lookups that are frequently reused. Is there a model that will predict whether partitioning the cache would be a good idea, or capping TTL on the DNSBLs, or other sorts of tricks? Pointers are fine. TIA. R's, John -- Regards, John Levine, johnl@iecc.com, Primary Perpetrator of "The Internet for Dummies", Please consider the environment before reading this e-mail. http://jl.ly