It takes 2,5 minutes to rebuild one domain use djbdns on my system ! It's just super crazy slow...
And my system is on Virtualbox machine 2x Intel Xeon X5570 2.93 GHz, 32 GB DDR3 1066 MHz (from 48 GB in host machine), 3x SSD HARDWARE RAID0 + 4GB cache !
Kloxo should should create just master text files first then just build whole database at the end when running /script/fixdns !