For what is is worth, and if anyone is interested, here are some stats from the processing after I introduced the *nix sort before my perl script.

 elapsed time    | type      |rows after| rows before| pct   | rows/second 
                 |           |processing| processing |smaller| 
 00:03:05.98667  | dns       |  1791555 |    4614653 | 38.82 | 24811.7405403301
 00:03:50.106203 | dns       |  2262736 |    5822777 | 38.86 |  25304.737221708
 00:04:51.91195  | dns       |  2733705 |    7039758 | 38.83 | 24116.0322487654
 00:05:36.348691 | dns       |  3208365 |    8266995 | 38.81 | 24578.6447850335
 00:06:33.947878 | dns       |  3683419 |    9490938 | 38.81 | 24091.8622234589
 00:07:35.58667  | dns       |  4155971 |   10705249 | 38.82 | 23497.7221787459
 00:08:25.086565 | dns       |  4633553 |   11946401 | 38.79 | 23652.1852447214
 00:09:07.952743 | dns       |  5109618 |   13183845 | 38.76 | 24060.1861536808
 00:10:16.250404 | dns       |  5596902 |   14441405 | 38.76 | 23434.3132373833
 00:10:54.578348 | dns       |  6070888 |   15662586 | 38.76 | 23927.7483709253
 00:11:39.012952 | dns       |  6547181 |   16896184 | 38.75 | 24171.4891714911
 00:12:43.13814  | dns       |  7019314 |   18113219 | 38.75 | 23735.1772249255
 00:13:34.23578  | dns       |  7499659 |   19365386 | 38.73 | 23783.5114541392
 00:14:35.939246 | dns       |  7973633 |   20591767 | 38.72 | 23508.2137191967
 00:15:12.223167 | dns       |  8448494 |   21815382 | 38.73 | 23914.5231004641
 00:15:52.951662 | dns       |  8923786 |   23043433 | 38.73 | 24181.1142357817
 00:17:45.637116 | dns       |  9402613 |   24278649 | 38.73 | 22783.2238906363
 00:17:52.402055 | dns       |  9880079 |   25516948 | 38.72 | 23794.1990888856