In my current setup I use XName.org and Afraid.org for free Secondary DNS. These servers try to do an IXFR before requesting an AXFR. According to RFC1995 IXFR can either send only the changed records of a zone or the entire zone (just like an AXFR).
The attached patch implements that (based on SVN 998)
Attachment '' (ixfr-fix.diff) https://gist.github.com/5466610
Fixed in commit 1103
make pdns-distributes-queries use a hash so queries get sent to the s…
…ame thread. Original ideal from paddg@9e17697
Astoundingly effective, approximately halves CPU usage.