[inkyoto]

This could be a great fit for Prolog, in fact, as it excels at the search.

Each resolved record would be asserted as a fact, and a tiny search implementation would run after all assertions have been made to resolve the IP address irrespective of the order in which the RRsets have arrived.

A micro Prolog implementation could be rolled into glibc's resolver (or a DNS resolver in general) to solve the problem once and for all.